Sleep and its types. Dreams. Sleep disorders. Insomnia. Narcolepsy. Hypersomnia. NREM and REM phases of human sleep
Sleep is a physiological state that is characterized primarily by the loss of active mental connections of the subject with the world around him. Sleep is vital for higher animals and humans. A third of a person’s life passes in a state of periodic sleep.
Biological significance of sleep. For a long time it was believed that sleep is a rest necessary to restore the energy of brain cells after active wakefulness. However, recently biological significance sleep is considered much more widely. First, it turns out that brain activity during sleep is often higher than during wakefulness. It has been found that the activity of neurons in a number of brain structures increases significantly during sleep. In addition, during sleep, activation of a number of autonomic functions is observed. All this made it possible to consider sleep as an active physiological process, an active state of vital activity.
Objective characteristics (signs) of sleep. Sleep is characterized primarily by a loss of active consciousness. A person who sleeps deeply does not react to many environmental influences unless they are excessive. Reflex reactions during sleep are reduced. Sleep is characterized by phase changes in IRR, which are especially pronounced during the transition from wakefulness to sleep.
During the transition from wakefulness to sleep, the following phases are observed:
Equalization,
Paradoxical,
Ultra-paradoxical,
Narcotic.
Typically, conditioned reflex reactions obey the law of strength: to a stronger conditioned stimulus, the magnitude of the conditioned reflex reaction is greater than to a weak stimulus. The developmental phases of sleep are characterized by disturbances in power relations. Equalization phase characterized by the fact that animals begin to respond with conditioned reflex responses of the same magnitude to conditioned stimuli of varying strength.
During paradoxical phase To weak conditioned stimuli, a larger conditioned reflex reaction is observed than to strong stimuli. Ultraparadoxical phase characterized by the disappearance of conditioned reactions to positive conditioned signals and the appearance of a conditioned reflex response under the influence of inhibitory conditioned stimuli. IN narcotic phase animals cease to respond with a conditioned reflex reaction to any conditioned stimuli.
Another indicator of sleep status is the loss of the ability to engage in active, goal-directed activities.
Objective characteristics of the sleep state are clearly detected on the EEG and when recording a number of vegetative indicators. During sleep, a number of changes occur in the EEG, occurring in several stages. In a state of wakefulness, low-amplitude, high-frequency EEG activity (beta rhythm) is characteristic. When you close your eyes and relax, this activity is replaced by a low-amplitude alpha rhythm. During this period, a person falls asleep, he gradually plunges into an unconscious state.
During this period, awakening occurs quite easily. After some time, alpha waves begin to form “spindles.” After 30 minutes, the “spindle” stage is replaced by the stage of high-amplitude slow theta waves. Awakening at this stage is difficult. This stage is accompanied by a number of changes in vegetative parameters: heart rate decreases, blood pressure, body temperature, etc. decrease. The theta wave stage is replaced by the stage of high-amplitude ultra-slow delta waves. As unconsciousness deepens, delta waves increase in amplitude and frequency. Delta sleep is a period of deep sleep. Heart rate, blood pressure, and body temperature reach minimum values during this phase.
The described EEG changes constitute the “slow wave” stage of sleep, it lasts 1-1.5 hours. This stage is replaced by the appearance on the EEG of low-amplitude, high-frequency activity characteristic of the state of wakefulness (beta rhythm). Since this stage appears during the deep sleep phase, it is called “paradoxical” or “rapid wave” sleep.
Thus, according to modern concepts, the entire period of one sleep cycle is divided into two states, which replace each other (such a change occurs 6-7 times during the night) and differ sharply from each other:
Slow wave or slow wave (orthodox) sleep;
REM or paradoxical sleep.
The slow-wave sleep stage is accompanied by high-amplitude slow delta waves in the EEG, and the REM sleep stage is accompanied by high-frequency low-amplitude activity (desynchronization), which is characteristic of the EEG of the brain of a waking animal, i.e., according to EEG indicators, the brain is awake and the body is asleep. This gave rise to calling this stage of sleep paradoxical sleep.
If you wake up a person in the phase of paradoxical sleep, he reports dreams and conveys their content. A person waking up in the slow-wave sleep phase most often does not remember dreams.
The paradoxical phase of sleep turned out to be important for normal life. If a person is selectively deprived of only the paradoxical phase of sleep during sleep, for example, by waking him up as soon as he enters this phase, then this leads to significant disturbances in mental activity. This indicates that sleep, and especially its paradoxical phase, is a necessary state of preparation for normal, active wakefulness.
Theories of sleep.
Humoral theory: The cause of sleep is considered to be special substances that appear in the blood during wakefulness. The proof of this theory is an experiment in which a awake dog was transfused with the blood of an animal that had been deprived of sleep for 24 hours. The recipient animal immediately fell asleep. Currently, it has been possible to identify some hypnogenic substances, for example, a peptide that induces delta sleep. However, the presence of hypnogenic substances is not a fatal sign of sleep development.
This is evidenced by observations of the behavior of two pairs of unseparated twins. In these twins, the embryonic separation of the nervous system occurred completely, and the circulatory systems had many anastomoses. These twins showed different attitudes towards sleep: one girl, for example, could sleep, while the other was awake. All this indicates that humoral factors cannot be considered as the absolute cause of sleep.
The second group of theories is neural theories of sleep. Clinical observations have shown that with various tumor or infectious lesions subcortical, especially brain stem formations, patients experience various sleep disorders - from insomnia to prolonged lethargic sleep. These and other observations indicated the presence of subcortical sleep centers.
It was experimentally shown that when the posterior structures of the subthalamus and hypothalamus were irritated, the animals immediately fell asleep, and after the irritation stopped, they woke up. These experiments indicated the presence of sleep centers in the subthalamus and hypothalamus.
In the laboratory of I.P. Pavlov it was established that when a long-term and persistently unreinforced conditioned stimulus was used or when a subtle differential conditioned signal was produced, the animals, along with the inhibition of their conditioned reflex activity, fell asleep. These experiments allowed I.P. Pavlov to consider sleep as a consequence of the processes of internal inhibition, as a deepened, diffuse inhibition that spread to both hemispheres and the nearest subcortex. This is how the cortical theory of sleep was substantiated. However, a number of facts could not be explained by either the cortical or subcortical theories of sleep.
Firstly, observations of patients who lacked almost all types of sensitivity showed that such patients fall into a state of sleep as soon as the flow of information from the operating sense organs is interrupted. For example, in one patient, of all the sense organs, only one eye was preserved, the closure of which plunged the patient into a state of sleep. The patient, with preservation of sensitivity only on the dorsum of the forearm of one hand, was constantly in a state of sleep. She woke up only when they touched areas of her skin that remained sensitive.
Secondly, it remained unclear why hemispheric animals and newborn children, whose cortex is not yet sufficiently differentiated morphologically, sleep.
Many questions of the central organization of sleep processes were explained with the discovery of the ascending activating influences of the reticular formation of the brain stem on the cerebral cortex. It has been experimentally proven that sleep occurs in all cases of elimination of the ascending activating influences of the reticular formations on the cerebral cortex.
Along with this, descending influences of the cerebral cortex on subcortical formations were established. The influence of the frontal parts of the cerebral cortex on the limbic structures of the brain and hypothalamic sleep centers is especially important. In the waking state, in the presence of ascending activating influences of the reticular formation on the cerebral cortex, neurons of the frontal cortex inhibit the activity of neurons in the sleep center of the posterior hypothalamus. In a state of sleep, when the ascending activating influences of the reticular formation on the cerebral cortex decrease, the inhibitory influences of the frontal cortex on the hypothalamic sleep centers decrease.
An important circumstance directly related to the nature of sleep was the establishment of the fact of reciprocal relationships between the limbic-hypothalamic and reticular structures of the brain. When the limbic-hypothalamic structures of the brain are excited, inhibition of the structures of the reticular formation of the brain stem is observed and, vice versa.
Consequently, states of wakefulness and sleep are characterized by specific architectonics, a peculiar “layout” of cortical-subcortical relationships.
During wakefulness, due to afferentation flows from the sense organs, the structures of the reticular formation of the brain stem are activated, which have an ascending activating effect on the cerebral cortex. In this case, the neurons of the frontal cortex exert descending inhibitory influences on the sleep centers of the posterior hypothalamus, which eliminates the blocking influence of the hypothalamic sleep centers on the reticular formation of the midbrain.
In a state of sleep, with a decrease in the flow of sensory information, the ascending activating influences of the reticular formation on the cerebral cortex are reduced. As a result, the inhibitory influences of the frontal cortex on the neurons of the sleep center of the posterior hypothalamus are eliminated. These neurons, in turn, begin to inhibit the reticular formation of the brain stem even more actively. Under conditions of blockade of all ascending activating influences of subcortical formations on the cerebral cortex, a slow-wave stage of sleep is observed.
Hypothalamic centers, due to morphofunctional connections with limbic structures of the brain, can have ascending activating influences on the cerebral cortex in the absence of influences from the reticular formation of the brain stem.
The mechanisms discussed above constitute cortical-subcortical theory of sleep, proposed by P.K. Anokhin. This theory made it possible to explain all types of sleep and its disorders. It proceeds from the leading postulate that whatever the cause of sleep, the sleep state is associated with the most important mechanism - a decrease in the ascending activating influences of the reticular formation on the cerebral cortex.
The development of sleep is explained by a decrease in the ascending activating influences of the reticular formation due to inhibition of the activity of its neurons during electrical stimulation of the posterior hypothalamus.
The sleep of cortical-free animals and newborn children is explained by the weak expression of the descending influences of the frontal cortex on the hypothalamic sleep centers, which under these conditions are in an active state and have an inhibitory effect on the neurons of the reticular formation of the brainstem. A newborn's sleep is periodically interrupted only by the excitation of the hunger center located in the lateral nuclei of the hypothalamus, which inhibits the activity of the sleep center. In this case, conditions are created for the entry of ascending activating influences of the reticular formation into the cortex. The newborn wakes up and stays awake until the activity of the hunger center decreases due to the satisfaction of food needs.
It becomes clear that in all cases of severe limitation of sensory information, which occurred in some patients, sleep arose as a result of a decrease in the ascending activating influences of the reticular formation of the brain stem on the cortex.
The cortical-subcortical theory of sleep explains many sleep disorders. Insomnia, for example, often occurs as a result of overexcitation of the cortex under the influence of smoking, stress creative work before bedtime. At the same time, the descending inhibitory influences of frontal cortex neurons on the hypothalamic sleep centers are enhanced and the mechanism of their blocking effect on the reticular formation of the brain stem is suppressed.
Shallow sleep is observed with partial blockade of the mechanisms of ascending activating influences of the reticular formation on the cerebral cortex. Prolonged, for example, lethargic sleep can be observed when the sleep centers of the posterior hypothalamus are irritated by a vascular or tumor pathological process. In this case, the excited cells of the sleep center continuously exert a blocking effect on the neurons of the reticular formation of the brain stem.
The concept of “sentinel points” as partial wakefulness during sleep is explained by the presence of certain channels of reverberation of excitations between subcortical structures and the cerebral cortex during sleep against the background of a decrease in the bulk of the ascending activating influences of the reticular formation on the cerebral cortex. The “sentinel point” or focus can be determined by signaling from internal organs, internal metabolic needs and external vital circumstances.
For example, a nursing mother may sleep very soundly and not respond to strong enough sounds, but she quickly wakes up when her newborn baby moves slightly. Sometimes “watchdog points” can have prognostic value. For example, in the case of pathological changes in a particular organ, increased impulses from it can determine the nature of dreams and be a kind of prognosis of a disease, the subjective signs of which are not yet perceived in the waking state.
The hypnotic state can be defined as partial sleep. Perhaps the hypnotic state is created due to the excitation of limbic-thalamic structures against the background of the remaining part of the ascending activating influences of the reticular formation on the cerebral cortex” that determine behavioral activity.
Selective activation of the limbic structures of the brain is observed when the brain is exposed to electrical current pulses during so-called electrosleep, and a hypnosis-like state is formed.
Sleep, as a special state of the body and, above all, the state of the brain, is characterized by specific cortical-subcortical relationships and the production of special biologically active substances, is used in the treatment of neurotic, asthenic conditions, relieving psycho-emotional stress and in a number of psychosomatic diseases (early stages of hypertension, heart disorders rhythm, ulcerative lesions of the gastrointestinal tract, skin and endocrine disorders).
Pharmacological sleep is inadequate in its mechanisms to natural sleep. Various “sleeping pills” limit the activity of different brain structures - the reticular formation of the brain stem, the hypothalamic region, and the cerebral cortex. In this case, the natural mechanisms of the formation of sleep stages, its dynamics, and awakening are disrupted. In addition, during pharmacological sleep, the processes of memory consolidation, processing and assimilation of information, etc. may be disrupted. Therefore, the use of pharmacological agents to improve sleep should have sufficient medical justification.
Modern representations about the physiological architecture of a behavioral act (functional system of behavior). Any activity of the body is adaptive and is aimed at achieving a useful adaptive result for the body. The basis of this adaptive activity is the formation of functional systems, i.e., a set of processes and mechanisms that dynamically develop to achieve a useful result for the body. Consequently, the formation of functional systems is subordinated to obtaining a certain, useful adaptive result. An insufficient result can completely reorganize the system, forming a new one with a more perfect interaction of components that ensure a useful result.
Stages (nodal mechanisms) of the formation of a functional system. The concept of functional systems postulates the idea that the environment of existence influences the organism even before the conditioned stimulus acts. Consequently, when implementing a conditioned reflex, the conditioned stimulus acts against the background of the so-called pre-launch integration, which is formed on the basis various types afferent excitations.
1. Situational afferentation - the sum of afferent excitations that arise in the specific conditions of the existence of an organism and signal the situation in which the organism resides.
2. Situational afferentation acts on the body at the moment when it has one or another level of motivational arousal (motivation), which is in a state of hidden dominance. Dominant motivation is formed on the basis of a leading need, with the participation of motivational centers of the hypothalamus. From several needs, the most relevant one is selected, on the basis of which the dominant motivation arises. At the stage of afferent synthesis, the dominant motivation activates memory.
3. Any behavioral reaction, including a conditioned reflex, occurs faster if a similar situation has already occurred in life, i.e. if there are traces of past experience - memory. The significance of memory at the stage of afferent synthesis is that it extracts information related to the satisfaction of the dominant motivation.
These three types of excitations: motivational, memory and situational afferentation create pre-launch integration, against which the fourth type of afferentation operates - triggering afferentation(trigger stimulus, conditioned signal). These four types of excitations interact and ensure the formation of the First stage, the first nodal mechanism of the functional system behavior - afferent synthesis(Fig. 34).
Fig.34. Diagram of the functional system of a behavioral act (according to P.K. Anokhin).
The main condition for the formation of afferent synthesis is the simultaneous meeting of all four types of afferentations. These types of afferentations must be processed simultaneously and jointly, which is achieved due to the convergence of all types of excitations on convergent neurons. The stage of afferent synthesis leads the body to decide what kind of result should be produced in this moment, it provides the setting of a goal to which all further implementation of the functional system will be devoted.
The second stage of the functional system is decision-making(goal setting).
This stage is characterized by the following features:
Decision making is carried out only on the basis of complete afferent synthesis.
Through decision making, one specific form of behavior is adopted that corresponds to an internal need, previous experience and the environment.
At the decision-making stage, the body is freed from excess degrees of freedom, i.e., out of hundreds of possibilities after the decision is made, only one is realized. The remaining degrees of freedom make it possible to economically carry out exactly the action that should lead to the programmed result.
The decision-making stage contributes to the formation of the integral of efferent excitations; during this period, all types of excitations acquire an effector, executive character.
The third stage of a functional system is the formation action programs. At this stage, a specific goal of action and ways of its implementation are formed. Simultaneously with the formation of the action program, a copy of it is formed, which is stored in the nervous system, in the acceptor of the results of the action.
The fourth stage in the formation of a functional system is the formation acceptor of action results. This is a very complex apparatus of brain activity, which must form subtle nervous mechanisms that allow not only to predict the signs (parameters) of the result required at the moment, but also to compare (compare) them with the parameters of the actually obtained result. Information about the latter comes to the acceptor of action results thanks to reverse afferentation. It is this apparatus that allows the body to correct behavioral errors or bring imperfect behavioral acts to perfect ones. An acceptor of the results of an action is an ideal image of the future results of an action.
It is this model that is the standard for assessing reverse afferentations. Evidence has been obtained that this nervous complex, which has a high degree of multiconvergent interaction, receives excitations not only of afferent, but also of efferent nature. We are talking about collateral branches of the pyramidal tract, which, through a chain of intermediate neurons, carry “copies” of efferent messages (commands) going to effectors. These efferent excitations converge on the same intermediate neurons of the sensorimotor area of the cortex, which receive afferent excitations that transmit information about the parameters of the actual result.
Thus, the moment of decision making and the beginning of the release of efferent excitations from the brain is accompanied by the formation of an extensive complex of excitations, consisting of afferent signs of the future result and collateral copies of efferent excitations arriving along the pyramidal tract to the working apparatus. After a certain time, this same complex of excitations is joined by excitations from the parameters of the actual result obtained. The process of assessing the actually obtained result is carried out from a comparison (comparison, juxtaposition) of the predicted parameters and the parameters of the actually obtained result.
If the results do not correspond to the forecast, then a mismatch reaction occurs in the comparison apparatus, activating an orienting-exploratory reaction, which raises the associative capabilities of the brain to a higher level, thereby helping the active selection of additional information. It is this general activation of the brain, realized in the orienting-exploratory reaction, that directs the body to search for additional information. On its basis, a more complete afferent synthesis is formed, a more adequate decision is made, which in turn leads to the formation of a more adequate program of action and to action that allows one to obtain the programmed result.
When the desired useful result is achieved, a coordination reaction is formed in the acceptor of action results. The stage of afferent synthesis receives sanctioning afferentation, signaling the satisfaction of motivation. At this point the functional system ceases to exist.
The processes of coordination and mismatch that arise when comparing the parameters of the actually obtained result with those programmed in the acceptor of action results are accompanied by general reactions - a feeling of satisfaction and dissatisfaction, i.e. positive and negative emotions.
Consequently, the main stages, key mechanisms of the functional system are:
Afferent synthesis.
Decision-making.
Formation of an action program.
Formation of an acceptor of action results.
Action and its result.
Comparison of the result parameters with their model in the action result acceptor, carried out using reverse afferentation.
The synthesis of such diverse excitations is carried out on convergent neurons. It is to them that situational and triggering afferentations and excitement from motivational centers come. On these same neurons, the synthesis of these excitations with traces of previously occurring processes (memory) is carried out. The neurons on which the mechanisms of the functional system are formed are located in all structures of the central nervous system, at all its levels. The integration of these processes determines the holistic multi-level, multi-component adaptive activity of the organism.
Why did we decide to start talking about sleep? Most health problems:
1. overweight
2. metabolic disorder
3. disruption of internal organs
4. infectious and inflammatory processes
5. problems with the musculoskeletal system
Our body decides when it rests, and the main rest occurs at night during sleep.
Good, healthy sleep has a primary impact on our health, since it is at night that the body’s tissues are restored. During the day we only give the body an impulse to move towards health and feeling better. If a person does not have healthy and sufficient sleep, this threatens serious health problems in the future. The effectiveness of our daytime wellness treatments also directly depends on the kind of sleep we have.
Every person spends a third of his life in sleep, which is accompanied by a lack of consciousness and the presence of dreams. The ancient sages spoke correctly about sleep. For example, Hippocrates wrote the following about sleep:
“Whoever has a correct understanding of the signs that appear in sleep will find that they have great power for every thing. Indeed, the soul, while it serves the waking body, is divided between several occupations and does not belong to itself, but gives a certain shares its activity with each activity of the body: hearing, seeing, touching, walking, all bodily activities; thus, the understanding does not belong to itself. When the body is at rest, the soul, moving and running through the parts of the body, governs its own dwelling and performs all bodily activities. actions. Indeed, the sleeping body does not feel, but she - the soul - is awake, cognizes, sees what is seen, hears what is heard, walks, touches, grieves, ponders. Thus, whoever knows how to judge this sensibly, we know more part of wisdom..."
Sleep is a vital need for the body, more important than food. A person can go without food for about two months, but he cannot live without sleep for more than two weeks.
Physiology of sleep
According to modern research, sleep is a diffuse inhibition of the cerebral cortex that occurs as cells spend their bioenergetic potential during wakefulness. Increased heat production resulting from daily activities leads to heating of all body tissues, and heat causes active tissue destruction.
Partially destroyed tissues, especially nerve cells, cannot fully perform their own functions, and therefore they need a period of relative rest and a decrease in temperature (which is observed in sleep) to restore structures and accumulate energy. In addition, a person’s field uniform can come out of shape during sleep. physical body and travel in the surrounding space, but at the same time it is glued to the body with the help of a “silver thread”.
Sleep is a functional state of the brain and the entire body of humans and animals. During sleep, the central nervous system operates in a certain mode, the activity of internal organs at night also differs from daytime characteristics, while the active interaction of the body with the environment is inhibited and conscious mental activity is incompletely stopped (in humans).
Features of the functioning of the body in different phases of sleep
During different phases and stages of sleep, significant changes occur in the activity of the brain and the whole organism as a whole. Studies of the activity of individual neurons during FMS (slow-wave sleep) have shown that the average frequency of impulses in most brain structures decreases, although in some of them, which actively ensure the onset and progression of sleep, it increases compared to the waking state.
During REM sleep, the activity of neurons in most parts of the brain increases, reaching the level of wakefulness or even exceeding it. The excitability of neurons also changes and in the FMS, compared to wakefulness, it decreases and decreases even more in the FBS.
Despite the general decrease in motor activity during sleep, various movements are observed - from small ones (in the form of twitching of the muscles of the face, torso and limbs that occur when falling asleep and become more frequent during the period of FBS). To more massive ones (in the form of a change in position in bed) observed in all stages of sleep and often preceding a change in stages.
Cerebral blood flow in the FMS does not change significantly compared to wakefulness, but only increases in some structures. In FBS it increases significantly, exceeding that of quiet wakefulness, and at the same time the brain temperature rises. These data, as well as the characteristics of neural activity, indicate high functional activity of the brain during sleep.
When falling asleep and the first stage of FMS, blood pressure actually decreases, heart rate decreases and breathing becomes less frequent. In deeper stages of FMS, the heart rate and breathing rate increase slightly, which may occur for compensation and is necessary to maintain an optimal level of systemic blood flow and pulmonary ventilation due to a decrease in blood pressure and a decrease in the depth of breathing.
In the FBS, the performance of the cardiovascular and respiratory systems increases sharply. At the same time, along with an increase in blood pressure, heart rate and respiration, their greater dynamism is noted, manifesting noticeable arrhythmias of the pulse and respiration.
A dream similar to the one that occurs in humans occurs only in higher vertebrates - birds, mammals. In humans and many animals, there is a daily periodicity of sleep and wakefulness - the so-called circadian rhythm.
In addition to normal sleep, a distinction is also made between narcotic sleep - caused by the administration of various sleeping pills, hypnotic sleep - caused by suggestion, and pathological sleep - associated with disruption of the functioning of certain parts of the brain.
Dreams. As a rule, in dreams a person sees the same things that he sees during the day, but in other, sometimes unusual combinations. Dreams are explained by the fact that during sleep, not the entire cortex is inhibited - some of its areas continue to remain excited and create certain sensations. Dreams last a short time, most of the sleep is dreamless.
Theory and nature of sleep
The most common theories of the origin of sleep.
1. Chemical theory of sleep - explains the development of sleep by the accumulation of specific substances in the body.
2. The theory of sleep centers - connects sleep with periodic changes in the activity of the subcortical centers of sleep and wakefulness.
3. Cortical theory of sleep, according to which sleep occurs as a result of irradiation along the cortex of an inhibitory process that can descend to subcortical formations. This theory was most fully developed by I.P. Pavlov and his students.
It is assumed that during sleep, the brain processes information received during the day, redistributes it to the appropriate memory registers and fixes a memory trace. It has been proven that the latter process occurs during brain activation during REM sleep.
There are a number of theories explaining the occurrence of sleep and its functional significance. There is no single generally accepted concept on this issue yet. In particular, the information concept of sleep suggests that its function is to process information received during the waking state, unload the brain from excess, unnecessary information, and include its biologically important part in memory mechanisms.
Close to this concept is a psychological concept that considers sleep as a state during which psychological processing of an individual’s experience occurs, the emotional sphere is stabilized and psychological protection is provided.
There is an anabolic theory of sleep, which considers sleep as a restorative process during which the energy reserves of the brain and the body as a whole are restored. This is consistent with the data obtained on the occurrence of biochemical processes during sleep (protein synthesis and a number of others). A theory has been put forward that considers sleep as one of the types of instinctive behavior of animals and humans.
The sleep of humans and animals is organized cyclically. In humans, the duration of one cycle is 1.5–2 hours (3–5 cycles are observed per night). Each cycle consists of separate stages of FMS and FBS. The first appearance of FBS occurs 1 – 1.5 hours after falling asleep, following the FMS stage. Delta sleep is typical for the first two sleep cycles, while the duration of FBS is maximum during 3–4 cycles (usually in the early morning hours). On average, in a young and middle-aged person, FMS accounts for 75–80% of the duration of total sleep. FBS occupies, respectively, 20–25% of sleep duration. These values differ significantly from similar indicators in newborn children, as well as in old and senile age.
In parallel with the characteristic EEG changes, such changes are observed.
1. Galvanic skin response changes.
2. Electrocutaneous resistance changes.
3. Sweating and skin temperature change.
4. The activity of the endocrine system changes.
5. The activity of hormone secretion changes.
Mental activity in individual stages and sleep phases also have their own specifics. The drowsiness stage is characterized by peculiar visual images. When people awaken from deeper stages of FMS, it is often possible to receive reports of thought-like mental activity, sometimes of vague visual images that do not have the brightness and emotionality that is characteristic of typical dreams arising in FMS.
Despite the fact that there is an assumption about the presence of sleep centers in the brain, this hypothesis has not been confirmed. There are a number of brain formations known, the active activity of which ensures the occurrence and progression of sleep as a physiological process.
Obviously, it is still more correct to consider the functional state of sleep comprehensively. In the process of evolution, the simple function of sleep (ensuring rest), as it is at the lower stages of development of living organisms, becomes many times more complicated, ensuring the regulation of all functions of the body, aimed at its most effective interaction with the environment in the waking state.
Throughout life, a person's sleep patterns change. For example, in old age and old age there is a reduction in the duration of night sleep, the period of falling asleep is extended, and a person wakes up more often at night.
The reason for changes in the organization of sleep in a person in old age is biological and social factors affecting his physical and mental state.
NREM and REM phases of human sleep
There are 2 phases of sleep - slow-wave sleep (FMS) and rapid eye movement sleep (REM), sometimes the REM sleep phase is called paradoxical sleep. These names are due characteristic features electroencephalography rhythms during sleep. Slow activity is observed in the FMS and faster activity in the FBS.
Physiology of non-REM sleep
With slow-wave sleep, there is a decrease in breathing rate and heart rate, muscle relaxation and slow eye movement. As slow-wave sleep deepens, the total number of movements of a sleeping person becomes minimal. At this time it is difficult to wake him up. When awakening during slow-wave sleep, a person usually does not remember dreams.
During slow-wave sleep, the field form hovers close over the human body, so the physical body is motionless and calm, but waking a person is much easier than during REM sleep.
From a physiological point of view, during the slow-wave sleep phase, the physical body is restored (that is, minor repairs of internal organs). In the slow-wave sleep phase, the brain analyzes signals coming from internal organs, and based on these signals, the processes of healing the body are launched.
FMS (phase of slow-wave sleep) is divided into 4 stages with differing bioelectrical characteristics and awakening thresholds, which are objective indicators of sleep depth.
First stage(drowsiness) is characterized by the absence of an alpha rhythm on the EEG, which is a characteristic sign of human wakefulness. During this phase, slow eye movement is observed.
Second stage(slow sleep) is characterized by the rhythm of “sleep spindles” with a frequency of 13–16 per second. At the same time, the amplitude of the background EEG rhythm increases, while its frequency decreases compared to the first stage.
For third stage The appearance of slow rhythms in the delta range on the EEG is characteristic. At the same time, “sleep spindles” continue to appear quite often.
Fourth stage(behaviourally the deepest sleep) is characterized on the EEG by a high-amplitude slow delta rhythm. The third and fourth stages of FMS constitute the so-called delta sleep.
Physiology of REM sleep
During REM sleep, on the contrary, physiological functions are activated: breathing and heart rate quicken, the sleeper’s motor activity increases, the movement of the eyeballs becomes fast - this indicates that the sleeper is dreaming. If you wake him up 10 - 15 minutes after the end of rapid eye movements, he will talk about the dream he had.
During REM sleep, a person’s field form “travels” and all its activities through the silver umbilical cord are reflected in the movements of the physical body. It is because of this that the human body is much more relaxed than during slow-wave sleep and it is much more difficult to wake him up (for the reason that the field form needs time to return back from its journey).
But, despite the relatively greater activity of physiological functions in REM sleep compared to slow sleep, the muscles of the body are more relaxed during this period, and it can be much more difficult to wake up a sleeping person. If a person is artificially deprived of REM sleep (woke up during the period of rapid eye movements), then, despite the sufficient total duration of sleep, after 5 - 7 days he will develop mental disorders.
According to most modern experts, in the REM sleep phase the brain processes information received during the day, that is, this sleep phase is necessary for the evolution and adaptation of a person to changing environmental conditions. For example, everyone knows that the periodic table chemical elements dreamed of Dmitry Mendeleev - so this extremely important event for the world of science happened during the REM sleep phase. Everyone knows the recommendation of psychologists - “sleep with a problem” - this recommendation is also given with the expectation that in the REM sleep phase, the brain, based on an analysis of the available facts, will find solutions to the problem facing a person.
FBS (phase of rapid eye movement sleep) is distinguished by low-amplitude EEG rhythms, and in the frequency range by the presence of both slow and higher-frequency rhythms (alpha and beta rhythms). Characteristic signs of this phase of sleep are the so-called sawtooth discharges with a frequency of 4–6 per second, rapid eye movements, as well as a decrease in the amplitude of the electromyogram or a complete drop in the tone of the muscles of the diaphragm of the mouth and neck muscles.
Natural factors affecting human sleep
It has been found that intense physical and mental activity in the evening increases the duration of delta sleep, and prolonged physical inactivity causes sleep disturbances up to severe insomnia. Emotions have a great influence on the regulation of sleep, which, depending on the body’s individual reaction to them, can disrupt night’s sleep or cause changes in its structure.
Significant changes in sleep are associated with a sharp change in time zones and the daily cycle of lighting. With a rapid change of time zones in the first day, the connection between the wakefulness-sleep cycle and the circadian rhythm may be disrupted. The internal structure of sleep also changes. The first stage is shortened, the number of transitions from a deeper stage to a more superficial one decreases, and the relative duration of delta sleep increases.
Subjective and objective changes in the sleep structure of residents of mid-latitudes under unusual conditions of the polar night and polar day were noted.
The state of the Earth's magnetosphere also has a certain influence on the course of sleep. During magnetic storms, certain sleep disorders may occur.
1. A person spends a third of his life sleeping.
2. The longest period of wakefulness lasted 18 days 21 hours and 40 minutes. The record was recorded at a competition for sitting in a rocking chair. The winner paid for his achievement with hallucinations, speech and vision disorders, and memory loss.
3. The birth of a child takes 400 - 750 hours of sleep from parents.
4. 12% of people only dream in black and white. Others dream in color.
5. There are several groups of dreams that everyone sees without exception: situations at school or at work, an attempt to escape persecution, a fall from a height, the death of a person, teeth falling out, flying, failing exams, accidents.
6. 8 hours is the optimal time for sleep for a middle-aged person. Children and teenagers need 10 hours of sleep daily, and older people need about 6 hours.
7. Every second adult on Earth experiences one or more symptoms of a sleep disorder, and 13% of disorders are chronic.
8. 20% of car accidents occur due to fatigue and lack of sleep of drivers.
9. People who are blind after birth can see dreams in the form of pictures.
10. People who are blind from birth do not see pictures, but their dreams are filled with sounds, smells and tactile sensations.
11. 90% of dreams are forgotten within 10 minutes after waking up.
12. Somniphobia is a disease in which a person is afraid to sleep.
13. A person does not dream when he snores.
14. 40,000,000 prescriptions for sleeping pills are issued per year in the United States.
15. Over the past 100 years, people have begun to sleep 20% less.
Having the necessary theoretical knowledge You can properly organize your night's rest. You can read about this Sleep Rules
Additional articles with useful information
Basic rules for healthy sleepSleep is an intimate and highly individual process. Many people have their own ritual of falling asleep and waking up, and there is nothing wrong with that. It is much worse when a person regularly violates the physiological laws of sleep, thereby causing great harm to his health.
Features of sleep in childrenParents need to know that the child’s body lives according to its own laws, which are not typical for adults. A child’s sleep is significantly different from an adult’s.
Dream is a physiological process in which a person (as well as mammals, fish, birds and some insects) is in a state radically different from the waking state. This condition is characterized by altered consciousness, a decrease in the level of brain activity and reactions to external stimuli. Natural sleep is significantly different from such similar states as coma, suspended animation, fainting, sleep under the influence of hypnosis and lethargic sleep. Along with sleep in the usual sense of the word (i.e. sleep at night), certain cultures allow the existence of the so-called daytime rest or siesta. Short naps during the day are part of the traditions of many peoples. According to the results of ongoing research, regular afternoon naps can significantly reduce (by almost 40%) the risk of a heart attack. In a word, sleep is the most important element of human life and, at the suggestion of researchers, since 2008, every 3rd Friday of the first month of spring is celebrated as Sleep Day.
Basic functions of sleep
Thanks to sleep, the body receives the necessary rest. During sleep, the brain processes the information accumulated during the day. The so-called slow sleep allows you to better assimilate the studied material and consolidate it in memory. REM sleep provides the ability to simulate upcoming events at the subconscious level. An important function of sleep is also the restoration of the human immune system by activating the activity of T-lymphocytes, which resist viral infections and fight colds.
Physiology of the sleep process
Healthy sleep can last from 4 to 8 hours. However, these indicators are quite subjective, since the duration of sleep depends on the person’s physical fatigue. A significant amount of work done during the day may require a longer night's rest. Normal sleep is cyclical and is required by the human body at least once a day. Sleep cycles are called circadian rhythms. Every 24 hours, circadian rhythms are redefined. Light is considered the most important factor in sleep. The concentration of photodependent proteins in the body depends on its natural cycle. Typically, the circadian cycle is related to the length of daylight hours. Just before sleep occurs, a person feels drowsy, his brain activity decreases, and there is also a change in consciousness. In addition, a person who is in a sleepy state experiences a decrease in sensory sensitivity, a decrease in heart rate, yawning, and also a decrease in the secretory function of the lacrimal and salivary glands. Another physiological feature of sleep is a process called “vegetative storm”, i.e. when various forms of arrhythmias are observed, an increase or decrease in blood pressure, increased blood supply to the brain and secretion of the adrenal glands, erection of the clitoris and penis.
Structure of the sleep process
Any sleep is divided into several stages, which are repeated with a certain pattern throughout the night (naturally, provided that the daily schedule is absolutely normal). Each stage of sleep directly depends on the activity of one or another brain structure. The first stage of sleep is slow-wave sleep (Non-REM). The duration of Non-REM sleep is 5 to 10 minutes. This is followed by the second stage, lasting approximately 20 minutes. Over the next 30-45 minutes, another 3 and 4 stages of sleep are observed. Next, the person again falls into the second stage of slow-wave sleep, at the end of which rapid REM sleep occurs (episode 1). This is approximately 5 minutes. All of the above stages are the first sleep cycle, which lasts from 90 to 100 minutes. After this, the cycle repeats again, but at the same time the stages of slow-wave sleep are reduced, and REM sleep, on the contrary, increases. Typically, the last sleep cycle ends with an episode of REM sleep, lasting in some cases about 1 hour. A full sleep includes 5 complete cycles. The sequence in which one stage of the sleep cycle follows another, as well as the duration of each cycle, is usually presented in the form of a hypnogram. The sleep cycle is regulated by certain areas of the cerebral cortex, as well as the locus coeruleus, located in its trunk.
What is slow wave sleep?
NREM sleep (also called orthodox sleep) lasts 80 to 90 minutes and occurs immediately after a person falls asleep. The formation and development of slow sleep is ensured by the anterior parts of the hypothalamus, raphe nuclei, nonspecific nuclei of the thalamus and the middle part of the pons (the so-called Moruzzi inhibitory center). At the first stage of slow-wave sleep, the alpha rhythm decreases, transforming into slow low-amplitude theta rhythms, equal in amplitude to the alpha rhythm or exceeding it. The person is in a state of drowsiness (half-asleep), and dream-like hallucinations are observed. Muscle activity decreases, heart rate and breathing decrease, metabolic processes slow down, and the eyeballs move slowly. At this stage of sleep, solutions to problems that seem unsolvable during wakefulness are intuitively formed. At the very least, the illusion of their existence may arise. The first stage of slow-wave sleep may also include hypnogogic jerks.
In the second stage of Non-REM sleep (this is usually light and shallow sleep), a further reduction in muscle activity occurs, the heart rate slows down, body temperature drops, and the eyes become motionless. The second stage is approximately up to 55% of the total sleep time. The first episode of the second stage lasts approximately 20 minutes. The electroencephalogram shows at this moment the predominant theta rhythms and the emerging sigma rhythms (the so-called “sleep spindles”), which are essentially rapid alpha rhythms. At the moment of the appearance of sigma rhythms, consciousness turns off. However, during pauses between sigma rhythms, which occur at a frequency of 2 to 5 times per minute, a person can be easily awakened.
At the third stage of slow-wave sleep, the total number of delta rhythms is no more than 50%. At the fourth stage this figure exceeds 50%. The fourth stage is slow and deep sleep. Quite often stages III and IV are combined and called delta sleep. It is extremely difficult to wake a person during delta sleep. Dreams usually appear at this stage (up to 80%). A person may begin to talk, sleepwalking is possible, nightmares may occur and enuresis may develop. At the same time, a person usually does not remember any of the above. The third stage lasts from 5 to 8% of the total sleep time, and the fourth stage takes from 10 to 15% of the entire sleep period. The first four stages of slow-wave sleep normal person last from 75 to 80% of the total duration of this physiological process. According to the researchers, Non-REM sleep provides complete restoration of the energy expended during the day. In addition, the slow-wave sleep phase allows you to record conscious memories of a declarative nature in your memory.
What is REM sleep?
Rapid eye movement sleep is also called REM sleep, paradoxical sleep, or rapid wave sleep. In addition, the generally accepted name is the REM (rapid eye movement) stage. The REM stage lasts 10 to 15 minutes and follows non-REM sleep. REM sleep was discovered in 1953. The centers responsible for REM sleep are: the superior colliculus and the reticular formation of the midbrain, the locus coeruleus, as well as the nuclei (vestibular) of the medulla oblongata. If you look at the electroencephalogram at this moment, you can see quite active fluctuations in electrical activity, the values of which are as close as possible to beta waves. During REM sleep, the electrical activity of the brain is almost identical to the waking state. However, at this stage the person is completely motionless, since his muscle tone is zero. At the same time, the eyeballs actively move under closed eyelids, moving quickly with a certain periodicity. If you wake up a person in the REM stage, there is a 90% chance that he will report an exciting and vivid dream.
As noted above, the electroencephalogram of REM sleep reflects the activation of brain activity and is more reminiscent of the EEG of the first stage of sleep. The first episode of the REM stage lasts from 5 to 10 minutes and occurs 70-90 minutes after the person falls asleep. Throughout the entire sleep period, the duration of subsequent episodes of REM sleep becomes increasingly longer. The final episode of REM sleep can last up to 1 hour. The duration of REM sleep in a healthy adult is approximately 20-25% of the total sleep time. From one cycle to the next, the REM sleep phase becomes longer and longer, and the depth of sleep, on the contrary, decreases. Disturbances of slow-wave sleep are not as severe for the psyche as interruption of the REM phase. If any part of REM sleep is interrupted, it must be replenished in one of the subsequent cycles. Experiments conducted on mice have proven the detrimental effect of the missing REM phase on these mammals. After 40 days, the mouse deprived of REM sleep died, while the rodents deprived of slow-wave sleep continued to live.
There is a hypothesis that during the REM phase, the human brain works to organize the information received during the day. Another theory is that REM sleep is especially important for newborns, providing neural stimulation that promotes the formation and development of the nervous system.
Sleep duration
The duration of normal sleep can vary from 6 to 8 hours a day. However, this does not exclude large deviations in one direction or another (4-10 hours). If sleep disturbances are observed, then its duration can be equal to several minutes or several days. When the duration of sleep is less than 5 hours, this is considered a violation of its structure, which can lead to the development of insomnia. If you deprive a person of sleep, then within a few days his consciousness will lose clarity of perception, an irresistible urge to sleep will appear, and “dips” into the so-called borderline state between sleep and wakefulness will be observed.
Dreams
Along with the corresponding physiological process, the word “sleep” also means a sequence of images that arise in the REM sleep phase and, in some cases, are remembered by a person. A dream is formed in the consciousness of a sleeping person, consisting of a variety of subjectively perceived tactile, visual, auditory and other images. Usually the person who is dreaming is not aware that he is in a dream state. As a result, the dream is perceived by him as an objective reality. An interesting type of dreams are lucid dreams, in which a person understands that he is dreaming and therefore can control the development of the plot in the dream. It is believed that dreams are inherent in the REM sleep phase, which occurs once every 90-120 minutes. This phase is characterized by rapid movement of the eyeballs, increased heart rate and breathing, stimulation of the pons, as well as short-term relaxation of skeletal muscles. According to the results of recent research, dreams may also be characteristic of the slow-wave sleep phase. At the same time, they are less emotional and do not last as long as REM dreams.
Sleep pathologies
All kinds of sleep disorders are quite common. For example, the cause of insomnia (insomnia) can be psychosis, depression, neurosis, epilepsy, encephalitis and other diseases. Apnea is a breathing disorder of a sleeping person, the causes of which can be mechanical or psychogenic in nature. Parasomnias such as sleepwalking, nightmares, epilepsy and teeth grinding are formed and develop on the basis of neurosis. Pathologies such as lethargic sleep, narcolepsy and sleep paralysis are among the most severe sleep disorders. In case of any alarming factors associated with obvious deviations in the structure of sleep, you should seek help from a specialist.
Pharmacological hypnotics
Sleep regulation using pharmacological agents should be carried out under the supervision of a physician. Along with this, it should be remembered that long-term use of sleeping pills reduces the effectiveness of the latter. Relatively recently, the group of sedatives even included drugs - morphine and opium. Barbiturates have also been used as sleeping pills for quite a long time. Melatonin is considered one of the most progressive drugs at the moment. An equally effective treatment for insomnia is taking magnesium supplements, which improve sleep and promote the production of melatonin.
Sleep Study
According to prominent researchers of the past and present, sleep plays a more important role for the human body than food. In the second half of the 20th century, technologies for recording the activity of muscles (EMG), brain (EEG) and eyes (EOG) were developed, after which it was possible to formulate ideas about the structure of sleep and its nature, which no one has yet refuted .
Sleep is a specific state of the nervous system with characteristic features and cycles of brain activity. Cyclicity is inherent in many natural phenomena. Cyclicity underlies our existence, ordered by the rhythmic change of day and night, seasons, work and rest. At the level of the organism, cyclicity is represented by biological rhythms, primarily the so-called circadian rhythms, caused by the rotation of the Earth around its axis.
Types of sleep. Sleep is called monophasic when the period of wakefulness and sleep is confined to the daily cycle of day and night. The daily sleep of an adult, as a rule, is monophasic, sometimes diphasic (twice a day); in a small child, a polyphasic type of sleep is observed, when the alternation of sleep and wakefulness occurs several times a day.
In nature, seasonal sleep (animal hibernation) is also observed, due to environmental conditions unfavorable for the body: cold, drought, etc. All of the listed types of sleep can be conditionally defined as natural or naturally caused.
Along with this, there are the following “unnatural” types of sleep: narcotic, hypnotic and pathological. Narcotic sleep can be caused by chemical influences: inhaling vapors of ether, chloroform, introducing tranquilizers, alcohol, morphine and some other substances into the body. This sleep can also be induced by electronarcosis (exposure to an intermittent low-intensity electric current).
Pathological sleep occurs with brain anemia, brain injury, the presence of tumors in the cerebral hemispheres, or damage to certain areas of the brain stem. This also includes lethargic sleep, which sometimes occurs as a reaction to severe emotional trauma and can last from several days to several years. The phenomena of pathological sleep should also include sleepwalking (somnambulism), the physiological mechanisms of which are still unknown.
Hypnotic sleep can be caused by the hypnotic effect of the environment and/or special influences of the person (the hypnotist). During hypnotic sleep, voluntary self-regulation is switched off while maintaining partial contact with others and the ability for sensorimotor activity. It should be noted that there are significant individual differences in the ability to perceive hypnotic suggestions or influences.
Disturbances in the rhythm of sleep are often observed, which include insomnia and the so-called irresistible sleep (narcolepsy), which occurs during passive driving, when performing monotonous work, as well as when driving vehicles.
The alternation of sleep and wakefulness is observed at all stages of the evolutionary ladder: from lower vertebrates to humans. There is no doubt that such a universal organization of rhythmic alternation of activity and rest has a deep physiological meaning. It is well known that during sleep, significant physiological changes occur in the functioning of the central nervous system, the autonomic nervous system and in other systems and functions of the body.
Stages of sleep. Human sleep is rhythmic and has a regular cyclic organization. There are five stages of sleep. Four stages of slow wave sleep and one stage of rapid wave sleep. It is sometimes said that sleep consists of two phases: slow and fast sleep. A completed cycle is considered to be a period of sleep in which there is a sequential change from the stages of slow-wave sleep to rapid sleep. Based on these provisions, V.M. Kovalzon offers the following definition of sleep: “sleep is a special genetically determined state of the human body (and warm-blooded animals, i.e. mammals and birds), characterized by a natural sequential change of certain polygraphic patterns in the form of cycles, phases and stages” (Kovalzon, 1993).
Sleep studies are carried out through polygraphic recording of physiological indicators. Using EEG recording, significant differences were revealed both between the stages of sleep and between the states of sleep and wakefulness. Based on a comprehensive study of sleep using EEG, EMG, ECG, EOG and pneumography (see Chapter 2), U. Cement and N. Kleitman in 1957 proposed a sleep pattern that has become classic. Eight to nine hour sleep is divided into five to six cycles, interspersed with short intervals of awakening, which, as a rule, do not leave any memories for the sleeper. Each cycle includes two phases: the phase of slow (orthodox) sleep and the phase of rapid (paradoxical) sleep.
First stage is a transition from the state of wakefulness to sleep. It is accompanied by a decrease in alpha activity and the appearance of low-amplitude oscillations of various frequencies. At the end of this stage, short bursts of so-called sleep spindles may appear, clearly visible against the background of slow-wave activity. However, until the sleep spindles reach a duration of 0.5 s. This period is considered the first stage of sleep. In behavior, this stage corresponds to the period of drowsiness. It may be associated with the birth of intuitive ideas that contribute to the success of solving a particular problem (see Chapter 11).
Second stage occupying slightly less than half of all night sleep, is called the “sleep spindle” stage, because its most striking feature is the presence in the EEG of fusiform rhythmic activity with an oscillation frequency of 12–20 Hz. The duration of these “spindles,” which are clearly distinguished from the background high-amplitude EEG with a mixed frequency of oscillations, ranges from 0.2 to 0.5 s.
Third stage is characterized by all the features of the second stage, to which is added the presence in the EEG of slow delta oscillations with a frequency of 2 Hz or less, occupying from 20 to 50% of the recording epoch. This transition period lasts only a few minutes. As sleep deepens, the spindles gradually disappear.
Fourth stage is characterized by a predominance in the EEG of slow delta oscillations with a frequency of 2 Hz or less, occupying more than 50% of the recording epoch of night sleep. The third and fourth stages are usually combined under the name delta sleep. Deep stages of delta sleep are more pronounced at the beginning and gradually decrease towards the end of sleep. At this stage, it is quite difficult to wake a person. It is at this time that about 80% of dreams occur, and it is at this stage that attacks of sleepwalking and nightmares are possible, but the person remembers almost none of this. The first four slow-wave stages of sleep normally occupy 75–80% of the total sleep period.
Fifth stage of sleep. The fifth stage of sleep has a number of names: the stage of “rapid eye movements” or abbreviated as REM, REM sleep (from English, rapid eye movements), “rapid eye movements”, “paradoxical sleep”. During this stage, the person is completely motionless due to a sharp drop in muscle tone. However, the eyeballs under closed eyelids make rapid movements with a frequency of 60–70 times per second. Moreover, there is a clear connection between rapid eye movements and dreams.
If you wake up a sleeping person at this time, then in approximately 90% of cases you can hear a story about a vivid dream, and the accuracy of the details will be significantly higher than when waking up from slow-wave sleep.
In particular, healthy people have more of these movements than patients with sleep disorders. It is typical that people who are blind from birth dream only of sounds and sensations. Their eyes are motionless. At one time it was believed that the intensity of REM sleep could be used to judge the vividness and emotional richness of dreams. However, eye movements during sleep differ from those characteristic of viewing objects while awake.
In addition, at this stage of sleep, the electroencephalogram acquires signs characteristic of the waking state (low-amplitude, high-frequency components predominate in the spectrum). The name “paradoxical” stage arose due to the apparent discrepancy between the state of the body (complete rest) and brain activity.
The paradoxical stage of sleep occurs in many mammal species. It was also noted that in animals the proportion of paradoxical sleep tends to increase with increasing degree of cortical development. However, paradoxical sleep occurs differently in animals and humans. If in humans only the eyes move, in animals there are movements of the limbs, as well as blinking, sucking movements, and sometimes they make sounds.
Periods of REM sleep occur at approximately 90-minute intervals and last on average about 20 minutes. In normal adults, this stage of sleep takes up approximately 20–25% of the time spent asleep. In infants this proportion is significantly higher; in the first weeks of life, about 80% of sleep time is paradoxical sleep, and in two years only 30%.
Need for sleep. This vital need depends on age. Thus, the total sleep duration of newborns is 20 - 23 hours a day, at the age of 6 months to 1 year - about 18 hours, at the age of 2 to 4 years - about 16 hours, at the age of 4 to 8 years 12 hours, from 8 to 12 years 10 hours, from 12 to 16 years 9 hours. Adults sleep on average 7 – 8 hours a day.
On average, in adults, the percentage ratio between all stages of sleep is:
Stage I (drowsiness) takes up an average of 5–10%
Stage II (sleepy spindles) – 40 – 45%
Stages III and IV (delta sleep) – 20 – 30%
Stage V (paradoxical sleep) – 15 – 25%
There is an opinion that the need for sleep decreases with old age. However, it has been found that people over 60 years of age who suffer from various diseases usually sleep less than 7 hours a day. At the same time, practically healthy people of this age sleep more than 8 hours a day. With an increase in sleep duration, older people who sleep little experience an improvement in their well-being. According to some data, the sleep duration of Caucasian centenarians ranges from 9 to 16 – 17 hours a day. On average, long-livers sleep 11–13 hours. In other words, as a person ages, the duration of sleep should increase.
A person deprived of sleep dies within two weeks. Sleep deprivation for 3 to 5 days causes an irresistible need for sleep. As a result of 60 - 80 hours of sleep deprivation, a person experiences a decrease in the speed of mental reactions, mood deteriorates, disorientation in the environment occurs, performance sharply decreases, rapid fatigue occurs during mental work and less accuracy occurs. A person loses the ability to concentrate, various motor impairments (tremors and tics) may occur, hallucinations are possible, and sudden memory loss and slurred speech are sometimes observed. With longer sleep deprivation, psychopathy and even paranoid mental disorders can occur.
Changes in autonomic functions during prolonged insomnia are very small; there is only a slight decrease in body temperature and a slight slowdown in heart rate.
Science has described several cases of prolonged lack of sleep, which, along with the phenomena of somnambulism (sleepwalking) and lethargic sleep, have not yet been explained. Most often, these cases were associated with severe mental shocks (loss loved one, consequences of the disaster). However, in most cases, such events lead to the opposite result - to lethargic sleep.
Slow and paradoxical sleep are equally necessary for the body. So, if you wake a person every time a paradoxical sleep occurs, the tendency to fall into a paradoxical sleep will increase. After a few days, the person will move from wakefulness to paradoxical sleep without an intermediate phase of normal sleep.
Thus, the stages of sleep form a unique system in which an impact on one link entails a change in the state of another link.
Physiological changes during sleep. The most characteristic symptoms of sleep include a decrease in the activity of the nervous system and cessation of contact with the environment due to the “switching off” of the sensorimotor sphere.
The thresholds of all types of sensitivity (vision, hearing, taste, smell and touch) increase during sleep. The threshold value can be used to judge the depth of sleep. In the first four stages, perception thresholds increase by 30–40%, while in REM sleep - by 400%. Reflex function during sleep is sharply weakened. Conditioned reflexes are inhibited, unconditioned reflexes are significantly reduced. However, some types of cortical activity and reactions to certain stimuli may persist during normal periodic sleep. For example, a sleeping mother hears the sounds of a sick child moving. This phenomenon is called partial wakefulness.
Most muscles are in a relaxed state during sleep, and a person is able to maintain a certain body position for a long time. At the same time, the tone of the muscles that close the eyelids, as well as the annular muscle that locks the bladder, is increased. As you fall into sleep, the heart and breathing rhythms slow down, becoming more and more uniform.
Slow-wave sleep is accompanied by a decrease in autonomic tone. As a result of the predominance of parasympathetic influences, the pupils narrow, the skin turns pink, sweating increases, salivation decreases, and the activity of the cardiovascular, respiratory, digestive and excretory systems, the volume of circulating blood decreases; there is excessive blood filling of the pulmonary vessels; the respiratory rate decreases, which leads to a limitation of the volume of oxygen entering the blood and a slower removal of carbon dioxide, i.e. the intensity of pulmonary gas exchange decreases. This is why the heart rate decreases at night, and with it the speed of blood flow.
It should be emphasized that, although in general the level of metabolism decreases during sleep, at the same time the processes of restoring the functionality of all cells of the body are activated, their reproduction is intensive, and proteins are replaced.
In contrast, during paradoxical sleep, a “vegetative storm” occurs. Breathing becomes irregular and changes in depth. Stopping breathing is also possible (for example, in a nightmare). Cerebral blood flow increases, heart rate may increase, and fluctuations in blood pressure are observed. In men at this stage, an erection of the penis may occur, in women - an erection of the clitoris, and not only in adults, but also in children. During REM sleep, a person loses the ability to regulate body temperature through shivering and sweating.
Throughout the night, the growth of hair and nails is activated in a person. A person's body temperature decreases during sleep (in women it drops to 35.6, and in men to 34.9 degrees). Similar daily temperature fluctuations - a decrease at night and an increase during the day - are also observed in the absence of sleep or during daytime sleep and night wakefulness.
In some forms of so-called hypnotic sleep, and in particular in catalepsy (catalepsy is the freezing of a person in the position he has adopted, sometimes even very uncomfortable, requiring significant muscle tension), a sharp increase in muscle tone occurs.
Dream theories
The first ideas about the origin of sleep are mainly of historical interest. So, in accordance with the hemodynamic theory, sleep occurs as a result of stagnation of blood in the brain when the body is in a horizontal position. According to another version, sleep is the result of anemia of the brain and at the same time its rest. According to the histological theory, sleep occurs as a result of disruption of connections between nerve cells and their processes, which occurs due to prolonged excitation of the nervous system.
Chemical theory. According to this theory, during wakefulness, easily oxidized products accumulate in the cells of the body, resulting in oxygen deficiency, and the person falls asleep. According to psychiatrist E. Claparède, we fall asleep not because we are poisoned or tired, but so as not to be poisoned and tired.
Histological analysis of the brains of dogs sacrificed after ten days without sleep shows changes in the shape of the pyramidal neuron nuclei of the frontal cortex. In this case, the blood vessels of the brain are surrounded by leukocytes and are torn in places. However, if the dogs are allowed to sleep a little before being killed, no changes are detected in the cells.
According to some assumptions, these changes are caused by a special poison, hypnotoxin. The composition, prepared from the blood, cerebrospinal fluid or extract of brain matter from dogs that had not slept for a long time, was injected into awake dogs. The latter immediately showed all signs of fatigue and fell into deep sleep. The same changes appeared in their nerve cells as in dogs that had not slept for a long time. However, it was never possible to isolate hypnotoxin in its pure form. Moreover, this theory is contradicted by P.K. Anokhin’s observations of two pairs of Siamese twins with common system blood circulation If sleep is induced by substances carried in the blood, then the twins should fall asleep at the same time. However, in such pairs, situations are possible when one head is asleep and the other is awake.
Chemical theory also cannot answer a number of questions. For example, why does daily poisoning with fatigue products not cause any harm to the body? What happens to these substances during insomnia? Why does a newborn baby sleep almost all the time?
Sleep as inhibition. According to I.P. Pavlov, sleep and internal inhibition, by their physical and chemical nature, are a single process. The difference between them is that internal inhibition in a waking person covers only certain groups of cells, while during the development of sleep, inhibition widely radiates throughout the cerebral cortex, spreading to the underlying parts of the brain. Such diffuse inhibition of the cortex and subcortical centers ensures their restoration for subsequent activities. I.P. Pavlov called sleep that develops under the influence of inhibitory conditioned stimuli active, contrasting it with passive sleep that occurs when the influx of afferent impulses into the cerebral cortex is stopped or sharply limited.
Modern ideas about the nature of sleep. Currently, most existing hypotheses regarding functional significance sleep and its individual stages can be reduced to three main approaches: 1) energetic or compensatory-restorative, 2) informational, 3) psychodynamic.
According to the first, in a dream the energy expended during wakefulness is restored. A special role is given to delta sleep, the increase in duration of which follows physical and mental stress. Any load is compensated by an increase in the proportion of delta sleep. It is at the delta stage of sleep that the secretion of neurohormones that have an anabolic effect occurs.
Morphological formations related to sleep regulation are identified. Thus, the reticular formation controls the initial stage of sleep. The hypnogenic zone, located in the anterior part of the hypothalamus, also has a regulatory effect on the functions of sleep and wakefulness. Peripheral hypnogenic zones are located in the walls of the carotid arteries. So, there are a number of hypnogenic zones in the body. The mechanism of sleep onset and awakening from sleep is complex and probably has a certain hierarchy.
PC. Anokhin attached decisive importance to the functions of the hypothalamus in this process. With prolonged wakefulness, the level of vital activity of the cells of the cerebral cortex decreases, so their inhibitory effect on the hypothalamus weakens, which allows the hypothalamus to “turn off” the activating effect of the reticular formation. When the upward flow of excitation decreases, the person falls asleep.
Information approach assumes that sleep is the result of a decrease in sensory influx to the reticular formation. The latter entails the inclusion of inhibitory structures. The point of view has also been expressed that it is not cells, not tissues, not organs that need rest, but mental functions: perception, consciousness, memory. The perceived information can “overwhelm” the brain, so it needs to disconnect from the outside world (which is the essence of sleep) and switch to a different operating mode. Sleep is interrupted when the information is recorded and the body is ready for new experiences.
In the context of the information approach, crucial importance is attached to the concept of synchronization in the work of brain structures. When tired, synchronization is disrupted. The standard for creating optimal coherence of rhythms is the “model of the required biorhythmic background”, created during wakefulness on the basis of the innate behavior program and signals coming from outside.
To create this model, external information is needed. Dreams perhaps reflect this process of regulating biorhythmic relationships between brain structures. At the same time, it is possible that in REM sleep the activity of those neurons that functioned during the day is activated. Therefore, in order to comply with the biorhythmic background, they are forced to actively work in REM (Wayne, 1991).
The hypothesis of I.N. is also formulated in the logic of the information approach. Pigareva (1994). According to this theory, the brain continues to perform its usual information processing activities during sleep. At the same time, those brain structures that process information coming from the senses while awake are tuned in a dream to perceive and process information coming from the internal organs.
According to the famous psychoneurologist A.M. Wein (1991), the information approach does not contradict the energy concept of restoration, because the processing of information in a dream does not replace processing during wakefulness, but complements it. Recovery in the broadest sense of the word is not rest and passive accumulation of resources, but, first of all, a kind of brain activity aimed at reorganizing perceived information.
Psychodynamic approach illustrates the theory of A.M. Wein (1991), according to which there is a hierarchically constructed, integral brain system that regulates the cycles of sleep and wakefulness. It includes: the reticular activating system, which maintains the level of wakefulness; synchronizing apparatuses responsible for slow-wave sleep, and the reticular nuclei of the pons, responsible for REM sleep. There is a dynamic interaction between these structures, the result of which determines the final direction of the body’s state - towards wakefulness or sleep. In the same system, the direction of the body’s state is coordinated with the activity of the autonomic and somatic systems, and receives its equivalent in the form of a subjectively experienced mental state.
Ideas about the nature of REM sleep. There are a number of theories and hypotheses about the nature and meaning of paradoxical sleep. Unlike slow-wave sleep, REM sleep has a pronounced active nature. Paradoxical sleep is triggered from a clearly defined center located at the back of the brain, in the region of the pons and medulla oblongata. During this stage of sleep, brain cells are extremely active, but the process of transmitting information from the senses to the brain centers, and from them to the muscular system, is blocked.
Some researchers believe that these are periods of cell restoration, others believe that REM sleep acts as a “safety valve”, allowing excess energy to be discharged while the body is completely deprived of movement; according to others, REM sleep helps to consolidate in memory information received during wakefulness. Some studies even indicate a close connection between a high level of intellectual development and a long total duration of periods of paradoxical sleep in many people.
Jouvet's hypothesis looks very attractive, according to which, in REM sleep, hereditary, genetic information related to the organization of holistic behavior is transmitted to neurological memory.
REM sleep itself can be divided into two stages. Against the background of continuous desynchronization, lasting from 5 to 20 seconds and accompanied by rapid eye movements, the rapid development of the tetrarhythm generated by the hippocampus begins. This is the emotional stage of REM sleep. Then the theta rhythm weakens, and meanwhile in the new cortex, especially in its sensorimotor area, the alpha rhythm increases. Then the alpha rhythm weakens, and the theta rhythm increases again in the hippocampus. Both stages alternate several times during sleep, with the first always longer than the second. An increase in the theta rhythm in REM sleep is accompanied by the same vegetative phenomena that accompany intense wakefulness, saturated with strong emotions.
In general, we can conclude that the main function of slow-wave sleep is to restore the homeostasis of brain tissue and optimize the control of internal organs. It is also well known that sleep is essential for restoring physical strength and optimal mental state. As for paradoxical sleep, it is believed that it facilitates long-term storage of information and its reading.
Psychophysiology of stress
Stress is often considered as a special functional state and at the same time as a psychophysiological reaction of the body to environmental influences that go beyond the boundaries of the adaptive norm. The term "stress" was coined by Hans Selye in 1929. As a medical student, he noticed that all patients suffering from a variety of diseases experience a number of common symptoms (loss of appetite, muscle weakness, elevated blood pressure and temperature, loss of motivation to achieve). Since these symptoms do not depend on the nature of the somatic disorder, Selye proposed to designate this condition as a “simply disease syndrome.” Selye originally used the term “stress” to describe the totality of all nonspecific changes (within the body), functional or organic. One of his latest definitions of stress is: “a nonspecific reaction of the body to any external demand” (Selye, 1974).
Currently, the term stress is used to refer to a number of phenomena:
1) strong, unfavorable, negatively affecting the body;
2) a strong physiological or psychological reaction to the action of a stressor that is unfavorable for the body;
3) strong, both favorable and unfavorable reactions of various kinds for the body;
4) nonspecific features (elements) of physiological and psychological reactions of the body under strong, extreme influences on it, causing intense manifestations of adaptive activity;
5) nonspecific features (elements) of physiological and psychological reactions of the body that arise during any reactions of the body.
Thus, in general, stress is a nonspecific component of adaptation that plays a mobilizing role and determines the attraction of energy and plastic resources for adaptive restructuring of the body.
Types of stress. Selye believed that the stress reaction is a nonspecific set of psychophysiological changes that does not depend on the nature of the factor that provokes stress. Later, however, it was shown that the general pattern of psychological reactions can be very specific. Both the qualitative originality of the stimulus and the individual characteristics of the organism contribute to its formation.
In connection with the characteristics of the stimulus, it is customary to distinguish at least two types of stress: physical (physiological, primary signal) and psychoemotional (secondary signal).
The stimulus that causes a stress response is called a stressor. A stimulus can become a stressor as a result of its cognitive interpretation, i.e. the meaning that a person attributes to a given stimulus (psycho-emotional stress). For example, the sound of someone else's footsteps behind a person walking down the street at night on a deserted street can be a strong stressor. Physical stress results from exposure to a stimulus through some sensory or metabolic process. For example, suffocation or too much physical exertion become stressors that provoke physiological stress. The special role of the duration of exposure to an unfavorable factor should be emphasized. Thus, some irritants can cause a stress reaction as a result of their exposure to a person for a sufficiently long time. In the event of short-term stress, as a rule, already established response and resource mobilization programs are updated.
Introduction
What is sleep, why does the body need it? The question of the functional purpose of such an ordinary state seems so naive that it does not even require thought: of course, for relaxation! However, such an answer gives rise to a chain of new questions: what is rest? Why is it so long and so complexly organized? Why is it confined to certain periods of the day? Why is bodily rest not enough for rest, but it is also necessary to turn off the senses, which, it would seem, sharply increases vulnerability to unfavorable environmental factors? Why are warm-blooded animals, for whom “constancy of the internal environment is the key to free life,” forced, like their cold-blooded ancestors, to fall into a state of immobility and unresponsiveness for several hours every day?
For many centuries, sleep was considered precisely by these external signs, that is, a state of rest and reduced reactivity. This approach could not be prevented even by the formation of ideas about two states “within” natural sleep, fundamentally different from each other and from wakefulness (slow wave and paradoxical phases). However, recently an increasing number of facts have appeared that do not fit into such ideas. So, in the early 80s, employees of the First Moscow Medical Institute V.S. Rotenberg and S.I. Kobrin, studying the sleep of patients with complete atrophy of the muscular system, did not reveal its reduction, although these patients did not at all need somatic (bodily) “rest”. This means that sleep is not rest, and bodily rest is not at all an obligatory element of physiological sleep.
In a similar way, we can consider such a generally accepted characteristic of sleep as unresponsiveness, that is, mental retardation, lack of response to external stimuli. Firstly, this is an “a posteriori” sign of sleep, since the threshold for awakening can only be determined by waking up the person. Secondly, unresponsiveness, like immobility, is not a sufficient sign, since it is characteristic of a number of diseases and other pathological conditions: pharmacological sleep, anesthesia, coma, and others.
1. The nature of sleep
1.1 Dream theories
The humoral theory considers substances that appear in the blood during prolonged wakefulness as the cause of sleep. The proof of this theory is an experiment in which a awake dog was transfused with the blood of an animal that had been deprived of sleep for 24 hours. The recipient animal immediately fell asleep. Currently, it has been possible to identify some hypnogenic substances, for example, a peptide that induces delta sleep. But humoral factors cannot be considered as the absolute cause of sleep. This is evidenced by observations of the behavior of two pairs of unseparated twins. Their nervous system was completely separated, and their circulatory systems had many anastomoses. These twins could sleep in different time: one girl, for example, could be asleep, while the other was awake.
Reticular theory of sleep and wakefulness. The reticular formation of the brainstem contains many neurons, the axons of which go to almost all areas of the brain (except the neocortex). In the late 1940s, Moruzzi and Magoon discovered that high-frequency stimulation of the reticular formation of the brain stem of cats causes them to instantly awaken. Damage to the reticular formation causes constant sleep, but cutting the sensory tracts does not have this effect. The reticular formation began to be considered as an area of the brain involved in maintaining sleep. Sleep occurs when its activity either passively or under the influence of external factors decreases. Activation of the reticular formation depends on the number of sensory impulses entering it, as well as on the activity of descending fibers between the forebrain and brainstem structures. However, it was later found that: the reticular formation causes not only wakefulness, but also sleep, which depends on the location of the electrodes when stimulated by an electrical stimulus; the neural state of the reticular formation in the waking state and during sleep differs little; the reticular formation is not the only center of wakefulness: they are also represented in the medial thalamus and the anterior hypothalamus.
Serotonergic theory of sleep and wakefulness. Two regions are found in the upper brainstem: the raphe nucleus and the locus coeruleus. The mediator in the cells of the tent nucleus is serotonin, and the locus coeruleus is norepinephrine. In the late 1960s, Jouvet came to the conclusion that these two neural systems are involved in the occurrence of sleep. Destruction of the raphe nuclei in a cat leads to complete insomnia for several days; sleep is restored over the next few weeks. Partial insomnia can be caused by the suppression of serotonin synthesis by chlorphenylalanine; administration of a serotonin precursor can eliminate it. Destruction of the locus coeruleus leads to the complete disappearance of REM sleep, but does not affect slow-wave sleep. Depletion of serotonin stores causes insomnia, and the introduction of serotonin precursors normalizes only slow-wave sleep. All this suggested that serotonin leads to inhibition of structures responsible for wakefulness. It was found that the locus coeruleus suppresses the impulses of the raphe nucleus, and this leads to awakening.
It has now been proven that the neurons of the raphe nuclei secrete serotonin during wakefulness: it serves as a mediator in the process of awakening and a “sleep hormone” in the waking state: stimulating the release of the sleep substance, which causes sleep. REM sleep is mediated by the subcoeruleus nucleus. It has been shown that sleep and wakefulness are determined by the activation of specific centers in the brain. One of these centers is the reticular formation, which is located in the brain stem. One of the main components of the reticular formation are the cholinergic nuclei located at the level of the mesencephalon-pontine articulation. The neurons of these nuclei have a high level of activity during wakefulness and the REM phase and are inactivated during slow-wave sleep.
Other ergic systems of the brain also take part in the regulation of sleep-wake processes, the mediators of which are: serotonin, norepinephrine, histamine, glutamate, vasopressin. It is likely that dyssomnia is caused by dysfunction of neurotransmitter systems.
Subcortical and cortical theories of sleep: with various tumor or infectious lesions of the subcortical, especially stem, formations of the brain, patients experience various sleep disorders - from insomnia to prolonged lethargic sleep, which indicates the presence of subcortical sleep centers. When the posterior structures of the subthalamus and hypothalamus were irritated, the animals fell asleep, and after the irritation stopped, they woke up, which indicates the presence of sleep centers in these structures. In the laboratory of I.P. Pavlov found that with prolonged development of fine differentiation inhibition, animals often fell asleep. Therefore, the scientist considered sleep as a consequence of the processes of internal inhibition, as a deepened, diffuse inhibition that spread to both hemispheres and the nearest subcortex (cortical theory of sleep).
However, a number of facts could not be explained by either the cortical or subcortical theories of sleep. Observations of patients who lacked almost all types of sensitivity showed that such patients fall into a state of sleep as soon as the flow of information from the operating sense organs is interrupted. For example, in one patient, of all the sense organs, only one eye was preserved, the closure of which plunged the patient into a state of sleep. Many questions of the organization of sleep processes were explained with the discovery of the ascending activating influences of the reticular formation of the brain stem on the cerebral cortex. It has been experimentally proven that sleep occurs in all cases of elimination of the ascending activating influences of the reticular formation on the cerebral cortex. Descending influences of the cerebral cortex on subcortical formations were established. In the waking state, in the presence of ascending activating influences of the reticular formation on the cerebral cortex, neurons of the frontal cortex inhibit the activity of neurons in the sleep center of the posterior hypothalamus. In a state of sleep, when the ascending activating influences of the reticular formation on the cerebral cortex decrease, the inhibitory influences of the frontal cortex on the hypothalamic sleep centers decrease.
There are reciprocal relationships between the limbic-hypothalamic and reticular structures of the brain. When the limbic-hypothalamic structures of the brain are excited, inhibition of the structures of the reticular formation of the brain stem is observed and vice versa. When awake, due to the flow of afferentation from the sensory organs, the structures of the reticular formation are activated, which have an ascending activating effect on the cerebral cortex. In this case, neurons of the frontal cortex exert descending inhibitory influences on the sleep centers of the posterior hypothalamus, which eliminates the blocking influence of the hypothalamic sleep centers on the reticular formation of the midbrain. With a decrease in the flow of sensory information, the ascending activating influences of the reticular formation on the cerebral cortex decrease. As a result, the inhibitory effects of the frontal cortex on the neurons of the sleep center of the posterior hypothalamus are eliminated, which begin to inhibit the reticular formation of the brain stem even more actively. Under conditions of blockade of all ascending activating influences of subcortical formations on the cerebral cortex, a slow wave stage of sleep is observed.
Hypothalamic centers, due to connections with limbic structures of the brain, can have ascending activating influences on the cerebral cortex in the absence of influences from the reticular formation of the brain stem. These mechanisms constitute the cortical-subcortical theory of sleep (P.K. Anokhin), which made it possible to explain all types of sleep and its disorders. It proceeds from the fact that the state of sleep is associated with the most important mechanism - a decrease in the ascending activating influences of the reticular formation on the cerebral cortex. The sleep of cortical-free animals and newborn children is explained by the weak expression of the descending influences of the frontal cortex on the hypothalamic sleep centers, which under these conditions are in an active state and have an inhibitory effect on the neurons of the reticular formation of the brain stem.
A newborn's sleep is periodically interrupted only by the excitation of the hunger center located in the lateral nuclei of the hypothalamus, which inhibits the activity of the sleep center. In this case, conditions are created for the entry of ascending activating influences of the reticular formation into the cortex. This theory explains many sleep disorders. Insomnia, for example, often occurs as a result of overexcitation of the cortex under the influence of smoking or intense creative work before bedtime. At the same time, the descending inhibitory influences of frontal cortex neurons on the hypothalamic sleep centers are enhanced and the mechanism of their blocking effect on the reticular formation of the brain stem is suppressed. Prolonged sleep can be observed when the centers of the posterior hypothalamus are irritated by a vascular or tumor pathological process. Excited cells of the sleep center continuously exert a blocking effect on the neurons of the reticular formation of the brain stem.
Sometimes during sleep, so-called partial wakefulness is observed, which is explained by the presence of certain channels of reverberation of excitations between the subcortical structures and the cerebral cortex during sleep against the background of a decrease in the ascending activating influences of the reticular formation on the cerebral cortex. For example, a nursing mother may sleep soundly and not respond to strong sounds, but she quickly wakes up even when the baby moves slightly. In the case of pathological changes in a particular organ, increased impulses from it can determine the nature of dreams and be a kind of harbinger of a disease, the subjective signs of which are not yet perceived in the waking state.
Differential theory of sleep and wakefulness. In the late 1930s, Bremer discovered that the EEG of a cat with a transection separating the spinal cord from the brain after recovery from surgical shock showed cyclic alternations characteristic of sleep-wakefulness. If the transection is made at the level of the quadrigeminal, that is, sensory stimuli other than visual and olfactory are excluded, an EEG typical for sleep is observed. Bremer concluded that the central nervous system is induced and maintained: wakefulness requires a minimum of sensory stimulation, sleep is a state characterized primarily by a decrease in the effectiveness of sensory stimulation of the brain, which confirms the theory of passive wakefulness.
However: firstly, in the isolated forebrain over time, rhythmic fluctuations characteristic of the sleep-wake rhythm appear. In addition, isolating a person in a soundproof chamber leads to a decrease in sleep duration. Secondly, the data on the influence of the cortex on the state of wakefulness are incorrect, since circadian sleep-wake rhythms are also observed in newborn children with aencephalics.
Endogenous theory of sleep. A person feels a certain need for sleep, which is associated with the presence of sleep factors circulating in the blood. Then their normal concentrations should be restored during sleep. It is hypothesized that sleep factors accumulate during wakefulness to sleep-inducing levels. According to another hypothesis, these factors accumulate during sleep: they are formed and released. A glycopeptide, delta peptide, was isolated from urine and cerebrospinal fluid and induces slow-wave sleep when administered to other animals. There is also a factor of REM sleep. The second hypothesis led to the discovery of delta sleep peptide in the blood, which induces deep sleep.
However, the factors found cause sleep in humans and only in some animal species. In addition, it can also occur under the influence of other types of substances. To date, it is unknown what physiological role the found factors play in the process.
Pharmacological sleep is not adequate in its mechanisms to natural sleep. Sleeping pills limit the activity of various brain structures - the reticular formation, the hypothalamic region, and the cerebral cortex. This leads to disruption of the natural mechanisms of formation of sleep stages, disruption of the process of memory consolidation, processing and assimilation of information.
1.2 I.P. Pavlov and the nature of sleep
It is known that Pavlov was extremely interested in the problem of sleep and considered it one of the key ones in the study of higher nervous activity. Everyone knows his definition of sleep as “diffused cortical inhibition.” After the discovery of the paradoxical dream, it seemed that Pavlov’s theory in this part was hopelessly outdated. However, in fairness, it should be recalled that the idea of three forms of existence - wakefulness, quiet sleep and dream sleep - was first heard in the Upanishads, an ancient Indian epic. In the history of European culture, this seems to have never occurred to anyone before Jouvet. Even the discoverers of paradoxical sleep - N. Kleitman, Yu. Azerinsky and V. Dement called this state stage-1-REM, that is, the stage of falling asleep (drowsiness) with rapid eye movements, perceiving it only as a transition between wakefulness and sleep!
If we take slow wave (orthodox) sleep, sleep in general, then now, at the turn of the century, it is appropriate to ask the question: was Pavlov so wrong in his ideas about sleep? Of course, in that “pre-electrophysiological” era, these ideas could only be purely intuitive. But the reader of this article, knowing about the powerful activation of inhibitory neurons and the release of their mediators - GABA and adenosine in slow-wave sleep, about the activation that begins in local thalamocortical areas and gradually spreads throughout the system, about tonic hyperpolarization as a period of a kind of functional recovery of neurons, etc. .p., has the right to judge for himself whether the intuition failed this time of the brilliant scientist. At the end of his long life, in 1935, Pavlov expressed the following thought: “It is clear that our daily work represents a sum of irritations, which determines a certain amount of exhaustion, and then this sum of exhaustion, reaching the end, causes automatically, by internal humoral means , an inhibited state accompanied by sleep.” This formulation can be called prophetic - it sounds quite relevant today.
2. Physiology of sleep
2.1 Sleep phases
The appearance of electroencephalography in the second half of the 20th century. finally made it possible to strictly distinguish the phases of sleep and thereby approach the clarification of their physiological role. Since physiologists identify sleep, its phases and stages on the basis of generally accepted, so-called polygraphic criteria, polygrams - electroencephalogram (EEG), electromyogram (EMG), electrooculogram (EOG), it is natural to determine the essence of sleep by these indicators. However, here we are faced with the same difficulties: there is not a single sign sufficient to determine sleep. Certain characteristics of slow-wave sleep and paradoxical sleep on the EEG are sometimes found in other conditions. Thus, in various forms of pathology and under the influence of pharmacological drugs, certain changes are observed on the EEG that “imitate” certain stages of sleep.
Most likely, rhythmicity can be considered a necessary and sufficient sign of sleep, that is, the alternation of certain physiological signs (printing patterns) that make it possible to distinguish normal sleep from monotonous “dream-like states.” Accordingly, the criterion for “normality” of sleep is the cyclic alternation of stages 1–2–3–4 of slow sleep, which ends with the paradoxical phase. Based on this approach, the modern definition of sleep is as follows: it is “a special genetically determined state of the human body (and warm-blooded animals, that is, mammals and birds), characterized by a natural sequential change of certain polygraphic patterns in the form of cycles, phases and stages.”
What lies behind this cyclical alternation? What is the purpose of each of the two stages of sleep? In physiology, to understand the functions of an individual organ, the classical method of destruction is used: if a given organ is damaged or removed, then, knowing the consequences and adequately interpreting them, one can find out its role. A similar approach is used in relation to sleep: do not let the test or experimental animal sleep for some time and see what changes in the body and behavior. Such experiments were first performed more than 100 years ago by the Russian scientist M.M. Manaseina (1843–1903), who essentially became the founder of the “science of sleep” - somnology.
In our century, experiments on animals and observations of healthy people have repeatedly tried to find out what sleep deprivation leads to. However, only with the use of electroencephalography such attempts received scientific justification. Studies in humans in recent years have yielded somewhat paradoxical results: deprivation for one or several days in the mildest, most gentle way did not lead to serious disorders in the body and psyche of the subjects. There was only increased drowsiness, fatigue, irritability, and absent-mindedness. It seemed that the main result of sleep deprivation was an increasing need for it! Naturally, such work on people cannot last more than 2–3 days; Therefore, the effects of long-term sleep deprivation are studied only in animal experiments.
Thus, in the 80s, a group of American specialists (A. Rechschaffen and co-workers) obtained fundamentally important results. As experiments have shown, if at the first signs of sleep on the EEG (the appearance of sleep spindles and delta waves) animals are awakened, then a temporary “fragmentation” of sleep occurs into very short periods and its spatial “localization”, when sleep occurs in separate areas of the brain. A similar phenomenon was described in experiments on monkeys by I.N. Pigarev (Institute for Information Transmission Problems, Russian Academy of Sciences), and L.M. Mukhametov and his colleagues (Institute of Ecology and Evolution named after A.N. Severtsov RAS) observed alternating unihemispheric slow-wave sleep in dolphins and eared seals. Comparing these results with some other data on chronic deprivation using physical methods, scientists came to an unexpected conclusion: it is in principle impossible to completely eliminate slow-wave sleep.
As experiments have shown, several weeks after the start of chronic deprivation in rats, the “pressure” of slow sleep decreased, and if deprivation stopped, then the “recoil” of slow sleep was not observed. It is clear that at first this “pressure” increases, and then, upon reaching a certain critical level, it subsides as a result of the gradual adaptation of the phenomena and structure of slow-wave sleep to conditions of deprivation.
Completely opposite results were obtained for paradoxical sleep. The experiments of Rechschaffen and his colleagues demonstrated that, no matter what type of sleep deprivation is carried out (total sleep deprivation, selective deprivation of the slow or paradoxical phase), the result is always a critical suppression of paradoxical sleep. Sooner or later it leads to the same dramatic consequences (change appearance, behavior and internal organs), which after a few “sleepless” weeks end in the inevitable death of the animals. It is characteristic, however, that the immediate cause of their death could not be discovered.
Interestingly, in rats there was a sharp drop in EEG amplitude after chronic deprivation, which occurred each time about a day before the death of the animal. If the experiment was stopped against this background, then the rat could no longer fall asleep and the EEG amplitude was not restored; death still occurred within 24 hours. Therefore, this drop in EEG amplitude indicated some kind of irreversible disruption of brain function caused by paradoxical sleep deprivation. If the experience stopped at a late stage of deprivation, but before this critical moment, then a powerful “recoil” of only paradoxical sleep was observed, regardless of what type of deprivation was used - deprivation of all sleep, paradoxical or slow sleep.
Thus, experiments with long-term sleep deprivation in laboratory animals once again show that sleep includes two fundamentally different states of the body - slow wave and paradoxical (fast) phases, confirming the brilliant guess of M. Jouvet, first expressed almost 40 years ago: “Who knows the secret of sleep, learns the secret of the brain.”
2.2 Sleep mechanisms
One of the main questions that has worried physiologists since the time of Pavlov is the existence of a “sleep center” in the brain. In the second half of our century, direct study of neurons involved in the regulation of sleep-wakefulness showed that the normal operation of the thalamocortical system of the brain, which ensures conscious human activity in wakefulness, is possible only with the participation of certain subcortical, so-called activating structures. Due to their actions in wakefulness, the membrane of most cortical neurons is depolarized by 10-15 mV compared to the resting potential - (65-70) mV. Only in a state of this tonic depolarization are neurons able to process information and respond to signals coming to them from other nerve cells (receptor and intracerebral).
As is now clear, there are several such systems of tonic depolarization, or brain activation (conventionally, “wakefulness centers”) – probably five or six. They are located at all levels of the cerebral axis: in the reticular formation of the brainstem, in the area of the locus coeruleus and dorsal raphe nuclei, in the posterior hypothalamus and the basal nuclei of the forebrain. The neurons of these sections secrete mediators - glutamic and aspartic acids, acetylcholine, norepinephrine, serotonin and histamine, the activity of which is regulated by numerous peptides located in the same vesicles. In humans, disruption of the activity of any of these systems is not compensated for by the others, is incompatible with consciousness and leads to coma.
It would seem that if there are “wakefulness centers” in the brain, then there should at least be one “sleep center.” However, in last years It turned out that the “wakefulness centers” themselves have a built-in positive feedback mechanism. These are special neurons that inhibit activating neurons and are themselves inhibited by them. Such neurons are scattered throughout different parts of the brain, although most of them are in the reticular part of the substantia nigra. They all secrete the same neurotransmitter - gamma-aminobutyric acid, the main inhibitory substance in the brain. As soon as the activating neurons weaken their activity, the inhibitory neurons turn on and weaken it even more. For some time, the process develops downward until a certain “trigger” is triggered and the entire system switches either to a state of wakefulness or paradoxical sleep. Objectively, this process reflects the change in patterns of electrical activity of the brain (EEG) during one full human sleep cycle (90 min).
Recently, the attention of researchers has been drawn to another evolutionarily ancient inhibitory system of the brain, which uses the nucleoside adenosine as a mediator. Japanese physiologist O. Hayaishi and colleagues showed that prostaglandin D2 synthesized in the brain is involved in the modulation of adenosinergic neurons. Since the main enzyme of this system, prostaglandinase-D, is localized in the meninges and choroid plexus, the role of these structures in the formation of certain types of sleep pathologies is obvious: hypersomnia in some traumatic brain injuries and inflammatory processes of the meningeal membranes, African “sleeping sickness” caused by trypanosomes , which is transmitted through the bites of tsetse flies, etc.
Direct recording of single activity of brain neurons in experiments on laboratory animals showed that in wakefulness (in a state of tonic depolarization) the nature of the discharges of thalamocortical cells is highly individual. But as sleep deepens and synchronized activity increases, more powerful inhibitory postsynaptic potentials begin to predominate in the EEG, interspersed with periods of exaltation - high-frequency bursts of neuronal discharges (this pattern of neural activity is called a “burst-pause”). Then “choral” activity of neurons appears, and the conditions for processing information in the brain, not only coming from the senses, but also stored in memory, sharply deteriorate. However, the average firing rate of cortical and thalamic neurons does not decrease, and in GABAergic (inhibitory) neurons it even increases significantly. As for the activating neurons, their discharges become less frequent. These neurophysiological phenomena correlate well with known data on the gradual inhibition of mental activity as slow-wave sleep deepens in humans.
If, from the point of view of neural activity, wakefulness is a state of tonic depolarization, then slow-wave sleep is tonic hyperpolarization. In this case, the direction of movement through the cell membrane of the main ion flows (Na+, K+, Ca2+ cations, Cl– anions), as well as the most important macromolecules, changes to the opposite.
Thus, one could say that during slow-wave sleep, brain homeostasis, disturbed during many hours of wakefulness, is restored. From this point of view, wakefulness and slow-wave sleep are like “two sides of the same coin.” Periods of tonic depolarization and hyperpolarization must periodically replace each other in order to maintain the constancy of the internal environment of the brain and ensure the normal functioning of the thalamocortical system - the substrate of higher mental functions of a person. From here it is clear why there is no single “slow sleep center” in the brain - this would significantly reduce the reliability of the entire system, making it more strictly determined, completely dependent on the “whims” of this center in the event of any disruption to its work.
On the other hand, it also becomes clear why long-term complete suppression of slow-wave sleep is almost impossible: normally, activity is periodically replaced by rest, and wakefulness is replaced by slow-wave sleep, which covers the entire brain. It is known that during artificial chronic deprivation, the mechanisms of wakefulness and slow-wave sleep begin to function diffusely and simultaneously. In this case, of course, normal behavior suffers, but, despite the deprivation effect, brain homeostasis is restored. However, everything is not so simple here either. Recently, Pigarev, in experiments on cats, showed that as synchronization in the EEG develops, the primary neurons of the visual and auditory cortex stop responding to specific stimuli and begin to increasingly respond to impulses coming to the cortex from the internal organs. Taking into account the discovered special Ca channels on the membrane of many cortical neurons, which open during hyperpolarization, it can be assumed that in slow-wave sleep the brain does not stop processing information, but moves from processing external signals to interoceptive impulses.
Thus, the function of slow-wave sleep seems to finally begin to emerge: it is the restoration of the homeostasis of brain tissue and the optimization of the control of internal organs. For sleep hygiene, this means confirmation of a rule as old as the world, but for some reason forgotten: without good night there can be no good wakefulness!
The situation is completely different with paradoxical sleep, which, unlike slow-wave sleep, has a pronounced active nature. Paradoxical sleep is triggered from a clearly defined center located in the back of the brain, in the area of the pons and medulla oblongata, and the mediators are acetylcholine, glutamic and aspartic acids. During paradoxical sleep, brain cells are extremely active, but information from the sensory organs does not reach them and is not sent to the muscular system. This is the paradox of this state.
Apparently, in this case, information received in previous wakefulness and stored in memory is intensively processed. According to Jouvet's hypothesis, in paradoxical sleep, although it is not yet clear how, hereditary, genetic information related to the organization of holistic behavior is transmitted to neurological memory. Confirmation of such mental processes is the appearance of emotionally charged dreams in humans in paradoxical sleep, as well as the phenomenon of the demonstration of dreams in experimental cats discovered by Jouvet and his colleagues and studied in detail by E. Morrison and his colleagues. They found that in the brain of cats there is a special area responsible for muscle paralysis during paradoxical sleep. If it is destroyed, experimental cats begin to show their dream: running away from an imaginary dog, catching an imaginary mouse, and so on. Interestingly, “erotic” dreams have never been observed in cats, even during the mating season.
Although in paradoxical sleep some neurons of the reticular formation of the brainstem and the thalamocortical system demonstrate a unique pattern of activity, differences between brain activity in wakefulness and paradoxical sleep could not be identified for a long time. This was done only in the 80s. It turned out that of all the known activating brain systems that turn on upon awakening and operate during wakefulness, only one or two are active in paradoxical sleep. These are systems located in the reticular formation of the brainstem and the basal ganglia of the forebrain, using acetylcholine, glutamic and aspartic acids as transmitters. However, other activating mediators (norepinephrine, serotonin and histamine) do not work in paradoxical sleep. This silence of monoaminoergic neurons in the brainstem determines the difference between wakefulness and paradoxical sleep, or at the psychic level, the difference between the perception of the external world and dreams. It was still unclear how this activation, so different from wakefulness, was reflected in the functioning of the cortex. Only in 1996–1997. Three independent studies revealed in paradoxical sleep (by positron emission tomography) a highly specific nature of the spatial distribution of activation and inactivation of certain areas of the cortex and some subcortical nuclei in the human brain.
2.3 Physiological significance of sleep
With prolonged total sleep deprivation of up to 116 hours, disorders of sleep, behavior, mental processes, affective sphere, and the appearance of hallucinations (especially visual) are observed. On the first recovery night, slow-wave sleep predominates, while the disappearance of paradoxical sleep was observed, but later there was a prolongation of PS and an increase in REM sleep.
With deprivation of paradoxical sleep, behavioral disturbances occur, fears and hallucinations appear, but the effect with deprivation of paradoxical sleep was less significant than with deprivation of slow-wave sleep. In the subjects who had dreams on the recovery night, there was no compensatory increase in PS. In subjects who experienced behavioral disorders, hallucinations, and so on, an increase in paradoxical sleep was observed. It was found that during sleep deprivation the concentration of delta peptide increases; its introduction into the thalamic zone caused an increase in slow-wave sleep and paradoxical sleep. The sleep factor also accumulates, which is used in immunological protection.
According to J. Oswald, slow sleep is needed to restore the functioning of brain cells. During sleep, growth hormone is released from the hypothalamus; it is involved in protein biosynthesis in peripheral tissues. The biosynthesis of proteins and RNA of neurons intensifies during paradoxical sleep. According to Labori, slow-wave sleep is associated with the metabolic activity of neuroglia.
J. Moruzzi distinguishes two types of restoration processes in nervous tissue:
a) fast processes: in neurons that perform the function of conducting and synaptic transmission of impulses, these processes last for several seconds, which can also take place during wakefulness, without interrupting the activity of the neuron itself - sleep is not needed for this;
b) slow processes are necessary for neurons whose synapses are subject to plastic changes during learning. Perception of all types of conscious life that are associated with higher functions. Sleep is not a period of restoration of the entire brain, but only a period of restoration of synapses with plastic properties.
Paradoxical sleep is associated with motivational functions: during dreams, needs are satisfied that were not achieved during wakefulness. During sleep, motivational energy is released, thereby maintaining the state of the body. In patients with endogenous depression, who are characterized by abnormal vivid dreams, motivational processes are strongly represented during sleep, which leads to a decrease in the severity of these processes during wakefulness. On the other hand, deprivation of REM sleep leads to the severity of motivational processes during wakefulness and reduces the severity of endogenous depression (Vogel). This is what the action of antidepressants is based on.
In 1958–1960, a pattern was discovered between sleep duration and mortality. Basically, both short sleepers (4–5 hours a day) and long sleepers (10–12 hours) die from cancer, coronary artery disease, and suicides are often committed. Thus, sleep has a restorative effect on both physical and mental health.
3. Sleep disorders
3.1 Insomnia. Narcolepsy. Hypersomnia
Insomnia and narcolepsy are hereditary diseases.
Narcolepsy is a disorder of wakefulness characterized by daytime episodes of irresistible sleep. It is associated with the fact that a person suffering from narcolepsy immediately falls from a state of wakefulness into a paradoxical sleep. Symptoms: uncontrollable falling asleep, muscle weakness. For many people, the circadian sleep-wake rhythm is disrupted. Weakness in the muscles appears due to anger, laughter, crying and other factors.
Hypersomnia is an unusual need for sleep, the cause of which is an imbalance in the sleep-wake regulation systems in the body.
We see in dreams various combinations of what happened to us while we were awake: in the cerebral cortex during shallow sleep or during the transition of sleep from one stage to another, when falling asleep, islands remain - uninhibited areas of the cortex, and under the influence of internal or external stimuli from them some information is “extracted”, events that happened to us in reality, which is the basis for the emergence of unreal reality.
During sleep, in our dreams, we see ourselves as sick, and after a few days we actually become sick; the fact is that in a dream we become more sensitive, we feel more acutely the processes that occur in our body, which we feel in reality.
Snoring: during sleep, the soft tissues of the back wall relax and sometimes block the airways (recession of the tongue - causes apnea - leads to death) Snoring is a sound generated by vibrations of soft tissue, especially the soft palate.
Conclusion
Sleep is a physiological state that is characterized by the loss of active mental connections of the subject with the world around him. Sleep is vital for higher animals and humans. For a long time it was believed that sleep is a rest necessary to restore the energy of brain cells after active wakefulness. However, it turns out that brain activity during sleep is often higher than during wakefulness. It was found that the activity of neurons in a number of brain structures increases significantly during sleep, that is, sleep is an active physiological process.
Reflex reactions during sleep are reduced. A sleeping person does not react to many external influences unless they are excessively strong. Sleep is characterized by phase changes in IRR, which are especially clearly manifested during the transition from wakefulness to sleep (equalizing, paradoxical, ultraparadoxical and narcotic phases). During the narcotic phase, animals stop responding with a conditioned reflex reaction to any conditioned stimuli. Sleep is accompanied by a number of characteristic changes in vegetative parameters and bioelectrical activity of the brain.
The state of wakefulness is characterized by low-amplitude, high-frequency EEG activity (beta rhythm). When the eyes are closed, this activity is replaced by the alpha rhythm, and the person falls asleep. During this period, awakening occurs quite easily. After some time, “spindles” begin to appear. After about 30 minutes, the “spindle” stage is replaced by the stage of high-amplitude slow theta waves. Awakening at this stage is difficult; it is accompanied by a number of changes in vegetative parameters: heart rate decreases, blood pressure decreases, body temperature, etc.
The stage of theta waves is replaced by the stage of high-amplitude ultra-slow delta waves. Delta sleep is a period of deep sleep. Heart rate, blood pressure, and body temperature reach minimum values during this phase. The slow wave stage of sleep lasts 1–1.5 hours and is replaced by the appearance on the EEG of low-amplitude, high-frequency activity characteristic of the waking state (beta rhythm), which is called paradoxical, or fast wave, sleep. Thus, the entire period of sleep is divided into two states, which replace each other 6–7 times during the night: slow wave (orthodox) sleep and fast wave (paradoxical) sleep. If you wake up a person during the phase of paradoxical sleep, he reports dreams. A person waking up in the slow-wave sleep phase usually does not remember dreams. If a person is selectively deprived of only the paradoxical phase of sleep during sleep, for example, by waking him up as soon as he enters this phase, then this leads to significant disturbances in mental activity.
Literature
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