Sleep

Phases of sleep

At individuals, at the time one night, three to five cycles of 90 minutes sleep can be followed, which are composed of five distinct phases. The first four phases correspond to the Sleep with Slow Waves (GROUND), the electrical measurements being very weak.

Description

The data of the EEG during the day before and the sleep are like those of the animal. They are however more complex than in the animal. These data make it possible to distinguish various stages in the sleep.

• Somnolence

It acts of the stage 1 which is the stage of drowsiness (stage of transition between the awakening and the sleep). It is characterized by a reduction of vigilance, muscular tone and heart rate. The muscular movements are slow (the ocular spheres " roulent"). The latency of drowsiness regarded as normal is lower than twenty minutes. Beyond, it is about a Insomnie. Notable fact, the phase of drowsiness is never perceived, contrary to the alarm clock of this one (example of drowsiness at the time of driving of a car). The Hypnagogie often has place during phase I, but not toujours.

Onde Théta: 3.5 to 7.5 Hz

• light Sleep

the light sleep (or stage 2) occupies approximately 50% of the time of total sleep. The subject is dormant, but it is still very sensitive to the external stimuli. Thus in stage 2,50% of the good sleepers and 80% of the bad sleepers think not dormir.

Onde Théta: 3.5 to 7.5 Hz and complex K (spindles or spindles, 12 to 14 Hz)

• Deep sleep

the deep sleep corresponds to phases 3 and 4: the electric activity consists of slow waves, the waves delta (< 3.5 Hz), and the vital signs slow down while becoming regular. At the stage 3 a very discrete muscular activity persists and the ocular movements almost disappeared. It is at the stage 4 that can sometimes occur the night terrors or the Somnambulisme.

It is at this time that the cellular divisions and the production of the Growth hormone take place, from where importance of the sleep at the Enfant. The deep sleep occupies approximately 100 minutes, whether the person is a small sleeper or a large sleeper. It tends to decrease with the age, with the profit of stage 2.

For anecdote, Celia Green brings back an experiment where an Indian Master called Swami Rama started to produce waves delta consciously, five minutes after being entered in Méditation, and having been able to tell, after these 25 minutes of meditation, which had occurred around him during the recordings.

• paradoxical Sleep

See also: paradoxical Sleep

Contrary to the other phases, the electric activity of the Brain, the eyes is very important at the time of the paradoxical sleep, whereas there exists a quasi total muscular lifelessness, apart from the ocular movements which occur by jerks. The néocorticale activity is closer to that of the awakening than that of the slow sleep. Breathing is irregular. The heart accelerates or slows down. One observes a dilation of the pelvic bodies and an erection which can be followed by ejaculation. This phase is repeated every 90 minutes, and its duration lengthens with the succession of the cycles of the sleep, to become maximum at the end of the night. It is the period favourable with the dreams (but also with the Cauchemar S), although the dreams can occur during the sleep lent.

the paradoxical sleep corresponds approximately to 20 25% of the total time of sleep.

The polygraphic recordings (EEG, EMG and EOG) made it possible to make the connection between the dream and the paradoxical sleep. Studies were ridges on several individuals at various stages of the sleep. They showed that when one awakes these individuals during various stages of their sleep, the quality of the memory of their dream is function of the stage to which they are awaked.

Indeed, the subjects awaked during their paradoxical sleep remember with much more details of their dream, while if one awakes them during the slow sleep, they souviennet in a very fuzzy way or they do not preserve any memory of their dream.

The study also showed that the importance of the movement occulaire, the increase in the cardiac rhythm and the intensity of the dream are correlated. These studies concluded that 80% of the dreams occur during the paradoxical sleep. However, the oneiric activities can also take place during certain stages of the slow sleep. Thus should not be superimposed the " terms; rêve" and " sleep paradoxal".

The hypnogramme

During one night of sleep, the periods of paradoxical sleep lengthen more and more. On the contrary, the phases of major slow sleep (stages 3 and 4) are shortened and disappeared, with the profit of stage 2. The hypnogramme makes it possible to visualize these different stades.
At the end of each cycle, there exists, in a completely normal way, the briefs alarm clocks which the person does not remember the morning. However certain people remember only these awakenings and believe wrongly that they did not close the eye of the nuit.
When occur of the unexpected alarm clocks, the subject must pass by again in sleep 1, then 2 then 3 and 4. Thus, the people suffering from Apnée of the sleep hardly exceed stage 2 because of the frequent alarm clocks induced by the Hypoxie. The sleep is thus of bad quality, person in charge of diurnal access of somnolence.

Functional states of the brain

Conscience during the sleep

The sleep is made up various phases of conscience. Those are not uniform. They are not either obligatorily present during one night of sleep, far from there (and fortunately). This list recapitulates these various forms of conscience.

; The Dream: In the past, it was thought that the dream exclusively took place during the phase of paradoxical sleep, or REM, because when one awoke the subjects during this phase, they much more often remembered their dream. In fact, the probability of obtaining a memory of dream is about 80% if the alarm clock takes place during phase REM, and of 20% apart from this phase. This calls into question the fact that the dreams exclusively take place during the phase of paradoxical sleep. ; Hypnagogic and hypnopompic hallucinations: They respectively take place during the phase of drowsiness and the phase of alarm clock. They are in fact auditive or sound experiments rather fugacious and which do not have the development of the dreams. ; A thinking activity: It would be held rather during the phases of sleep not REM. This activity is of nature little or not sensory. Not very elaborate compared to that the discovery, it is more repetitive. ; The Paralysis of the sleep: Very distressing, it appears by a paralysis of the body (physiological during the phase of paradoxical sleep) whereas the subject is awaking. In spite of intense efforts, the subject does not manage to move during a certain time, which can start attacks of panic. Certain people think that it is acted in fact of a “false alarm clock” during a dream, the dreamer “hallucinating” to some extent his alarm clock, possibly announcing a lucid dream. ; The night terrors: It is about a parasomnie of the slow sleep (near to the sleepwalking) frequent in the child before 8 years and who appears by a brutal dissociated alarm clock accompanied by cries of panic. The child is still in half sleep and if it completely is awaked, it is unable to give explanations. The amnesia of the incident is of rule in the morning. ; The lucid Dream: The dreamer is aware that he dreams in his dream. They are dreams whose clearness of the dreamer is very accentuated, as well as a strong sensoriality.

Pathologies of the sleep

Some figures

• excessive diurnal somnolence reaches 8% of the population, 20 to 30% of the population suffers from not very severe insomnia, 5 to 15% of the population suffers from severe insomnia, 15 to 20% of the adults occasionally use sleeping pills, 10% have a regular use of it.
• the professional consequences of insomnia are an increase in the sick leave (31% versus 19% in the good sleepers) and in the industrial accidents (8% versus 1%). At least 8% of insomnia are of professional origin.
• 20% of the road accidents in the industrialized countries is ascribable to drowsiness at the wheel: by deprivation of sleep, by excessive diurnal somnolence or drugs.
• diurnal somnolence and the hypersomnies are less well-known. At the 30-60 years, 9% of the men suffer from the syndrome of apnea of the sleep, against 4% among women.

Classification

The sleep disorders are divided into two categories: the parasomnies which are demonstrations which accompany the sleep, being able to disturb it or not, and the dyssomnies which consist of a deterioration of the quantity or quality of the sleep.

See also: Parasomnie, Dyssomnie, international Classification of the sleep disorders