Natural Patterns Of Sleep

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DescriptionAn alternative explanation suggests that the functional purpose of REM sleep is for procedural memory processing, and the rapid eye movement is only a side effect of the brain processing the eye-related procedural memory. Neural activity during REM sleep seems to originate in the brain stem, especially the pontine tegmentum and locus coeruleus. REM sleep is punctuated and immediately preceded by PGO (ponto-geniculo-occipital) waves, bursts of electrical activity originating in the brain stem. They exhibit their highest amplitude upon moving into the visual cortex and are a cause of the "rapid eye movements" in paradoxical sleep. Other muscles may also contract under the influence of these waves. REM sleep is "paradoxical" because of its similarities to wakefulness. Although the body is paralyzed, the brain acts somewhat awake, with cerebral neurons firing with the same overall intensity as in wakefulness.
Slow-wave sleep is greatest in young children and it decreases steadily with age, even if sleep duration does not change. This may be related to changes in the structure and function of the brain. NREM sleep and REM sleep continue to alternate through the night in a cyclical fashion. Most slow-wave NREM sleep occurs in the first part of the night; REM sleep episodes, the first of which may last only one to five minutes, generally become longer through the night. During a typical night, N3 sleep occupies less time in the second cycle than the first and may disappear altogether from later cycles.
The average length of the first NREM-REM sleep cycle is between 70 and 100 minutes; the average length of the second and later cycles is about 90 to 120 minutes. The reason for such a specific cycling pattern of NREM and REM sleep across the night is unknown. The two main types of sleep are rapid-eye-movement sleep and non-rapid-eye-movement sleep.
In slow-wave sleep the eyes can drift apart; however, the eyes of the paradoxical sleeper move in tandem. These eye movements follow the ponto-geniculo-occipital waves originating in the brain stem. The eye movements themselves may relate to the sense of vision experienced in the dream, but a direct relationship remains to be clearly established. Congenitally blind people, who do not typically have visual imagery in their dreams, still move their eyes in REM sleep.
Electroencephalography during REM deep sleep reveal fast, low amplitude, desynchronized neural oscillation that resemble the pattern seen during wakefulness which differ from the slow δ waves pattern of NREM deep sleep. An important element of this contrast is the 3-10 Hz theta rhythm in the hippocampus and 40–60 Hz gamma waves in the cortex; very similar patterns of EEG activity to these rhythms are also observed during wakefulness. The cortical and thalamic neurons in the waking and REM sleeping brain are more depolarized than in the NREM deep sleeping brain. Human theta wave activity predominates during REM sleep in both the hippocampus and the cortex.
Sleepers awakened from REM tend to give longer, more narrative descriptions of the dreams they were experiencing, and to estimate the duration of their dreams as longer. Sometimes they include elements of the dreamer's recent experience taken directly from episodic memory. Most of the eye movements in "rapid eye movement" sleep are in fact less rapid than those normally exhibited by waking humans. sleep dream pillow are also shorter in duration and more likely to loop back to their starting point. About seven of such loops take place over one minute of REM sleep.
Afternoon naps for most people typically last between 30 and 60 minutes. Any longer and there is a risk of falling into deep sleep and having a difficult time waking. Following a nap, having dissipated some of the accumulated sleep drive, many people report feeling better able to stay awake and alert in the late afternoon and evening. This increased alertness typically causes people to go to bed later and generally to sleep less at night than people who do not take naps. For example, for the first year of life, sleep often begins in the REM state. The cyclical alternation of NREM-REM sleep in newborns is present from birth but at 50 to 60 minutes is much shorter than the 90-minute cycles that occur in adults. Consolidated nocturnal sleep and fully developed EEG patterns of the NREM sleep stages emerge only after two to six months.

Created26 Dec 2020
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