The cortical and thalamic neurons in the waking and REM sleeping brain are more depolarized (fire more readily) than in the NREM deep sleeping brain. 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 patterns of EEG activity similar to these rhythms are also observed during wakefulness. Electroencephalography during REM deep sleep reveals fast, low amplitude, desynchronized neural oscillation (brainwaves) that resemble the pattern seen during wakefulness, which differ from the slow δ (delta) waves pattern of NREM deep sleep. Although the body is paralyzed, the brain acts as if it is somewhat awake, with cerebral neurons firing with the same overall intensity as in wakefulness. REM sleep is called "paradoxical" because of its similarities to wakefulness. Physiology Electrical activity in the brain Polysomnographic record of REM Sleep. Techniques of neurosurgery, chemical injection, electroencephalography, positron emission tomography, and reports of dreamers upon waking, have all been used to study this phase of sleep.
Subjects allowed to sleep normally again usually experience a modest REM rebound. Many experiments have involved awakening test subjects whenever they begin to enter the REM phase, thereby producing a state known as REM deprivation. REM sleep was further described by researchers, including William Dement and Michel Jouvet. In 1953, Professor Nathaniel Kleitman and his student Eugene Aserinsky defined rapid eye movement and linked it to dreams.
The body abruptly loses muscle tone, a state known as REM atonia. Organisms in REM sleep suspend central homeostasis, allowing large fluctuations in respiration, thermoregulation and circulation which do not occur in any other modes of sleeping or waking. REM sleep occurs 4 times in a 7 hour sleep. The transition to REM sleep brings marked physical changes, beginning with electrical bursts called "ponto-geniculo-occipital waves" ( PGO waves) originating in the brain stem. As sleep cycles continue, they shift towards a higher proportion of REM sleep. REM and non-REM sleep alternate within one sleep cycle, which lasts about 90 minutes in adult humans. The absence of visual and auditory stimulation ( sensory deprivation) during REM sleep can cause hallucinations.
REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as non-REM sleep (NREM sleep, NREMS, synchronized sleep). Experiences of REM sleep are not transferred to permanent memory due to absence of norepinephrine. Electrical and chemical activity regulating this phase seems to originate in the brain stem, and is characterized most notably by an abundance of the neurotransmitter acetylcholine, combined with a nearly complete absence of monoamine neurotransmitters histamine, serotonin and norepinephrine. The REM phase is also known as paradoxical sleep ( PS) and sometimes desynchronized sleep or dreamy sleep, because of physiological similarities to waking states including rapid, low-voltage desynchronized brain waves. Rapid eye movement sleep ( REM sleep or REMS) is a unique phase of sleep in humans, mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. EEG of a mouse that shows REM sleep being characterized by prominent theta-rhythm Phase of sleep characterized by random & rapid eye movements A sample hypnogram (electroencephalogram of sleep) showing sleep cycles characterized by increasing paradoxical (REM) sleep.
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