Neuroscience

The dreaming brain tunes out the outside world

Scientists from the CNRS and the ENS-PSL in France and Monash University in Australia have shown that the brain suppresses information from the outside world, such as the sound of a conversation, during the sleep phase linked ...

Psychology & Psychiatry

Rare sleep disorder common among veterans with PTSD

Military veterans with post-traumatic stress disorder or concussion suffer from a thrashing form of sleep behavior at a rate that is far higher than the general population, according to a new study by researchers at the VA ...

Neuroscience

Key to learning and forgetting identified in sleeping brain

Distinct patterns of electrical activity in the sleeping brain may influence whether we remember or forget what we learned the previous day, according to a new study by UC San Francisco researchers. The scientists were able ...

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Rapid eye movement sleep

Rapid eye movement (REM) sleep is a normal stage of sleep characterized by rapid movements of the eyes. REM sleep is classified into two categories: tonic and phasic. It was identified and defined by Kleitman and Aserinsky in the early 1950s.

Criteria for REM sleep includes not only rapid eye movements, but also low muscle tone and a rapid, low voltage EEG -- these features are easily discernible in a polysomnogram, the sleep study typically done for patients with suspected sleep disorders.

REM sleep in adult humans typically occupies 20-25% of total sleep, about 90-120 minutes of a night's sleep. During a normal night of sleep, humans usually experience about 4 or 5 periods of REM sleep; they are quite short at the beginning of the night and longer toward the end. Many animals and some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM. The relative amount of REM sleep varies considerably with age. A newborn baby spends more than 80% of total sleep time in REM. During REM, the activity of the brain's neurons is quite similar to that during waking hours; for this reason, the sleep stage may be called paradoxical sleep. This means that there are no dominating brain waves during REM sleep.

REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as non-REM sleep (NREM). Vividly recalled dreams mostly occur during REM sleep.

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