REM sleep

Periods of sleep in which both eyes move together in rapid jerks. Eugene Aserinsky and Nathaniel Kleitman reported them in 1953; sleepers woken during them usually described detailed dreams.

At the University of Chicago, Aserinsky switched from a task on blinking at the onset of sleep to recording lid and eye movements all night^[2]. In twenty healthy adults he found periods when both eyes moved together in rapid jerks. In eleven people left to sleep undisturbed, the first period began on average 3 hours 14 minutes after going to bed and lasted about 20 minutes, and a second began on average 2 hours 16 minutes after the start of the first. The EEG during these periods was low and irregular, and breathing quickened from an average of 13.4 to 16.9 breaths a minute^[1].

Of 27 awakenings during the eye movements, 20 produced detailed dreams. Of 23 awakenings while the eyes were still, 19 produced no recall at all. The paper concluded that the method gave a way to count how often, and for how long, people dream^[1].

At a scientific meeting that same year Aserinsky introduced the acronym REM. By his own account, the finding contradicted the view, held by Pavlov and by Kleitman himself, that the cortex rests during sleep^[2].