Rapid eye movement sleep in the brains of sleeping cats. In 1944, Ohlmeyer reported 90-minute ultradian sleep cycles involving male erections lasting for 25 minutes. At University of Chicago in 1952, Eugene Aserinsky, Nathaniel Kleitman, and William C. Dement, discovered phases of rapid eye movement during sleep, and connected these to dreaming. Their article was published September 10, 1953. Aserinsky, then Kleitman, first observed the eye movements and accompanying neuroelectrical activity in their own children. William Dement advanced the study of REM deprivation, with experiments in which subjects were awoken every time their EEG indicated the beginning of REM sleep. He published "The Effect
Rapid eye movement sleep tomography, and reports of dreamers upon waking, have all been used to study this phase of sleep. 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. Electroencephalography during REM deep sleep reveal 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. An important element of this contrast is the θ (theta) rhythm in the hippocampus that show 40–60 Hz