The next article in this series celebrates the 50^th anniversary of the discovery of rapid eye movement (REM) sleep by Aserinsky and Kleitman in 1953. Eugene Aserinsky, a graduate student of the great pioneer of sleep research, Dr. Nathanial Kleitman, was interested in the study of sleep-related eye movements that had been described for many decades. Dr. Aserinsky started out this line of research combining academic and family life when he recorded the electrooculogram during sleep in his 8-year-old son in a borrowed room from the Physiology Department at the University of Chicago2. He subsequently made more sleep recordings in 20 normal adult subjects described in the report on the following page. The main discovery was that periods of "rapid, jerky eye movements" occurred cyclically across the night and were associated with low amplitude, irregular frequency electroencephalographic (EEG) activity, and changes in respiratory and heart rate. Further, dream reports obtained after awakening subjects awakened in both periods of ocular activity and inactivity demonstrated that increased dream recall was found during sleep associated with rapid eye movements. They concluded, "these physiologic phenomena, and probably dreaming, are very likely all manifestations of a particular level of cortical activity encountered normally during sleep."

The discovery of REM sleep contributed to a fundamental reconceptualization of sleep, which previously was thought to represent a passive process occurring when afferent sensory information was inadequate to maintain arousal. In contrast, the brain during REM sleep becomes metabolically and electrically activated with EEG frequencies approaching those of wakefulness. The search for the function or functions of REM sleep continues to galvanize sleep research today.