The Sleep Research & Treatment Center (SRTC) of the Department of Psychiatry at Penn State University, College of Medicine was established at UCLA by Dr. Anthony Kales in 1963 and moved to Hershey in 1971. This sleep center is one of the few that has both a sleep disorders clinic where patients are treated as well as an active research program. Because of this dual function the SRTC is well known for defining sleep/wake characteristics of various sleep disorders [1-19].
The SRTC has also played an important role in the standardization of the currently accepted adult human sleep stage criteria. Sleep stages are divided in Rapid Eye Movement (REM) Sleep and nonREM (NREM) sleep. Sleep stage patterns are defined based upon brain wave activity (electoencephalogram [EEG], eye movements (electrooculogram [EOG]). and muscle activity (electromyogram [EMG]). The NREM sleep stages were first described in terms of EEG by Loomis, Harvey, and Hobart in 1937 . REM sleep based on eye movements and brain activity was subsequently identified by Aserinsky and Kleitman in 1954 . Dement and Kleitman revised the NREM sleep stages into four and associated dreaming with REM . Finally, loss of muscle activity during REM sleep was identified by Kales in 1964 . The need for a unified set of criteria for staging sleep was subsequently identified by Kales and in 1968 the sleep-stage scoring manual was published by Rectschaffen and Kales . This manual brought together these three variables (EEG, EOG, & EMG) in a systematic standardized manner which are the criteria used today by every sleep laboratory reporting human sleep stage data.