Traditional sleep stage scoring (1) has provided an effective means to summarize nightly sleep. However, traditional sleep stage scoring has been less sensitive to the relationship between brief events and the sleep process. As sleep deprivation has improved the understanding of the role of total sleep time in preserving alertness and function, sleep fragmentation has allowed the description and examination of the microstructure of sleep and the relationship of such brief events to sleep restoration. Sleep fragmentation is the result of these increases in electroencephalographic frequency, called arousals, that are frequently associated with extrinsic or intrinsic events (e.g., noise or apnea) but which may not be scored using the traditional Rechtschaffen and Kales rules (1). A working definition of electroencephalographic arousals has been published as an American Sleep Disorders Association (ASDA) report (2), although research continues to refine the parameters of arousal events. Most studies have defined an electroencephalographic arousal as “an abrupt shift in electroencephalographic frequency, which may include theta, alpha and/or frequencies greater than 16 Hz but not
Supported by the Dayton Department of Veterans Affairs Medical Center, Wright State University School of Medicine, and the Sleep-Wake Disorders Research Institute
spindles” with several additional criteria. The most contentious of the additional criteria proposed by the ASDA report was that the electroencephalographic frequency shift be at least 3 sec in duration.