What Rest in Flies Can Tell Us about Sleep in Mammals

periods of immobility during which only sporadic extensions and retractions of the proboscis and twitches of the abdomen also occurred could last as long as 157 min. The majority of these bouts of immobility were Ͼ30 min. In contrast, periods of immobility that lasted Ͻ1 Menlo Park, California 94025 Department of Biological Sciences min were unusual, averaging only 16.6 min per 24 hr, and therefore were distinguished as " pauses in activity " in contrast to " rest " periods. Based on these criteria, the major " rest " period in Drosophila was found to average about 7.5 hr per day and was typically terminated by a burst of activity (Hendricks et al., 2000). Sleep is widely acknowledged to have a restorative func-Observations of flies in both group and isolated envi-tion. Whereas considerable progress has been made in ronments demonstrated that decreased responsiveness understanding the brain regions that contribute to sleep to sensory stimuli accompany these periods of extended onset, the cellular bases of the cortical activity detect-immobility (Hendricks et al., 2000; Shaw et al., 2000). able in the electroencephalogram (EEG) used to define Resting flies generally ignored contacts from active flies, different stages of sleep, and the cyclicity between rapid whereas active flies react to such contacts by increasing eye movement (REM) and non-REM (NREM) sleep, iden-locomotion and sometimes engaging in courtship be-tification of what exactly is restored during sleep that havior. Both manual and automated procedures demon-is beneficial to an organism remains obscure. Given the strated that the response threshold to stimulation was widespread occurrence of " sleep-like " behavior among elevated in resting flies relative to active flies. the vertebrates and in the few invertebrates studied to Rest periods were homeostatically regulated in Dro-date, the suspicion has been that sleep as observed in sophila. Flies deprived of rest for 12 hr during the normal mammals is based on a common need for restoration rest period by either manual or automated means exhib-that is ubiquitous in the animal kingdom. Two recent papers (Hendricks et al., 2000; Shaw et al., 2000) suggest ited 3-to 7-fold more rest during the subsequent active that a genetic model in flies may help elucidate both period (Shaw et al., 2000). In contrast, flies stimulated the genetic control of sleep and the restorative process for 12 hr during the normal active period showed no that occurs during sleep. increase in rest during the subsequent …