Sleep deprivation is a potentially powerful strategy for discovering the function(s) of sleep, but the approach has had limited success. Few studies have described serious physiological consequences of sleep deprivation, perhaps because the deprivation has not been maintained long enough. However, prolonging deprivation usually requires sustained, frequently intense stimulation, which makes it difficult to determine whether subsequent impairment resulted from the sleep loss or from the stimulation per se. Accordingly, several older studies that showed severe impairment have been neglected or discounted, because the impairment could have resulted from the stimulation. To evaluate the effects of sleep deprivation independent of the stimulation used to enforce deprivation, we have used an apparatus that can awaken experimental rats while delivering the same gentle stimulation to control rats according to a schedule that only moderately shortens their sleep.