TOTAL SLEEP-DEPRIVATION IN THE RAT TRANSIENTLY ABOLISHES THE DELTA AMPLITUDE RESPONSE TO DARKNESS - IMPLICATIONS FOR THE MECHANISM OF THE NEGATIVE DELTA REBOUND

1. The homeostatic model of delta sleep has provided a useful framework for basic sleep research. This model is based on the relation of delta EEG to the duration of prior waking in man, a relation highlighted by the marked increase (rebound) in the delta EEG of nonrapid eye movement (NREM) sleep that follows total sleep deprivation (TSD). The generality of this model is severely challenged by the response to TSD in the rat. In the 12-h light period (LP) that immediately follows TSD, the rat shows a massive increase in REM sleep but only a modest increase in NREM delta EEG. Although this initial delta increase does not nearly compensate for the delta lost during deprivation, the rat then exhibits a depressed rate of delta production (the ''negative delta rebound''). This robust and reproducible reaction worsens the delta deficit. 2. Using rats with chronic electrode implantations, we deprived them of all sleep for 24 h by handling them gently when they became inactive. We found that the negative delta rebound entails a transient, near-total failure of delta amplitude to increase normally in response to the onset of darkness. This loss of the rat's EEG response to darkness suggests a disruption of basic sleep physiology and raises the possibility that the negative rebound is also a pathological response. 3. We hypothesize that the negative rebound is maladaptive, and is caused by the massive increase in REM sleep that precedes it; this hypothesis can be tested experimentally. We also note that the negative delta rebound could provide a useful tool for investigating the functional significance and the neurophysiological mechanisms of NREM delta EEG. 4. Our results with gentle handling confirm the finding that this method of TSD produces a far smaller initial delta increase than that reported for TSD with forced locomotion. This difference indicates that a factor besides simple sleep loss contributes to the EEG response to sleep deprivation by forced locomotion.