Sleep deprivation suppresses the increase of rapid eye movement density across sleep cycles

We investigated the association between rapid eye movement (REM) density (REMd) and electroencephalogram (EEG) activity during non-rapid eye movement (NREM) and REM sleep, within the re-assessment, in a large sample of normal subjects, of the reduction of oculomotor activity in REM sleep after total sleep deprivation (SD). Coherently with the hypothesis of a role of homeostatic sleep pressure in influencing REMd, a negative correlation between changes in REMd and slow-wave activity (SWA) was expected. A further aim of the study was to evaluate if the decreased REMd after SD affects ultradian changes across sleep periods. Fifty normal subjects (29 male and 21 female; mean age=24.3 ± 2.2 years) were studied for four consecutive days and nights. Sleep recordings were scheduled in the first (adaptation), second (baseline) and fourth night (recovery). After awakening from baseline sleep, a protocol of 40 h SD started at 10:00 hours. Polysomnographic measures, REMd and quantitative EEG activity during NREM and REM sleep of baseline and recovery nights were compared. We found a clear reduction of REMd in the recovery after SD, due to the lack of REMd changes across cycles. Oculomotor changes positively correlated with a decreased power in a specific range of fast sigma activity (14.75-15.25 Hz) in NREM, but not with SWA. REMd changes were also related to EEG power in the 12.75-13.00 Hz range in REM sleep. The present results confirm the oculomotor depression after SD, clarifying that it is explained by the lack of changes in REMd across sleep cycles. The depression of REMd can not simply be related to homeostatic mechanisms, as REMd changes were associated with EEG power changes in a specific range of spindle frequency activity, but not with SWA.