The role of activation in the effect of total sleep deprivation on depressed mood.

The present investigation analyzes if the effect of Total Sleep Deprivation (TSD) on depressive mood in normal subjects is related to participants' activation levels. Reaction time (RT), subjective sleepiness, and depressive mood were assessed among 48 normal subjects who were subjected to 60 h of TSD. Subjects were divided into groups based on his/her depressive mood changes following TSD: subjects with worse response (n = 11), subjects with better response (n = 12), and intermediate group (n = 25). We sought to determine if RT and subjective sleepiness were related systematically to depressive mood changes following TSD. TSD produces a general reduction in activation (i.e., a monotonic increase in RT and subjective sleepiness) modulated by circadian oscillations. Baseline activation (RT) was confirmed partially as a predictor of participants' response to TSD. Subjects with high levels of activation (lower RTs at the baseline) experienced a better response (greater reductions in depressive mood) following TSD. There was no relationship between pre-treatment subjective sleepiness levels and the TSD effect on depressive mood. The results partially support the role of the activation level as a differential moderator of TSD effects on depressive mood in normal subjects.