Delta sleep ratio as a predictor of sleep deprivation response in major depression

The fast but short-lasting improvement of depressive symptoms by sleep depr ivation (SD) in about 60% of patients with a major depressive disorder is w ell established, but the mechanisms of action are still not clear. Recent s tudies suggest that changes in non rapid eye movement (NREM) sleep, especia lly in slow wave activity (SWA), could be associated with the therapeutic o utcome of SD. In the current study, spectral analysis of NREM sleep EEG dir ectly prior to SD was performed to determine if automatically derived sleep parameters predict SD response. Sixteen pair matched and drug free patient s with a major depressive disorder, 8 SD responders and 8 non-responders (r esponse criterion: 50% reduction on the 6-item HAMD score), were included. Average EEG spectral power was calculated for the whole night before SD and for single NREM episodes. While whole-night averages of spectral power did not differ significantly between subgroups, SD responders showed a steady decrease of SWA across successive NREM episodes, whereas in non-responders an increase from the first to the second episode was observed. The differen t distribution of SWA was significantly expressed in the delta sleep ratio (quotient of SWA in the first to the second NREM episode). In conclusion, a high delta sleep ratio is a positive predictor for SD response. Referred t o psycho- and pharmacotherapeutic results it is hypothesized that low and h igh values of the delta sleep ratio characterize subgroups of depressed pat ients with different neurobiological alterations, which could be relevant f or further scientific and therapeutic approaches. (C) 2001 Elsevier Science Ltd. All rights reserved.