REM sleep in depressed patients: different attempts to achieve adaptation.

Twenty-seven depressed patients and 10 healthy subjects were investigated in the sleep laboratory during two to three consecutive nights. Eleven of the 27 patients demonstrated the "first night effect" (group I) and 11 other patients demonstrated a clear absence of the "first night effect" (group II). Five of the 27 depressed patients were omitted from the study because they did not fit criteria for first night effect. The 10 healthy controls demonstrated a first night effect. In group I, the duration of the first rapid eye movement (REM) sleep episode was increased on the first night and on the second night the REM sleep latency was decreased, whereas REM sleep duration and eye movement (EM) density was increased. The number of the short sleep cycles (less than 40 minutes) was greater in group I versus group II and the percentage of slow-wave sleep (SWS) was also higher in group I. In depressed patients with the "first night effect" the enhanced REM sleep requirement is satisfied not only by an increased REM sleep duration but also by the improved REM sleep quality that is crucial for adaptation. The adaptive role of the increased first REM period and the increased EM density in this period is very limited.