First night effect in depression: new data and a new approach.
Polysomnography was performed in 20 depressed patients and 8 normal controls for 2 consecutive nights. A subset of patients had 3 consecutive nights. Patients were assigned to groups according to the presence (group I) or absence (group II) of a first night effect (REM sleep latency on the first night in the laboratory was at least 30 min longer than on the second night). The groups were equivalent with regard to gender distribution, age, and severity of depression. In group I, REM sleep latency on nights 2 and 3 was significantly shorter than in group II. REM sleep percentage on the second night in group I was increased compared to the first night. A shift of REM sleep to the first cycle was prominent on the first night only in patients with a first night effect. On average, delta sleep was preserved in group I compared to group II. We suggest that the first night effect reflects a physiological system with greater capacity to respond adaptively and to preserve homeostasis when confronted with environmental stressors.