Distribution of REM latencies after sleep interruption in depressive patients and control subjects

The REM sleep latency of 16 endogenous depressives and 10 normal controls was obtained over a series of nights, once at evening onset of sleep and once after a deliberate sleep interruption at 2:30 AM. Twelve of the patients were studied again during a follow-up some months later, when they were free of depressive symptoms. The patients were classified into Group A (n = 9) if they displayed sleep onset REM episodes (SOREMs) at evening sleep onset, or Group B if they did not have SOREMs at evening sleep onset. Group A patients had significantly more SOREMs after the deliberate sleep interruption than Group B patients, during depression as well as in the symptom-free interval. REM latency appears to depend on several different factors: (a) the predisposition of the person, (b) the time of day, and (c) REM pressure, which seems to increase within a REM-REM interval.