Distribution of REM latency in depression.

While shortened REM latency is now considered the most consistent sleep feature observed among patients suffering from primary depressive episodes, and one which has generated a variety of hypotheses regarding possible mechanisms, few studies have employed long-term longitudinal designs. In the present investigation, REM latency was examined in 22 hospitalized depressed patients who were studied nightly during a 5-week protocol were bimodally distributed medication during that period; REM latencies were bimodally distributed with peaks occurring shortly after sleep onset and again 30-40 min later. Very short REM latencies (less than or equal to 20 min) were neither uncommon nor isolated events and persisted over time in this patient sample. These findings are discussed in relation to findings on shortened REM latency in other study populations.