On the explanation of short REM latencies in depression.

Sleep in depression is characterized by the occurrence of episodes of rapid eye movement (REM) sleep at sleep onset. The empirical foundations of three hypotheses about the origin of this phenomenon are examined: A circadian rhythm hypothesis stating that sleep onset REM episodes (SOREMs) are the result of an abnormal phase-position of the REM sleep production cycle. A REM sleep-slow wave sleep interaction hypothesis that attributes SOREMs to a low non-REM sleep propensity. A circadian amplitude hypothesis, in which a flattening of the circadian arousal cycle is thought to be causally related to SOREMs. None of the hypotheses are found to be supported by firm empirical evidence.