Reduced rapid-eye-movement (REM) sleep latency and increased REM sleep activity are associated not only with increased risk of recurrent depressive episodes but also with shortened time to the onset of subsequent episodes. Increased REM sleep activity might be a sign of attempt to excite the photic-responsive brain regions during the night, and there is a negative correlation between regional blood flow in the dorsolateral prefrontal cortex and REM sleep. The relative deactivation of the dorsolateral prefrontal cortex as a result of a developmental abnormality could explain the increased REM sleep activity during the first half of the night and the subsequent terminal insomnia among depressed subjects.