Sleep disturbance in depression reconsidered.

The well documented observation of a characteristic sleep disturbance in depression has been accorded a good deal of significance. Several current hypotheses regarding the etiology of depression, are based on these findings. However, a review of the descriptive studies shows that care has not generally been taken either to restrict or objectively measure daytime sleep. Evidence is presented suggesting that daytime sleep may occur in depressed patients more frequently than commonly thought and that, in normal subjects, daytime napping can result in nocturnal sleep changes similar to those seen in depressed patients. A model is proposed in which the nocturnal sleep disturbance in depression reflects the occurrence, during the daytime, of frank slow wave sleep or periods of large amplitude, slow wave EEG activity as a consequence of a dampening of the circadian rhythm of sleep propensity.