Sleep and circadian rhythms in mood disorders

Objective: Self-reported sleep disturbances are present in over 80% of patients with depression. However, sleep electroencephalography (EEG) findings, based on overnight polysomnography have not always differentiated depressed patients from healthy individuals. Method: The present paper will review the findings on sleep EEG studies in depression highlighting how recent technological and methodological advances have impacted on study outcomes. Results: The majority of studies, including our own work, do indicate that sleep homeostasis and sleep EEG rhythms are abnormal in depression, but the sleep disturbances were strongly moderated by gender and age. Melancholic features of depression correlated significantly with low slow-wave activity in depressed men, but not in depressed women. Women with depression showed low temporal coherence of sleep EEG rhythms but the presence or absence of melancholic features did not influence correlations. Conclusion: Diagnostic classification schemas and clinical features of depression may influence sleep EEG findings, but gender may be a more important consideration.