Background. Recent studies have suggested that major depressive disorders are associated with a breakdown in the organization of ultradian rhythm in sleep EEG. The present study used cross-spectral analysis of sleep EEG to confirm this finding, in a larger-scale study, evaluating the influence of gender and age on ultradian rhythms in depression.

Methods. Temporal coherence of ultradian (80–120 min) rhythms in beta, theta and delta, recorded from central and parietal sites, were compared in 120 symptomatic, unmedicated, depressed out-patients and 59 healthy normal controls.

Results. Few macro-architectural differences were noted between patients and controls. However, interhemispheric beta and theta coherence and intrahemispheric coherence between beta and delta rhythms were significantly lower in depressed patients. Coherence measures were lowest in women with depression and highest in men in the control group, but were not strongly influenced by age. Over 65% of depressed patients were [ges ]2 standard deviations below normal on at least one coherence measure, in sharp contrast to less than 10% of patients on macro-architectural variables.

Conclusions. It was concluded that dysregulation of ultradian rhythms characterizes the majority of depressed out-patients, primarily women, even when macro-architecture did not differentiate groups. The outcome of this study supports the view that the pathophysiology of depression is strongly influenced by gender. It was suggested that low temporal coherence in depression reflects a breakdown in the organization of sleep EEG rhythms within and between the two hemispheres.