Biological rhythm disturbance in depression: temporal coherence of ultradian sleep EEG rhythms

Background. Recent studies have suggested that major depressive disorders a re associated with a breakdown in the organization of ultradian rhythm in s leep EEG. The present study used cross-spectral analysis of sleep EEG to co nfirm this finding, in a larger-scale study, evaluating the influence of ge nder and age on ultradian rhythms in depression. Methods. Temporal coherence of ultradian (80-120 min) rhythms in beta, thet a and delta, recorded from central and parietal sites, were compared in 120 symptomatic, unmedicated, depressed outpatients and 59 healthy normal cont rols. Results. Few macro-architectural differences were noted between patients an d controls. However, interhemispheric beta and theta coherence and intrahem ispheric coherence between beta and delta rhythms were significantly lower in depressed patients. Coherence measures were lowest in women with depress ion and highest in men in the control group, but were not strongly influenc ed by age. Over 65 % of depressed patients were greater than or equal to 2 standard deviations below normal on at least one coherence measure, in shar p contrast to less than 10 % of patients on macro-architectural variables. Conclusions. It was concluded that dysregulation of ultradian rhythems char acterizes the majority of depressed out-patients, primarily women, even whe n macro-architecture did not differentiate groups. The outcome of this stud y supports the view that the pathophysiology of depression is strongly infl uenced by gender. It was suggested that low temporal coherence in depressio n reflects a breakdown in the organization of sleep EEG rhythms within and between the two hemispheres.