Temporal characteristics of delta activity during NREM sleep in depressed outpatients and healthy adults: Group and sex effects

Study Objectives: The primary aim was to evaluate group and sex differences in delta activity across non-rapid eye movement (NREM) sleep in depressed patients and healthy controls. Design: Repeated-measures ANOVA contrasted delta power, amplitude and incidence in the first three NREM periods (stages 2, 3, and 4) of sleep. The time course of delta activity was evaluated with exponential regressions. Age effects on delta were evaluated with linear regression analysis. Setting: Two consecutive nights were spent in the laboratory, the first of which served as adaptation. Patients or Participants: Twenty-two (9 men, 13 women) symptomatic, but unmedicated, outpatients with major depressive disorder (MDD) and 23 healthy controls (15 men, 8 women) participated in the study. Measurements and Results: Delta power and amplitude showed significant group by sex interactions. Men with MDD showed lower power and amplitude in NREM sleep compared to women with MDD, but did not differ significantly from controls. However, the time course of delta power and amplitude was significantly different in men with MDD, with lower accumulation and slower dissipation across NREM sleep than all other groups. Women with MDD showed no evidence of lower delta power and amplitude or an abnormal time course compared to control women or men. Age had a differential influence on delta activity between the groups, with little age-related change in delta activity in the depressed groups. Conclusions: It was concluded that slow-wave sleep deficiencies may be characteristic of men, but not women, with MDD. It was also concluded that the influence of age on delta activity varied as a function of both psychiatric status and sex.