Comparison of overnight trends in relative power for specific frequency bands, sleep stages, and brain regions between patients with depressive disorder and matched control subjects.

Most EEG studies of MDD examined mean differences in frequency-band-specific power between MDD patients and control subjects; however, a few studies looked for differences in temporal trends in power. We focused on overnight time trends in relative power using polysomnography studies of 544 patients with MDD and 1662 age- and sex-matched controls. We sought to replicate our finding on MDD with an additional 653 patients with depressive disorder (DD) and 1959 age- and sex-matched controls. For each subject, we estimated trends as regression slopes separately for 180 features defined by six frequency bands, five sleep stages, and six brain regions. Relative theta power during stage 2 (N2) non-rapid eye movement (NREM) sleep in the frontal and central regions of the brain increased more rapidly through time in MDD patients than in controls. Similar upward trends of relative theta power were also statistically significant in DD patients. If validated in a longitudinal study, the time trend in relative theta power in the N2 stage of the NREM sleep could potentially serve as a surrogate biomarker for monitoring the responses of patients with depressive disorders to treatment.