Minute-by-minute analysis of REM sleep timing in major depression

Sleep changes described in depressed patients may represent alterations in the timing of rapid-eye-movement (REM) sleep or sleep onset. We examined these variables in groups of healthy control subjects (n = 47), depressed outpatients (n = 98), and depressed inpatients (n = 41). Outpatient depressives had greater severity of clinical symptoms than inpatients using the Hamilton Rating Scale for Depression. The depressed inpatient group had a later mean sleep onset time than the other groups, and the depressed outpatient group had a wider range of good night times than control subjects. REM timing in each group was examined as a relative frequency distribution of REM sleep (FDRS) for each minute across the night. The FDRSs for the three groups were statistically compared using the parameters from a two-component model, which includes a deterministic sinusoidal function and a time series process for errors. The slope of the linear trend in the FDRS rhythm was smaller (less positive) for both depressed groups than for controls. The ultradian FDRS rhythm occurred at an earlier phase, relative to sleep onset, in the inpatient depressed group compared to the control group. The ultradian FDRS rhythm had a longer period in the outpatient group compared to the control and inpatient groups. When referenced to 24-hr clock time in an exploratory analysis, the depressed groups appeared to have less robust FDRS ultradian rhythms than controls, but they did not appear to have a systematic phase alteration compared to controls. Abnormalities of REM sleep timing in groups of depressed patients may reflect a disturbance of sleep initiation and generation, or difficulty in entrainment of REM, rather than a systematic phase alteration in REM sleep propensity.