PHASE TYPING OF PATIENTS WITH SEASONAL AFFECTIVE-DISORDER - A TEST FOR THE PHASE-SHIFT HYPOTHESIS

The study evaluates the phase-shift hypothesis for seasonal affective disorder (Lewy et al., 1987, 1988) in parallel-design comparison of ef fects of morning (800-1000) or afternoon (1600-1800) light treatment o n mood and circadian phase. Subjective arousal, body temperature, mela tonin and cortisol were measured at 800, 1200, 1600, 2000 and 2400 in 23 women with seasonal depression and 20 controls before and after a w eek of bright light (2 hours per day). The rates of clinical response to both treatments were similar. Comparison of circadian variations di d not provide evidence for significant phase-delay in patients compare d to controls. However, morning light produced significant phase advan ce in patients, but not in controls. Also we found that advance phase shifts in well-responded patients were more often than in patients wit h worse response and controls. Before light treatment phase concordanc e between different variables in patients was lower compared to either themselves after light treatment or controls before and after light t reatment. Dependence of antidepressant response to light from pretreat ment circadian phases was also observed. Those patients who responded worse to morning light tended to have advance circadian phases, while those who responded worse to afternoon light tended to have delay phas es. Although some results are lending support for the phase-shift hypo thesis, other explanations for mechanisms by which biological rhythms are implicated in winter depression and light treatment might be sugge sted.