C. Thompson et al., EFFECTS OF MORNING PHOTOTHERAPY ON CIRCADIAN MARKERS IN SEASONAL AFFECTIVE-DISORDER, British Journal of Psychiatry, 170, 1997, pp. 431-435
Background The suppression of melatonin by light at 00.30 hours has be
en shown to be greater in winter than in summer in patients with seaso
nal affective disorder (SAD) but not in matched normal controls. Metho
d In this study 12 patients with SAD and 12 matched normal controls we
re exposed to morning light therapy in the winter. Melatonin profiles
and sensitivity to light were measured before and after treatment. Res
ults The SAD but not the normal group showed a phase advance of melato
nin rhythms in response to phototherapy. There was an association betw
een phase position and phase shift in the SAD but not in the normal gr
oup. Conclusions There may be instability of circadian rhythms in SAD
mediated by a high-amplitude phase response curve, rather thana fixed
phase abnormality as had been previously suggested. This instability m
ay be secondary to impaired serotoninergic function in the afferent pa
thways to the suprachiasmatic nuclei.