The temporal onset of individual symptoms in winter depression: differentiating underlying mechanisms.

The transition from well to depressed offers a window to the mechanisms which underlie depressive symptoms. We examined the onset of each of 15 symptoms in 53 patients with winter depression. Three symptoms had a risk of onset closely associated with the onset of the episode itself and may represent a core syndrome. The risk of onset for the remaining symptoms was unrelated to the onset and the course of the episode. The symptoms were equally likely to begin at any time during the episode and suggest a different pathological mechanism. A dual vulnerability hypothesis is proposed; research and treatment implications are discussed.