Abstract
To the Editor.— The discovery of the antidepressive effects of light 1 in seasonal affective disorder, winter type, 2 has inspired explanations of pathogenesis of and therapy for this disorder in terms of circadian (dys)regulations. The original hypothesis of day length being the crucial variable was rapidly rejected. 3 Subsequently, circadian phase 4 and the daily total number of photons received by the patient 3 were proposed as relevant factors. Unfortunately, neither of these proposals appeared to be compatible with all experimental data. In the present study, aspects of the previous hypotheses are put together into a new hypothesis, the outlines of which will be discussed. The Circadian Pacemaker.— Functions of the circadian pacemaker are twofold. Apart from regulating the timing of processes within the circadian range, the pacemaker controls the annual timing of certain behaviors. To survive, many species must migrate, molt, hoard food, hibernate, and reproduce at
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