[Season-related forms of depression. II. Modification by phototherapy and biological results].

The efficacy of phototherapy with bright, fluorescent, full-spectrum light for treatment of seasonal affective disorders (SAD) has now been widely demonstrated in controlled studies. However, treatment with dim light did not reveal a significant therapeutic improvement. Specific parameters of light treatment are necessary or optimal for producing this response and light intensity and duration in contrast to timing and spectrum seem to be a major importance. The mechanism of action of phototherapy is closely linked to the psychobiology of SAD and has not yet been satisfactorily explained. Among the several theories which have been proposed, the melatonin hypothesis and phase shift hypothesis have been the basis for the earlier studies. Newer theories also include the function of further neuroendocrine systems, as well as neurotransmitter and immune function and electrophysiological mechanisms. Until now, the value of phototherapy in the treatment of other non-seasonal syndromes has not yet been explored thoroughly and this line of research seems worth continuing.