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While theories linking seasonality and affective episodes date back to the time of Hippocrates, it is only recently that the idea has gained widespread acceptance. The recognition that melatonin could be suppressed by bright light, the delineation of seasonal affective disorder (SAD) as a syndrome with distinct clinical and therapeutic implications, and the efficacy of bright light in the treatment of this condition, were all important steps in this regard. The therapeutic value of bright light in SAD closely aligns the biology of the disorder with its treatment and introduces into psychiatry an exciting new therapeutic modality. SEASONAL AFFECTIVE DISORDERS AND PHOTOTHERAPY brings together the latest research in four key areas: * Diagnostic profile of SAD, epidemiological issues, and specific clinical applications of light * Animal models of seasonality * Normal human seasonality and its relationship to psychiatric disorders * Biological mechanisms subserving light treatment Introductory chapters consider the different profiles of SAD and detail outcome studies across the Northern Hemisphere. Important questions are addressed about summer depression, with and without winter depression, as well as seasonality and SAD in children and adolescents. Also included are current prevalence data on SAD--several reports in this volume suggest it may occur in approximately 5% of the population with subclinical disturbances present in even more individuals. Reports on seasonal changes in the normal population consider whether the mood and personality changes observed in SAD are extremes of normal human seasonality and whether the disorder's pathophysiology is actually on a continuum with a range of biological seasonal changes found in the general population. A neurological theory is presented that maps the basic systems involved in mobilizing behavior and engaging the organism with its environment. The theory is then applied to seasonal changes both in normal motivated behavior and in SAD. Points of consensus as well as points of contention are given balanced consideration in the book's chapters, which address several unresolved questions concerning phototherapy's mechanism of action. Among these controversial areas are the assessment of placebo effect, choice of placebo control, and the importance of the timing of light treatment to its antidepressant effect. Also discussed are the circadian phase shift theory of SAD, the melatonin hypothesis, and other current theories. There is substantial agreement among clinical researchers that SAD is a common condition, and that, in a large percentage of cases, symptoms of winter depression can be ameliorated by treatment with environmental light. Beyond these fundamental points of agreement, however, many aspects of SAD remain controversial. This timely, authoritative compilation provides all clinicians and researchers with a comprehensive update on important, new investigations on this intriguing disorder.