Seasonal affective disorder, Part I: A review of the neural mechanisms for psychosocial nurses.

This article is the first of a two-part series on Seasonal Affective Disorder (SAD). Mental health and nursing researchers are beginning to investigate the implications of seasons on mood and mood states. Delineation of SAD and its treatment by phototherapy is an example. This article reviews the pertinent research regarding the hypothesized neural mechanisms of SAD. Three competing hypothesis are contrasted and compared: the melatonin hypothesis, the phase delay hypothesis, and the photon counting hypothesis. Although no one theory is universally accepted, current data supports the phase delay hypothesis and suggests that morning phototherapy is the most effective treatment.