Seasonal Affective Disorder (SAD) is a subtype of Major Depressive Disorder, characterized by a recurrent temporal relationship between the season of year, the onset and the remission of a major depressive episode. Estimates of the annual prevalence state that 1-6% of the population will develop SAD with the larger prevalences found at greater extremes in latitude. SAD is most likely triggered by the shortening photoperiod experienced in the winter months leading to a deterioration of mood. Recent cross-sectional neuroimaging studies have found cellular and neurotransmitter changes in response to seasonality, ultimately having an impact on the affect of patients. Conversly, this study aims to investigate the changes in neurocircuitry related to depression and euthymic states. Patients with SAD offer a unique ability to study these changes since they have predictable triggers for the onset of depression (i.e. the winter months) and remission (i.e. the summer months).