Influence of Light Exposure on Cerebral MAO-A in Seasonal Affective Disorder and Healthy Controls Measured by PET

Inclusion Criteria for Patients: * DSM-IV diagnosis of SAD established by diagnostic interview according to the SCID. * Global Seasonality Score of 10 or higher on the Seasonal Pattern Assessment Questionnaire (SPAQ) * Somatic health based on history, physical examination, ECG, and laboratory screening * Aged 18 to 55 years * No therapeutic treatment of SAD in the last 6 months (drugs and light therapy) * Willingness and competence to complete the informed consent process Inclusion criteria for healthy controls: * Aged 18 to 55 years * Somatic and psychiatric health based on history, physical examination, ECG, laboratory screening, SCID * Willingness and competence to complete the informed consent process Exclusion criteria for patients and healthy controls: * Concomitant major medical or neurological illness * Concomitant psychiatric disorders * Current smoking * Ingestion of antidepressants or other psychotropic agents targeting the serotonergic system, within the last 6 months. * Bright light therapy within the last 6 months. * Current substance abuse including alcohol, drugs of abuse, or any medication in a manner which is indicative of substance-related disorders (e.g. substance dependency) according to the DSM-IV. * Failure to comply with the study protocol or follow the instructions of the investigators. * Positive urine pregnancy test. * For participants who participated in an earlier neuroimaging study using ionizing radiation, the total radiation exposure dose of 20 mSv over the last 10 years must not be exceeded, as specified in the legislation on radiation protection (Allg. Strahlenschutzverordnung 2010; www.ris.bka.gv.at).