Photoperiod Links to Serotonin Neurons (IMAGE) Vanderbilt University Caption Illustration shows the links between the brain's serotonin system, circadian clock and pineal gland which are involved in seasonal affective disorder, depression and other serious mood disorders. Credit Courtesy of Chris Ciarleglio, Brown University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.