Many of us experience mood shifts during the colder, shorter, and gloomier winter days. However, for those diagnosed with seasonal affective disorder (SAD), winter blues take on a whole new meaning. While mental health professionals have attributed the symptoms of SAD, which include depression and a feeling of hopelessness, to the lack of sunlight, no one was sure how the brain made the connection. Now, some researchers have found the culprit – a brain circuit which connects special light-sensing cells in the retina with the areas of the brain that impact our moods.