The condition we now know as seasonal affective disorder (SAD) was first recognized in the early 1980s, when some patients were noted to have symptoms of depression only during the winter months. How does seasonal depression differ from other conditions such as major depression or bipolar disorder? Dr. Norman Rosenthal, a former senior researcher in psychiatry and psychobiology at the National Institute of Mental Health and one of the world's foremost experts on SAD, details the clinical profile of this disorder and describes light therapy and other potential treatments with host Dr. Jennifer Shu. Because there are some similarities between SAD and full depression, is it possible that light therapies or other SAD treatments would be effective for patients with year-round symptoms or bipolar disorder?