In her book "This is Depression: A Comprehensive, Compassionate Guide for Anyone who Wants to Understand Depression," psychiatrist Dr. Diane McIntosh offers a new theory about the cause of depression. While the mental health condition has long been considered to be a chemical imbalance in the brain, McIntosh argues that depression is a disease caused by the body's immune system, brought on by chronic stress and hormonal dysregulation. McIntosh joins Gormley now to discuss depression and the new book.