Depression is both a brain disorder and a state of mind. The brain is unique—it is the only organ whose function we consciously experience because the brain is the organ of the mind. Illnesses of the mind-brain affect tens of millions of people in the United States. Depression is by far the most prevalent, representing 99% of all mind-brain illness.
The influx of cortisol triggered by depression also causes the amygdala to enlarge. This is part of the brain associated with emotional responses. When it becomes larger and more active, it causes sleep disturbances, changes in activity levels and changes in other hormones.
Around about 264 million people of all ages suffer from depression. Depression is the leading cause of disability world wide and is a major contributor to the overall global burden of the disease. ( More Women are affected by depression than men)