Although it commonly includes changes in mood, energy, appetite, and sleep, these changes can be very different in different people. Some people appear to have overactivity of the appetite system and others appear to have underactivity, resulting in eating too much or too little, respectively. Likewise, some people can sleep too much and others can’t sleep enough. Distilling depression into distinct symptoms, some that represent overactive or underactive brain regions, is likely to be the most effective and accurate way to understand depression,
