This paper discussed research investigating the types of depression. The research found evidence for at least six subtypes of depression, which were each generated by abnormal activity in a distinct set of brain circuits that regulate mood and cognition. One subtype affects a constellation of brain regions that generates aimless mental chatter when the brain is "in idle" and can lead to unrelenting negative thoughts. Another type dampens reward networks, robbing a person of the ability to feel pleasure, (anhedonia). These two subtypes, along with a third called cognitive control often respond poorly to depression treatments. The highest risk groups are those in the anhedonia and cognitive control groups, which both have an elevated suicide risk.