Differences in neurobiological pathways of four "clinical content" subtypes of depression.

Although often considered as a mental disorder, depression is best described as a behavioral-neurobiological phenomenon. In addition, although usually reported as a unitary diagnosis, major depressive episode is composed of a range of different symptoms that can occur in nearly 1500 possible combinations to fulfill the required diagnostic criterion. To investigate and describe the underlying behavioral and neurobiological substrates of these symptoms, they were clustered into "clinical content" subtypes of depression according to their predominant common behavioral characteristics. These subtypes were then found to possess different neurobiological pathways that argue for different treatment approaches.