Depression symptomatology and neurobiology.

The DSM-IV-TR distinguishes major depressive disorder (MDD) from normal sadness and grief by requiring a certain duration and number of symptoms that cause impairment and dysfunction. Depression is considered a heterogeneous condition in which different biologic abnormalities may be responsible for problems with sleeping, eating, energy, and emotional reactions. Neuroimaging, pharmacology, and genomics are among the sources of information that have contributed to theories about the pathophysiology of MDD and may lead to truly personalized medicine in the future.