Brain mechanisms in manic depression.

Manic depressive illness (bipolar disorder) is the mood disorder classically considered to have a strong biological basis. During manic depressive cycles, patients show dramatic fluctuations of mood, energy, activity, information processing, and behaviors. Theories of brain function and mood disorders must deal with the case of bipolar disorder, not simply unipolar depression. Shifts in the nosologic concepts of how manic depression is related to other mood disorders are discussed in this overview, and the renewed adoption of the Kraepelinian "spectrum" concept is recommended. The variable clinical presentations of manic depressive illness are emphasized. New genetic mechanisms that must be considered as candidate factors in relation to this phenotypic heterogeneity are discussed. Finally, the correlation of clinical symptom clusters with brain systems is considered in the context of a three-component model of manic depression.