Dopamine, but not serotonin, regulates reversal learning in the marmoset caudate nucleus.

Studies of visual discrimination reversal learning have revealed striking neurochemical dissociations at the level of the orbitofrontal cortex (OFC) with serotoninergic, but not dopaminergic, integrity being important for successful reversal learning. These findings have considerable implications for disorders such as obsessive compulsive disorder and schizophrenia, in which reversal learning is impaired, and which are primarily treated with drugs targeting the dopaminergic and serotoninergic systems. Dysfunction in such disorders however, is not limited to the OFC and extends subcortically to other structures implicated in reversal learning, such as the medial caudate nucleus.