The primate substantia nigra and VTA: integrative circuitry and function.

A substantial amount of research has focused on the midbrain dopamine system and its role in mediating a wide range of behaviors. In diseases in which dopamine function is compromised, patients exhibit a constellation of symptoms suggesting that the dopamine system plays an important role in the integration of several functions. We have shown that there are subgroups of dopamine neurons that receive information from limbic and association areas and project widely throughout cortex and striatum, including motor areas. A dorsal tier of dopamine neurons receive input from the ventral (limbic) striatum and the amygdala and project widely throughout cortex. A more ventrally located group of dopamine cells receives input from both the limbic and association areas of striatum and project widely throughout the striatum including the sensorimotor regions. Through these projections the dopamine system can effect a wide range of behaviors. For the most part, structures of the basal ganglia are thought to be organized in parallel pathways. However, the behaviors affected by basal ganglia disorders can be in part explained by the integrative nature of the dopamine system and its links to motor, limbic, and association areas of the striatum and cortex.