Insular and gustatory inputs to the caudal ventral striatum in primates.

The ventral striatum mediates goal-directed behaviors based, in part, on inputs from the amygdala. However, striatal areas caudal to the ventral striatum also receive inputs from the amygdala. In primates, the amygdala projects to the central ventral putamen, lateral amygdalostriatal area, and caudal ventral putamen, suggesting that these regions are also "limbic-related." The anterior insula, which integrates sensory and amygdaloid inputs, projects to the classic ventral striatum. We used retrograde and anterograde tract tracing techniques to determine the extent to which specific subdivisions of the insula influence the caudal ventral striatum in the primate. The anterior (agranular and rostral dysgranular) insula has significant inputs to caudal ventral striatal regions that receive projections from the amygdala. In contrast, the posterior (granular) insula has sparse projections. Within the agranular insula, the posteromedial agranular (Iapm), lateral agranular (Ial), and posterolateral agranular (Iapl) subdivisions have the strongest inputs. These subdivisions mediate olfactory, gustatory, and visceral information processing (Carmichael and Price JL [1996b] J. Comp. Neurol. 363:642-640). In contrast, the intermediate agranular subdivision (Iai) is relatively devoid of visceral/gustatory inputs and has few inputs. In summary, caudal ventral striatal areas that receive amygdaloid inputs also receive significant innervation by agranular and dysgranular insula subdivisions that are themselves connected with the amygdala. Within this projection, the Ial, Iapm, and Iapl make the strongest contribution, suggesting that highly processed visceral/autonomic information, taste, and olfaction influence behavioral responses mediated by the caudal ventral striatum.