Cooperative role of the nucleus accumbens shell and core in behavioral adaptation to environmental change

The nucleus accumbens (NAcc) plays a crucial role in mediating the organization and regulation of goal-directed behavior for the sake of reward acquisition. Histochemical and anatomical studies have revealed that the NAcc consists of core and shell regions. However, the functional differences between NAcc core and shell neurons with respect to their contribution to the performance of goal-directed behavior remain unclear. To reveal the functional differences, we conducted electrophysiological experiments in which we made recordings from the NAcc core and shell of rats performing a task for a reward. The core neurons made phasic discharges during the behavioral phases of the task. By contrast, in the shell, some of the neurons did not show any selective activity change in response to each behavioral phase, but when changing the reward contingency disrupted the habituated task behavior, the discharge rate increased spontaneously. From these results, we conclude that the NAcc shell contributes to regulating behavior by searching for adaptive behavior when the existing behavior is rendered inadequate by environmental change, and the core contributes to executing the acquired adaptive behavior properly.