"Basal ganglia mechanisms of reward-based and instruction-based decision-making."
Abstract: The basal ganglia contain parallel neural circuits: direct, indirect, and hyperdirect pathways. A popular hypothesis is that these pathways work in a coordinated manner to select a desired action while suppressing undesired actions. However, critical evidence to support this hypothesis had been lacking until recently. Based on our recent experiments using trained monkeys, we propose that the direct and indirect pathways select actions based on motivational demands, whereas the hyperdirect pathway selects actions based on cognitive demands. The direct pathway, which consists of two serial inhibitory connections, serves to acquire actions that lead to rewarding outcomes. The indirect pathway, which consists of three inhibitory connections, serves to discourage actions that lead to punishing or non-rewarding outcomes. Dopaminergic inputs to the STR are crucial in implementing motivational values in the signals transmitted in these pathways. In contrast, the hyperdirect pathway, which is mediated by the direct cortical connection to the subthalamic nucleus, serves to select one action that is in conflict with others, especially for switching from an automatic action to a controlled action. Inputs from outside the basal ganglia, especially those from the lateral habenula and the dorsal raphe (including serotonin neurons), fine-tune or modify the operation of the basal ganglia circuits.