The Basal Ganglia Do Not Select Reach Targets but Control the Urgency of Commitment.

Prominent theories of decision making suggest that the basal ganglia (BG) play a causal role in deliberation between action choices. An alternative hypothesis is that deliberation occurs in cortical regions, while the BG control the speed-accuracy trade-off (SAT) between committing to a choice versus continuing to deliberate. Here, we test these hypotheses by recording activity in the internal and external segments of the globus pallidus (GPi/GPe) while monkeys perform a task dissociating the process of deliberation, the moment of commitment, and adjustment of the SAT. Our data suggest that unlike premotor and motor cortical regions, pallidal output does not contribute to the process of deliberation but instead provides a time-varying signal that controls the SAT and reflects the growing urgency to commit to a choice. Once a target is selected by cortical regions, GP activity confirms commitment to the decision and invigorates the subsequent movement.