Beyond the Brake: the Subthalamic Nucleus Predominantly Facilitates Action in Non-human Primates.

The subthalamic nucleus (STN) is traditionally viewed as a brake on motor output. Challenging this model, we investigated its role in value-based decision-making by recording single-neuron activity from the primate STN during a choice task. Our findings reveal that the STN contains functionally distinct clusters of neurons and, contrary to its classical role, the vast majority of task-related neurons (approximately 89%) exhibited activity consistent with action facilitation. Two of the clusters contained facilitative neurons that increased their firing for rewarded choices, and critically, their response latency predicted saccadic reaction times on a trial-by-trial basis. Population-level analyses further demonstrated that these facilitative neurons robustly encode the upcoming choice. A smaller third cluster of neurons showed activity consistent with action suppression. These results indicate a dual function of the STN, suggesting it plays a predominant role in actively facilitating desired actions, rather than simply suppressing unwanted ones.