Subthalamic nucleus in patients with Parkinson's disease encodes changes and magnitude of applied force

The subthalamic nucleus (STN), a primary target for Parkinson's disease (PD) neuromodulation therapies, contributes to movement dynamics but it is unknown how STN relates to specific kinematic parameters. We investigated the neuronal activity in the dorsolateral STN during a visually cued isometric grip-force task in the contralateral hand in patients with PD who were undergoing deep brain stimulation surgery. Patients applied various levels of grip force during a task that separated a sustained applied force vs periods of changing force (yank) while we recorded single unit activity with a microelectrode. We found significant force-related changes in STN unit activity, especially immediately after force onset and offset, but minimal changes during movement preparation. Significant changes in single unit activity occurred with changes in grip force (squeeze and release) as well as during sustained grip force. During sustained force, the discharge rate positively correlated with force magnitude. During a phase of the task when force changes (squeeze or release), some units' firing rate increased, some decreased, and some had mixed responses. Units with increased firing rates during squeeze had later latencies than those with decreased rates. Most changes in firing rate followed changes in force.