Human Ventral Intermediate Nucleus Beta Power Decreases Are Associated with Failure to Inhibit an Unwanted Action

Introduction: The Ventral Intermediate Nucleus (VIM) has been a therapeutic target for Deep Brain Stimulation (DBS) for over 30 years. Yet relatively little is known about the mechanisms by which the VIM influences movement. This limited insight partially stems from the fact that traditionally, human electrophysiological recordings were limited to the short perioperative time window while patients underwent DBS implantation surgery. To further understand the VIM's role in response execution and inhibition, we used a chronically implanted Percept battery to record VIM activity while patients participated in a response inhibition task.

Methods: We recorded local field potentials from the VIM of 6 Essential Tremor patients (n=12 VIMs) while they participated in the Stop Signal Reaction Time Task. This task involves Go trials in which a voluntary movement is executed, Stop-Correct trials, in which a planned movement is intentionally cancelled, and Stop-Error trials, in which the subjects fail to respond to a stop cue and erroneously execute a response.

Results: Similar to changes we recently reported in the Subthalamic Nucleus (STN) during the task, we observed a movement-related decrease in VIM beta power and a Stop-Signal-related increase in VIM theta power. Prior to the trial onset, however, the trials that would go on to become a Stop-Error trial showed significantly lower baseline VIM beta power than the trials that would go on to be a Stop-Correct trial. Furthermore, after each trial ended, we observed a significantly higher beta power rebound following the Go trials relative to the rebound observed on Stop trials.

Conclusion : We have that shown VIM and STN beta oscillations may play separate yet complimentary roles during the same task. Whereas the STN seem to be related to response inhibition on the current trial, the VIM seems to be involved during the time in between trials, when subjects are executing across-trail behavioral adaptations.