It has been hypothesized that, in humans, the inhibitory control of manual movements relies upon a right-lateralized frontal–basal ganglia–thalamic pathway, comprising two areas of the right frontal cortex, the inferior frontal gyrus and pre-supplementary motor area, which would control movement initiation acting through the right subthalamic nucleus (STN).

We directly assessed the role of the right STN via a task requiring withholding of planned arm movements in response to the presentation of an infrequent stop signal (countermanding task), in 10 Parkinson's patients receiving high-frequency electrical stimulation of the STN of both hemispheres (deep brain stimulation; DBS). We compared the performance of patients during the countermanding task in four experimental conditions: DBS-ON, DBS-OFF, DBS-OFF right and DBS-OFF left. We found that turning off the right, the left or both DBS affected arm response inhibition in the same way, by significantly increasing the reaction time to the stop signal (SSRT) with respect to the condition in which both DBS were ON. Furthermore, the SSRT measured in 13 age-matched healthy subjects was not significantly different from that in Parkinson's patients when both DBS were ON, but was shorter than in all other DBS conditions.

Thus we demonstrated equal contributions of left and right STN to the control of arm movement suppression and that the inhibitory control is restored to an approximately normal level only when both DBS are ON.