Subthalamic DBS does not restore deficits in corticospinal suppression during movement preparation in Parkinson's disease

Objective: Parkinson's disease (PD) patients exhibit changes in mechanisms underlying movement preparation, particularly the suppression of corticospinal excitability – termed “preparatory suppression” – which is thought to facilitate movement execution in healthy individuals. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) being an attractive treatment for advanced PD, we aimed to study the potential contribution of this nucleus to PD-related changes in such corticospinal dynamics.

Methods: On two consecutive days, we applied single-pulse transcranial magnetic stimulation to the primary motor cortex of 20 advanced PD patients treated with bilateral STN-DBS (ON vs. OFF), as well as 20 healthy control subjects. Motor-evoked potentials (MEPs) were elicited at rest or during movement preparation in an instructed-delay choice reaction time task including left- or right-hand responses. Preparatory suppression was assessed by expressing MEPs during movement preparation relative to rest.

Results: PD patients exhibited a deficit in preparatory suppression when it was probed on the responding hand side, particularly when this corresponded to their most-affected hand, regardless of their STN-DBS status.

Conclusions: Advanced PD patients displayed a reduction in preparatory suppression which was not restored by STN-DBS.

Significance: The current findings confirm that PD patients lack preparatory suppression, as previously reported. Yet, the fact that this deficit was not responsive to STN-DBS calls for future studies on the neural source of this regulatory mechanism during movement preparation.