Role of right dorsolateral prefrontal cortex-left primary motor cortex interaction in motor inhibition in Parkinson's disease.

Background: Impaired motor inhibition in Parkinson's disease (PD) is associated with functional alterations in the frontal-basal ganglia (BG) neural circuits. The right dorsolateral prefrontal cortex (DLPFC), pre-supplementary motor area (pre-SMA), and primary motor cortex (M1) play key roles in regulating this inhibition. However, the changes in interhemispheric interactions during motor inhibition in PD have not been clearly defined.

Methods: We used dual-site paired-pulse transcranial magnetic stimulation (ppTMS) to examine the interactions between the right DLPFC and pre-SMA and the left M1 in 30 patients with early-stage PD and 30 age-matched healthy controls (HC) during both resting and active conditions, specifically while performing a stop-signal task (SST).

Results: Stop-signal reaction times (SSRT) were significantly longer in PD patients compared to HC. The right DLPFC-left M1 interaction, at both short- and long-latency intervals, showed enhanced inhibition in PD following the stop-signal. In PD patients, SSRT was correlated with the inhibition of the right DLPFC-left M1 interaction, with stronger inhibition associated with shorter SSRT.

Conclusion: The deficit in reactive inhibition observed in PD is linked to an abnormal modulation of the right DLPFC-left M1 interaction during the stopping process.