(27) Electrophysiologic Mechanisms of Movement Initiation and Response Inhibition in Parkinson’s Disease

Introduction: How sensorimotor cortical regions encode movement planning, initiation and inhibition are not well understood in Parkinson's disease (PD). We hypothesized that sensorimotor cortex beta power is reduced during motor planning and this reduction corelates with response time, but the effect is less pronounced when proactive inhibition is required.

Methods: Utilizing subdural electrocorticography (ECoG) over sensorimotor cortex, recordings were collected from PD patients engaging in GoNoGo (GNG) task while undergoing awake deep brain stimulation surgery. Patients performed 120 trials of GNG task and 45 trials of GoOnly (GO) task (control task, response always expected). Each trial consisted of 3 time points: Fixation (start of trial), Cue (indication if left- or right-hand response will be required), Go/NoGo (press button or withhold). We performed Morlet wavelet analysis on the ECoG signal zeroed at the Go/NoGo signal of both tasks, specifically focused on the beta band (13-30 Hz). Two bipolar ECoG channels, one over primary motor cortex (M1) (closest to the hand knob area) and the other over the premotor area were analyzed. Average beta power was calculated between the cue and go signal (planning period) as well as 250 ms before and after the median response time (execution period).

Results: Our study included 13 PD patients (age: 57.6±8.5; 10M/3F; MDS-UPDRS III off-med: 47.2±12.0). Median reaction time was 372±133 ms during GO task compared to 456±107 ms during GNG task which was significantly different (p=0.002). The response time for GO task was significantly correlated with motor disease severity measured by MDS-UPDRS III score (p=0.022, R2=0.424), but not for GNG. For M1 channel, median reaction times were positively correlated with average beta power during the planning period for GO (p=0.01, R2=0.499) and GNG task (p=0.001, R2=0.755). The beta power during execution was lower (more desynchronized) in the GO compared to GNG task (p=0.019), but did not correlate with response times. For premotor channel, median reaction times did not correlate with the average beta power during the planning period, but beta power was significantly lower in GO compared to GNG task (p=0.014).

Conclusion: Our preliminary findings indicated that patients with less beta desynchronization in the primary motor cortex during movement preparation respond slower. Proactive inhibition significantly reduced beta desynchronization in the premotor area during movement planning as well as primary motor area during movement execution. Modulating cortical beta power may therefore improve transition between movement planning and execution.