Cortical beta power modulation is asymmetric and reduced during movement execution and inhibition in Parkinson's disease

Inability to initiate movements is a cardinal feature of Parkinson's disease (PD), but inhibitory motor control is also impaired. Cortical electrophysiologic spectral patterns of these processes are still poorly understood. We investigated cortical electrophysiology during movement planning, execution and proactive inhibition in patients with PD. We hypothesized that in the healthy state, proactive inhibition is accompanied by increased beta band activity in the right frontal cortex, and that this process is impaired in PD patients. We recorded 64-channel EEG in 20 moderately advanced PD patients, off and on levodopa, and 20 age-matched healthy controls during cued Go and Go/NoGo tasks and performed spectral time-frequency analysis. PD patients exhibited prolonged response times, more errors and altered cortical activity patterns compared to controls. Levodopa improved movement execution in a simple Go task, but impaired proactive inhibition in a more complex Go/NoGo task. Spectral EEG analysis during movement planning and execution (Go task) showed reduced beta power modulation in PD patients particularly in the more impaired hemisphere, off and on levodopa. When proactive inhibition was engaged (Go/NoGo task), beta power over the right lateral frontal cortex was higher (i.e. decreased less compared to Go task) in healthy controls than in PD patients on medications. In conclusion, PD patients exhibit decreased and asymmetric beta power modulation over the sensorimotor cortex during movement. Proactive inhibition is associated with elevated beta activity over the right lateral frontal cortex in healthy controls, and this pattern is attenuated in PD patients in conjunction with a behavioral inhibitory deficit.