Objective: To investigate electrophysiologic characteristics of sensorimotor cortical activity in patients with Parkinson’s disease (PD) undergoing globus pallidus deep brain stimulation (GPi DBS) or radiofrequency ablation.

Background: PD is characterized by increased neural synchronization throughout the basal ganglia-thalamo-cortical network. Previous work showed that subthalamic DBS reduces cortical synchronization measured as phase-amplitude coupling (PAC). We hypothesized that GPi DBS and pallidotomy would similarly reduce cortical PAC given that these procedures result in a comparable therapeutic benefit.

Methods: We measured local field potential activity over the arm area of the sensorimotor cortex using a temporary 6-electrode subdural strip in patients who underwent pallidal DBS or ablation. PAC was calculated between beta and broadband gamma at rest. In a subset of patients, cortical evoked potentials were recorded during low frequency DBS to characterize neural pathways activated by DBS.

Results: We report results from 12 patients undergoing GPi DBS (14 hemispheres recorded) and 1 patient undergoing unilateral pallidotomy. Significant beta-broadband gamma PAC was detectable in 11/15 hemispheres over the primary motor cortex at rest. During therapeutic DBS, PAC decreased in 8/11 hemispheres by 45% on average (10-79%). In two tremor-dominant patients, PAC increased during therapeutic stimulation (3/11 hemispheres). In the pallidotomy patient, PAC reversibly decreased during test stimulation and remained low after permanent lesioning. In addition, a persistent ∼75 Hz narrow band peak appeared after lesioning. Low frequency GPi DBS in 3 patients evoked cortical potential between 17-22 ms after the stimulus pulse indicating a multi-synaptic pathway to the cortex.

Conclusions: In rigid-akinetic PD, pallidal DBS decreases phase amplitude coupling in the primary motor cortex, similarly to what has been observed in STN DBS. In patients with significant tremor PAC may actually increase, possibly because tremor movement is suppressed by stimulation. PAC reduction does not depend on existence of direct cortical projections into the stimulated nucleus. Pallidotomy causes a persistent decrease in PAC and results in emergence of a narrow band peak in the gamma frequency range.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/pallidal-dbs-and-pallidotomy-alter-cortical-synchronization-in-parkinsons-disease/