326 Characterization of Synchronization Between Globus Pallidus Neurons and Motor Cortex in Parkinson's Disease
Abstract INTRODUCTION Excessive oscillatory neuronal synchronization throughout the basal ganglia thalamocortical motor loop is a hallmark of the Parkinsonian state. This may manifest as spike-spike correlations, coherence between field potentials, or spike-field interactions within or between structures in the circuit. Globus pallidus occupies a central role in basal ganglia processing, but neither internal (GPi) nor external (GPe) globus pallidus is monosynaptically connected to motor cortex. Understanding patterns of M1-pallidal synchronization will provide insight into the possible different roles of GPi and GPe stimulation, compared to STN stimulation, in ameliorating the excessive neuronal synchronization in PD. METHODS Using subdural electrodes and high resolution electrocorticography (ECoG) contacts temporarily placed over motor cortex during DBS implantation and microelectrode recordings, we evaluate the strength and topography of synchronization between pallidal neurons and cortical ECoG potentials in 16 PD patients. RESULTS >Recording from 59 GPe and 42 GPi cells with cortical ECoG field potentials demonstrated that 17% of GPe and 12% of GPi neurons showed significant interactions associated with cortical recording sites approximately 25 mm from midline. For those pairs with significant interactions, peak of the spike-triggered average potentials occurred within 100ms prior to spike time. GPe neurons showed maximum coherence with M1 in the beta (13-30 Hz) frequency range while GPi neurons had maximum coherence in the alpha (8-12 Hz) range. CONCLUSION Topography of significant M1-pallidal interactions is consistent with tractography findings showing more mesial areas of M1 to dominate cortical-basal ganglia anatomic connectivity. The observation that GPe stimulation is more “prokinetic” than GPi stimulation may be explained by the finding that GPe is more synchronized to the cortex in beta frequencies than GPi, as disruption of beta oscillation is important in ameliorating akinesia.