Objective: The aim of the current study is to characterize the neuronal activity of the pallidal area which gives the best benefit following unilateral deep brain stimulation (DBS).

Background: Bilateral DBS of globus pallidus (GPi) is an accepted and most common treatment for medically refractory cervical dystonia (CD). Few case reports showed that unilateral procedures can be effective in some patients. Although the mechanisms of clinical improvement in CD following unilateral or bilateral pallidal DBS remain unclear. Previously we showed that asymmetrical pallidal activity is correlated with the degree of involuntary head turning and results in asymmetric feedback to head neuronal integrator causing its dysfunction [1].

Method: We assessed 4 patients with CD who underwent implantation of bilateral GPi-electrodes. We provided patients with different variants of DBS settings, which included bilateral or unilateral for each hemisphere stimulation. In all 4 patients, a unilateral GPi-DBS was effective with an average TWSTRS improvement 57±8%. We used intraoperative microelectrode recording and performed the analysis of the spontaneous activity of 304 pallidal neurons in both (GPi and GPe) segments. For each cell, we calculated the firing rate, coefficient of variance, and other parameters.

Results: At first, we compared characteristics of unit activity in the GP which is effective for unilateral DBS (ON-Side) and the opposite side (OFF-Side). We found that the firing rate in ON-Side was significantly higher in GPe and lower in GPi than OFF-Side. The opposite differences were observed in oscillation scores in gamma and high gamma bands. We also analyze neuronal activity in ON-Side pallidal areas which is most effective for stimulation. These areas are characterized by a more bursty pattern with higher oscillation scores in the theta band. Finally, we showed that the effectiveness of unilateral DBS depends on the pallidal asymmetry amplitude.

Conclusion: Our findings indicate that unilateral DBS stimulation could be effective for lateralized CD patients with asymmetrical pallidal activity. Characteristics of pallidal activity could be a useful electrophysiological marker for the selection of stimulated areas. Further studies of unilateral DBS mechanisms are needed. This study was supported by Russian Science Foundation (18-15-00009, Sedov) and partly by Russian Foundation for Basic Research (20-015-00438, Semenova).

References: 1. Sedov, A., Usova, S., Semenova, U., Gamaleya, A., Tomskiy, A., Crawford, J. D., … & Shaikh, A. G. (2019). The role of pallidum in the neural integrator model of cervical dystonia. Neurobiology of Disease, 125, 45-54.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/pallidal-single-unit-activity-in-cervical-dystonia-patients-with-unilateral-deep-brain-stimulation/