Objective: This study aims at finding a correlation between the activity of single neurons of the subthalamic nucleus (STN) in Tourette Syndrome (TS) patients and the optimal site for Deep Brain Stimulation (DBS) to suppress TS motor symptoms.

Background: TS is characterized by motor and vocal tics that tend to wax and wane in severity and frequency. The dysfunctional activity in STN underlying pathological behavior in TS is still to be completely understood: the current model does not account for any relevant involvement of the STN [1], and largely relies on animal experiments.

Method: Here, we describe for the first time neural activities of STN in TS patients acquired through microrecordings during DBS procedures. Four TS patients (34.2 years range 24-47) and two patients with Parkinson disease (PD) underwent bilateral STN implant. Continuous physiological recordings under general anesthesia were performed from 10 mm above the target to 1/2 mm below it, with 0.5 mm steps along the single planned trajectory. We characterized the discharge pattern of each isolated single unit activity (n = 125 for TS, n=54 for PD) computing the mean firing rate (MFR) and a burstiness index [2].

Results: In all TS patients, a sustained acute tic improvement was observed following stimulation of STN-located contacts (> 60% YTGSS improvement, P <0.001). We did not found significant MFR and spectral density differences between TS and PD cells. Spike patterns analysis revealed instead a larger fraction of bursting cells in TS than in PD (39/125, 31.2% vs. 4/54, 7%; P<0.001). These bursting units in TS STN were reliably more present at the depth for witch the clinical effect was maximum (>50 % within ±2 mm from optimal DBS target site).

Conclusion: STN in TS presents depth-specific neural bursting properties with a significantly higher density close to the optimal clinical DBS target. This information can help determining the optimal DBS target and clarifying the relationship between TS tics and pathological firing patterns.

References: [1]. Yael D, Vinner E, Bar-Gad I. Pathophysiology of tic disorders. Mov. Disord. 105; 30: 1171- 1178. [2]. Mochizuki Y, Onaga T, Shimazaki H. et al. Similarity in neural firing regimes across mammalian species. J. Neurosci. 2016; 36(21): 5736-5747.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/firing-pattern-of-single-neurons-in-the-subthalamic-nucleus-of-tourette-syndrome-patients-identifies-optimal-deep-brain-stimulation-target-site/