Objective: 1. Method development to routinely determine cortical responses evoked by stimulation of the subthalamic nucleus (STN-EP) during intraoperative electrode placement for STN deep brain stimulation (DBS) in Parkinson´s disease (PD). 2. Electrophysiological characterization of STN-EP to potentially develop an intraoperative biomarker to improve target determination in STN-DBS.

Background: STN-DBS is highly effective to alleviate motor symptoms in PD. It has been shown that clinically effective STN-DBS may require a certain anatomical proximity of the electrode to the monosynaptic connection between the mesial cortical pre-motor region and the STN (hyperdirect pathway, HDP). STN-EP may functionally characterize the HDP that we here investigate whether STN-EP could serve as in intraoperative marker for target determination in STN-DBS.

Method: During the routine implantation procedure for STN-DBS, STN-EP were elicited by stimulation above and within the STN proper via the uninsulated tip of the guiding tubes of the microelectrodes (simultaneous insertion of up to five microelectrodes; macrostimulation: 2,5mA, 100µs, 5Hz; Neuromaster, Nihon Kohden). Recordings of STN-EP were achieved by subcutaneous scalp electrodes (EEG 10/20: F (3/4), Fz, C (3/4), Cz). An additional electrode (“delta”) was placed above the stereotactically determined individual cortical projection of the HDP (MRI tractography). Microelectrode recordings (MER) were used to determine dorsal and ventral STN boundaries to classify stimulation site for STN-EP (inside STN versus outside STN).

Results: (preliminary data of our first six patients): STN-EP show a polyphasic configuration, consisting of three short latency potentials: EP1 (n=87): 2,2±0,0ms (SEM), EP2 (n=73): 4,6±0,1ms and EP3 (n=90): 8,4±0,2ms followed by a long latency potential >20ms. Stimulation within the STN proper led to higher amplitudes than stimulation outside the nucleus (MannWhitney-U-Test, p < 0,001).

Conclusion: Intraoperative macrostimulation of the STN region led to polyphasic cortical potentials which are supposed to be transmitted via the HDP (Miocinovic et al., J Neuroscience 2018). Our data suggest that properties of STN-EP vary on stimulation site of the STN region so that STN-EP may be a promising marker for intraoperative target determination and verification in STN-DBS.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cortical-responses-evoked-by-stimulation-of-the-subthalamic-nucleus-for-intraoperative-target-determination-in-deep-brain-stimulation/