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(49) Optimizing Motor Thalamus Deep Brain Stimulation to restore face and upper limb motor functions

Friday, June 13, 2025
5:10 PM - 5:50 PM ET
Location: Sky View
Introduction: In the United States alone, approximately 2.5 million individuals experience chronic upper limb deficits1, while over 1 million struggle with facial motor and speech impairments2 following neurological injuries. Deep brain stimulation of the motor thalamus (mT-DBS) has been shown to enhance cortical motor output to the face and upper limb in both non-human primates3 and humans3,4. However, the optimal stimulation parameters and thalamic targets that maximizes this motor facilitation remain unclear. We addressed this by characterizing the effects of different stimulation target locations and frequencies in intraoperative surgical patients (n=16, 32 hemispheres) and validating these findings in two individuals with chronic mT-DBS implants who had upper limb and orofacial motor deficits

Methods: We mapped neural activity in patients undergoing DBS implantation in the motor thalamus to treat essential tremor within three motor thalamus nuclei—ventral oralis posterior (VOP), ventral oralis anterior (VOA), and ventralis intermediate (VIM) at multiple depths along the electrode trajectory, while patients performed upper limb, facial, or speech tasks. We then recorded motor-evoked potentials (MEPs) induced by direct cortical stimulation (DCS) of the primary motor cortex (M1), in both facial and upper limb muscles while stimulating the different thalamic nuclei at different frequencies. Lastly, we tested the optimal stimulation configurations to facilitate motor activity in two individuals chronically implanted with DBS leads in the motor thalamus (P1: 70yo with subcortical stroke; P2: 45yo with TBI). Motor performance, muscle activity, and movement kinematics were assessed under different stimulation protocols targeting specific thalamic nuclei and at different frequencies.

Results: while VOP and VIM nuclei appeared to equally represent upper limb and facial movements, the VOA primarily represented orofacial movements and speech-related activity. VOP neurons displayed the highest firing rates across all nuclei, suggesting a crucial role in movement generation, further supported by diffusion tensor imaging (DTI) reconstructions highlighting dominant projections from the VOP to M1. As previously shown3, low-frequency stimulation (50–80 Hz) in the VOP more consistently potentiated DCS-MEPs than high-frequency, linked to a higher degree of DCS-MEP suppression. In the two chronically implanted patients, low-frequency stimulation and electrode configurations designed to target the VOP resulted in increased in upper limb motor performance and improved facial/speech functions during standardized clinical tests.

Conclusion: These findings suggest that low-frequency stimulation of VOP enhances both facial and upper limb motor function. By identifying optimal stimulation target locations and parameters, this study contributes to refining DBS therapy for individuals with post-stroke and TBI-related motor impairments.