Advancing Neuromodulation Modality for Stroke: Deep Brain Stimulation of the Motor Thalamus for Speech and Swallowing Restoration

Introduction: Stroke frequently results in facial motor impairments, manifesting as paresis, dysphagia, and dysarthria, which pose significant risks of suffocation and social isolation. Deep brain stimulation (DBS) can target intrinsic pathways to modulate the activity of vital cortical areas and downstream neural transmission. One structure of interest is the ventro-oralis posterior/ventro-oralis anterior (VOP/VOA) of the motor thalamus. The VOP/VOA contains excitatory projections to the primary motor cortex (M1) that can be potentiated using DBS to facilitate facial and oropharyngeal motor function after stroke. We hypothesized that VOP/VOA stimulation increases M1 excitability, enhances corticobulbar motor output, and restores volitional control of facial and oropharyngeal muscles, thereby improving speech and swallowing in stroke survivors.

Methods: VOP/VOA stimulation was acutely performed in ten patients with intact corticobulbar pathways undergoing implantation of either DBS electrodes for essential tremor (n=7) or stereoelectroencephalography (SEEG) electrodes for epilepsy (n=3). Intraoperatively, a macroelectrode array was placed over M1 for direct cortical stimulation (DCS) paired with VOP/VOA stimulation. Facial motor-evoked potentials (MEPs) and articulation tasks were recorded to assess facial motor function. Additionally, two patients with corticobulbar lesions, resulting in facial paresis, dysarthria, and dysphagia, were implanted with permanent DBS in the VOP/VOA. Facial articulation tasks, videofluoroscopic swallow studies, and speech intelligibility assessments were conducted with and without DBS.

Results: In patients with intact corticobulbar pathways, VOP/VOA stimulation significantly amplified facial MEPs and enhanced the range and speed of orofacial movements. In patients with lesioned corticobulbar tracts, VOP/VOA stimulation restored volitional facial movements. Importantly, DBS of the VOP/VOA improved control of respiratory, phonatory, resonatory, and articulatory functions, resulting in clinically significant improvements in speech intelligibility and swallowing.

Conclusion : This study demonstrated that deep brain stimulation of the motor thalamus potentiates facial and oropharyngeal motor output to produce functional improvements in facial movement, swallowing, and speech in humans with cerebral lesions. These outcomes support DBS of the motor thalamus as a novel therapeutic approach to treat post-stroke facial paresis, dysphagia, and dysarthria.