Comparison between Invasive and Non-Invasive Synergistic Interactions of Brain and Spinal Stimulation and Novel Methods of Assessment

ABSTRACT

Spinal cord stimulation (SCS), applied epidurally (eSCS) or transcutaneously (tSCS) has demonstrated potential in movement disorders. However, direct comparisons between these modalities remain limited. This study integrated the two modalities with brain stimulation—a combination that has shown promise for neuromodulation in rats.To enhance rigor, we developed a framework for examining muscle activation in the form of motor-evoked-potential (MEP) recruitment curves, which are key for mapping and evaluating the effectiveness of neuromodulation techniques.

This study involved two groups that received cervical spinal cord stimulation combined with brain stimulation. The first group consisted of individuals undergoing cervical spine decompression surgery, in whom eSCS was applied. The second group included SCI and uninjured participants, in whom tSCS was applied. The timing of SCS was varied relative to brain stimulation to identify optimal convergence. MEPs in response to stimulation were analyzed. Accuracy and statistical power of the developed hierarchical Bayesian framework were assessed in simulations as well as in empirically observed data. Pairing brain stimulation with SCS consistently elicited larger MEPs than the sum of responses from individual modalities. The facilitation of paired stimulation was an order of magnitude greater with eSCS compared to tSCS.

The Bayesian framework provided robust parameter estimates and detected parameter shifts with fewer participants than current methods.

Lower facilitation observed with tSCS compared to eSCS may reflect less selective targeting of neural structures and underscores the potential of combined neurostimulation techniques. The Bayesian method represents a powerful computational tool for resource-constrained experiments, which will be embedded in a closed-loop framework in future work.

BIOGRAPHY

James McIntosh is an Associate Research Scientist in the Movement Recovery Laboratory at Columbia University. His work has centered on brain and spinal cord recording and neurostimulation, and the development of engineering and analytical tools to enable this research.