Neural Engineering Seminar
Speaker: Ben Alexander
Advisors: Profs. Bolu Ajiboye, Robert Kirsch
Title: Electromyographic Characterization of C-FINEs for Upper Extremity FES
Abstract: The Reconnecting the Hand and Arm to the Brain (ReHAB) clinical trial combines Composite Flat Interface Nerve Electrodes (C-FINEs) around the nerves of the upper extremity with intracortical microelectrodes in the sensory and motor areas of the brain in order to create a bidirectional motor and sensory neuroprosthesis. The system enables those with tetraplegia due to high level spinal cord injuries to volitionally control their paralyzed upper extremity via functional electrical stimulation (FES). However, with 90 stimulatable contacts and many different tunable stimulation parameters, the creation of functional stimulation patterns currently requires significant time investment from an expert with many years of experience. In the short term, characterizing the muscle activation properties of the C-FINEs in the human upper extremity provides quantitative data that can inform the manual creation of stimulation patterns. In future work, we hope to determine how stimulation parameters can be automatically constructed or tuned using these new datasets.
In this work, we evaluated the recruitment properties of 16-contact C-FINEs implanted around 6 nerves innervating the right upper extremity of a human participant with a high-cervical spinal cord injury (AIS-B C3/C4). We quantified muscle activation as the rectified and integrated electromyographic (EMG) response in the first 40ms after a twitch activation of given pulsewidth (PW) and pulse amplitude (PA). We used this method to acquire PW modulated recruitment curves (RCs) for all 90 stimulatable contacts at multiple amplitudes. These data were then summarized by creating threshold plots that present the amount of charge required to bring each muscle to a 20% activation threshold as a function of position of the contacts on the cuff. The raw RCs and the threshold plots provide information about the selectivity and functionality of the cuffs. We found cuff-wide trends in activation thresholds that may indicate the spatial positioning of each nerve within its respective cuff and muscle-specific trends that suggest relationships between cuff position, nerve branch points, and selectivity and may inform the ideal placement of future cuffs for upper extremity FES. This increased knowledge of C-FINEs’ muscle recruitment properties in the upper extremity sets the foundation for future development of stimulation patterns for complex upper extremity movements in the future.