Over the last decade, there has been a remarkable increase in the number of clinical trials using electrical spinal cord stimulation to alleviate sensorimotor dysfunctions caused by traumatic spinal cord injury (SCI). Interestingly, despite using different stimulation modalities across studies, such as epidural stimulation (ES) or dorsal root ganglia stimulation (DRGS), similar motor outcomes have been achieved, and in turn, strengthened momentum to translate spinal stimulation as a robust clinical tool for SCI rehabilitation. To investigate how spinal stimulation affects motor outcomes, surface electromyography is used to assess muscle activity in response to specific stimulation parameters (e.g., frequency, amplitude) and contact configurations. We characterized lower extremity evoked responses produced by ES and DRGS in 19 clinical trial participants with traumatic SCI. Our results showed that at threshold intensity, ES demonstrated bias for activating distal muscles while DRGS preferentially activated proximal muscles ipsilateral to the stimulation electrode. Following paired stimulation pulses spaced 50 milliseconds apart, suppression of the second pulse response was observed in both modalities for all participants, while more pronounced suppression was observed with ES compared to DRGS. DRGS-evoked EMG response latencies were shorter compared to ES-evoked EMG response across proximal leg muscles. Altogether, these results demonstrate that ES and DRGS activate motoneurons projecting to lower extremity muscles through distinct yet overlapping mechanisms. These electrophysiological signatures are unique to each stimulation modality and may guide individually tailored therapies to improve task-specific lower extremity motor function.
Asp et al. (Fri,) studied this question.