Efficacy of a Gaussian-frequency charge-imbalanced biphasic waveform for facilitating swallowing via thoracic epidural spinal cord stimulation.

Thoracic spinal cord stimulation (SCS) has been reported to facilitate swallowing, however the underlying brainstem mechanisms remain unclear. We developed a Gaussian-frequency, charge-imbalanced biphasic waveform designed to enhance sensory afferent drive to spinal circuits while maintaining safe charge delivery. Using an in situ perfused brainstem-spinal cord preparation of rats, which preserves intrinsic swallowing circuits and enables direct assessment of central pattern generator (CPG) outputs, we compared this waveform with a conventional fixed-frequency monophasic pulse used in clinical and experimental settings. Electrical stimulation was applied epidurally to the T8 spinal segment via a concentric electrode, and neural activity was recorded from the phrenic nerves, vagus nerves, and hypoglossal nerves under three conditions: no stimulation, monophasic stimulation, and Gaussian-frequency charge-imbalanced biphasic stimulation. Both stimulation types significantly increased swallow count, shortened the swallowing interburst interval, and enhanced swallow-related vagus nerve activity (VNA) and hypoglossal nerve activity (HNA) compared with no stimulation. However, the Gaussian-frequency waveform produced a significantly greater increase in swallow number than monophasic stimulation. Consistent with previous findings that stochastic stimulation can reduce sensory adaptation and improve detection of weak inputs, our results suggest that, once the swallowing CPG is engaged, stochastic stimulation does not primarily accelerate its rhythm but instead increases the likelihood and duration of CPG activation bouts.Thoracic SCS using this waveform may therefore provide a neuromodulatory strategy that may enhance the functional selectivity of cathodal activation within spinal circuits within spinal circuits and facilitates recruitment of brainstem swallowing networks.