Somatosensory burst peripheral nerve stimulation focally upregulates corticospinal and spinal excitability in the upper limb

Peripheral nerve stimulation (PNS) is commonly used in research and clinical settings for pain management and for augmenting somatosensory input for motor recovery. Its functional effects are dependent on stimulation parameters such as frequency, intensity, and duration of stimulation. Recently, interest in temporally modulated PNS (burst PNS), in which high-frequency carrier pulses are demodulated to low-frequency bursts, has increased. Burst PNS applied below the motor threshold (sensory) has been used to suppress pain and tremor. However, the effects of burst sensory PNS (sPNS) on corticospinal and spinal excitability are unknown, limiting its application. We evaluated the impact of a session of burst sPNS on corticospinal excitability through motor-evoked potentials (MEPs) and spinal excitability through F-wave and H-reflex assessments targeting the first dorsal interosseous (FDI) and flexor carpi radialis (FCR) muscles. Ten healthy participants underwent a randomized crossover study with two experimental visits, in which corticospinal and spinal excitability were evaluated before and after a session (40 min) of burst sPNS at the wrist or no stimulation (control). Compared with the control condition, burst sPNS resulted in a focal increase in MEP amplitudes (p < 0.001) in the FDI muscle, but not in the FCR muscle (p = 0.26). Similarly, only the F-wave amplitude increased following burst sPNS (p = 0.008) for the FDI muscle compared to the control condition, but no differences were observed in the H-reflex amplitude (p = 0.33) in the FCR muscle between the burst sPNS and the control condition. Our findings suggest that burst sPNS modulates spinal and corticospinal excitability in the short term (5–10 min in this study). However, the relative changes in cortical and spinal levels due to burst sPNS are unknown, and the timeline for these continued aftereffects requires further investigation.