Non-invasive magnetic peripheral nerve stimulation: Sensitivity and specificity for evoked autonomic and kinematic responses

Neuromodulation via invasive nerve stimulation has been used as an adjuvant to physical rehab in targeted plasticity therapy for neural injuries, and as a therapeutic intervention for clinical conditions, including depression. However, surgeries for implantation of stimulation devices carry general limitations of cost and surgical risk. To overcome these shortcomings, we have been assessing the effectiveness of noninvasive alternatives for nerve stimulation. The primary goal of this study was to test the hypothesis that noninvasive magnetic peripheral nerve stimulation (mPNS) of the median nerve, a mixed peripheral nerve, in healthy adult males and females with a figure-8 coil is sensitive to induce bilateral peripheral autonomic and cardiovascular responses comparable to those evoked by electrocutaneous peripheral nerve stimulation (ePNS). To test this hypothesis, we applied to the right median nerve of healthy subjects a single pulse of an electrocutaneous stimulus (30-mA, 200-µs cathodal pulse) or a magnetic stimulus delivered by a 70-mm coil in one of four 90° orientations about a symmetric axis of rotation (perpendicular to the xy-plane of the coil) centered ~8 cm proximal to the radial styloid process. Bilateral peripheral vasomotor and sudomotor responses were recorded by photoplethysmography (BioPac) and electrodermal activity sensors (Plux Biosignals), respectively. Hemodynamic metrics of heart rate, blood pressure, and mean arterial pressure were recorded by a VitalStreams system (Caretaker Medical) and lead-II electrocardiogram (BioPac). The mPNS specificity was assessed using videos of hand kinematics recorded during a short train of stimuli (30 Hz for 0.1s) delivered to the median, ulnar, or radial nerves. Sensation and perceived movement were assessed using a visual analog scale (VAS), with equidistant integer rating bubbles across a 100-mm line ranging from -5 (full extension) to +5 (full flexion) for movement and 0 (no startle/pain) to 10 (severe startle/pain) for discomfort. Data were statistically analyzed using a repeated-measures design or a non-parametric equivalent with post-hoc correction and alpha level of 0.05. Results indicated that: (i) the magnitude of mPNS-induced peripheral sudomotor, vasomotor, and hand kinematic responses depended on coil orientation [p < 0.05], (ii) the magnitude and latency of mPNS-induced peripheral autonomic and vasomotor responses were comparable to those elicited by ePNS [p = 0.593], and (iii) for comparable field intensity and region of interest, mPNS was less noxious than ePNS [p < 0.01]. Kinematic data also revealed that mPNS specifically activated muscle groups innervated by the targeted nerve, as stimulation over the median nerve induced flexion of metacarpophalangeal (MCP) joints 1-3 whereas stimulation over the ulnar or radial nerves induced flexion of MCP joints 4-5 and extension of MCP joints 1-5, respectively [p < 0.05]. These findings show selectivity and effectiveness of magnetic stimulation of peripheral nerves and, thereby, strongly support mPNS as a viable noninvasive alternative for therapeutic neuromodulation. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.