Peripheral magnetic stimulation of the upper-limb nerves: evoked sensations, phantom-pain relief, and cortical responses

Peripheral magnetic stimulation (PMS) is a noninvasive technique applicable to post-stroke rehabilitation, treatment of phantom limb pain (PLP) and generating neuroprosthetic sensations. Here we aimed to test whether PMS could be utilized to enable sensory feedback from hand prostheses and suppress PLP. Accordingly, we induced somatic sensations with PMS and conducted EEG measurements to assess sensory evoked potentials (SEPs) in 30 able-bodied participants (controls) and 11 individuals with transradial amputation. Single PMS pulses of varying amplitude were applied to the left arm locations overlying the median, radial, and ulnar nerves. Subjective accounts of sensations were collected using PerceptMapper, the University of Pittsburghs multitouch interface. After the best location for PMS was found, continuous stimulation (20 or 40 Hz, delivered in 5-min blocks with 5-7 min interblock intervals for patricipant breaks and EEG setup checks) was applied. The control participants reported experiencing sensations in their hands. The amputees felt sensations in their phantom hands. PMS evoked SEPs in both the controls and amputees. The analysis of intertrial coherence showed significant phase consistency of the stimulus-locked EEG responses across trials for the controls and amputees. The measurements of visual analogue scale (VAS) scale showed that PMS did not change PLP in 2 participants, increased it in 4, and decreased in 3. We propose that PMS could be used to assess the effects of peripheral nerve stimulation on somatic sensations, PLP and cortical activity prior to the surgical placement of electrode implants. Significance StatementPeople with amputation have two critical needs: (1) their prosthetic limbs being augmented with naturalistic somatic sensations, and (2) their PLP, which develops in the majority of cases, being suppressed. Electrical stimulation with peripheral nerve implants offers a solution for both needs, but invasiveness of this procedure poses a number of problems. Here we show that PMS offers a noninvasive tool for testing the effects of peripheral nerve stimulation before any invasive implants are placed. PMS causes somatic sensations, modulates PLP and evokes cortical responses evident in EEG recordings. These effects of PMS were documented in both healthy controls and amputees. The results suggest that PMS combined with EEG measurements could serve as tools for testing potential implantation sites.