Somatosensory Evoked Potentials following upper limb noninvasive electrical stimulation: a case study.

Abstract

Lack of sensory feedback is one of the main issues contributing to lack of control and embodiment for upper-limb prostheses. Noninvasive nerve stimulation may help amputees overcome such limitations by providing a degree of somatotopic feedback, however its neural correlates have been only partly characterized so far. While the effects of median nerve stimulation have been studied, little attention has been given to ulnar nerve and bipolar stimulation, which might provide a finer modulation of the somatotopic sensation. Here, monopolar and bipolar transcutaneous electrical nerve stimulation (TENS) is repeatedly applied to the ulnar and median nerves and elicited Somatosensory Evoked Potentials (SEPs) are characterized by means of electroencephalography (EEG). Clear P50, P150 and P270 SEPs were outlined, with significantly different amplitudes between configurations. In each case scalp topographies showed a strong contralateral activation in the early phase after the stimulus onset (40-100 ms), compatible with generators in the somatosensory cortex and in accordance to previous literature on actual tactile stimuli, which gives way to a frontal-central distribution at long latencies (130-190 ms). These findings, although needing further validation with a larger pool of subjects, show that bipolar TENS could have potential applications in improving prosthesis control with tactile feedback.