Probing peripheral neural pathways in electrically stimulation induced sensation

Abstract

Electrical stimulation of peripheral nerves can elicit sensations in the residual and missing limbs of amputees. The goal of this study is to determine how electrical stimulation activates peripheral neural pathways by examining the relationship between elicited sensations and activation of residual muscles proximal to the amputation. In this study, high-density (16-contact) composite flat interface nerve electrodes were implanted on the sciatic and tibial nerves above the knee of a participant with a trans-tibial amputation. The sensations elicited by applying stimulating pulses to selected contacts within the electrodes were classified into three categories: tactile sensation in the residual limb, tactile sensation in the missing limb, and feeling of muscle contraction in the residual limb. Surface electromyograms (EMG) were recorded from below-knee muscles in the residual limb prior to and during stimulation. Initial results suggest direct peripheral afferent activation induces tactile sensation in the participant’s missing limb. No significant elevated EMG was observed in any of the below-knee muscles when the subject perceived tactile sensation in his missing limb. However, EMG activity was observed in at least one of the muscles when he perceived tactile sensation in his residual limb. Sensations of muscle contractions coincided with a much higher EMG activity in all residual muscles. Our findings suggest that elicited tactile sensations in the missing limb are largely due to direct activation of afferent fibers. However, muscle contraction sensation in the residual limb may result from afferent activation by muscle recruitment.