Restoration of Natural Somatic Sensations to the Amputees: Finding the Right Combination of Neurostimulation Methods

Abstract

Limb amputation results in such devastating consequences as loss of motor and sensory functions and phantom limb pain (PLP). Here we explored peripheral nerve stimulation (PNS), spinal cord stimulation (SCS) and transcutaneous electrical nerve stimulation (TENS) as the approaches to enable tactile and proprioceptive sensations in amputees, and suppress PLP. We investigated the efficacy of these approaches for sensory discrimination tasks, namely determining object size and softness using a bionic prosthesis of the hand. Two transhumeral amputees were implanted for four weeks with stimulating electrodes placed in the medial nerve and/or epidurally over the spinal cord. Both PNS and SCS mapped to the sensation in different parts of the phantom hand, which was confirmed by both subjective reports and electroencephalographic (EEG) recordings of cortical responses to stimulation. Surprisingly, PNS provided more naturalistic sensations compared to SNS. Moreover, these sensations were felt as emerging from the prosthetic hand when the participants performed sensorimotor tasks where they determined the size and softness of objects being grasped. As they practiced in these tasks, the prosthetic sensations became more natural. While the participants could perform some of the tasks, for example tactile surface exploration, using auditory feedback, PNS and/or SCS have a benefit of better approximating the sensations lost to the amputation while suppressing PLP.