Peripheral nerve stimulation for tactile and proprioceptive feedback with phantom limb pain suppression in amputees
Authors: Soghoyan Gurgen , Biktimirov Artur , Matvienko Yury , Chekh Ilya , Sintsov Mikhail , Lebedev Mikhail 
Published: October 2022

Limb amputation causes multiple disabilities, including phantom limb pain (PLP). While motor functions could be restored to amputees with prostheses of different complexity, recreation of tactile sensation remains a challenging task. Peripheral nerve stimulation (PNS) performed transcutaneously or with implanted electrodes is a promising approach to enabling tactile and proprioceptive sensations. Additionally, PNS has a capacity of reducing PLP, particularly when it is enacted as tactile feedback in active exploration tasks. Since effective ways are not sufficiently developed for using PNS to simultaneously treat PLP and produce artificial tactile sensations, we conducted a study where upper-limb amputees were implanted with stimulating electrodes, and PNS was applied passively or during haptic tasks.In two bilateral transradial amputees were implanted for two weeks with stimulating electrodes placed in proximity to the medial, ulnar and radial nerves. The patient reported the state of their PLP and responsiveness to PNS in a journal, which they filled every day. Treatment with PNS started with a mapping session, where patients described their sensations caused by stimulation and referred them to the upper-limb phantom. During the mapping, PNS frequency, pulse width and amplitude were adjusted to achieve the most natural sensations. Next, in one patient, a series of sensorimotor tests were conducted , where the patient grasped objects of different sizes with a prosthetic hand while PNS provided proprioceptive feedback. Furthermore, both patients performed an active exploration task where they scanned a computer tablet with a stylus, received PNS-based feedback and thus determined the shape of invisible objects.The mapping study showed that PNS led to a range of sensation that could be referred to the phantom limb, including sensations resembling touch and proprioception. Moreover, in both patients, PNS reduced PLP even when applied passively. In one patient, PLP was abolished completely whereas the second patient reported a 70% reduction in the PLP. In addition to this clear therapeutic effect, PNS proved to be an effective tool to provide somatosensory feedback. One subject learned to discriminate the size of three objects with an accuracy of 78% by grasping an object with a bionic hand while PNS provided the feedback of the hand aperture, and both subjects learned the active scanning task. Finally, we compared the effects of transcutaneous electrical nerve stimulation (TENS) and PNS and found that patients can rely on sensory feedback of any kind during active exploration tasks. This two-week study in two amputees with peripheral-nerve implants showed that PNS could be effectively used for two purposes: suppressing PLP and providing prosthetic somatosensation during active exploration tasks. As such, this approach should be developed further using fully-implantable PNS systems that could be used long-term. Yet, given the comparable results obtained with TENS, noninvasive solutions could be effective in some patients for the same purpose of simultaneously suppressing PLP and generating prosthetic sensations.