Redirection of cutaneous sensation from the hand to the chest skin of human amputees with targeted reinnervation

Abstract

Amputees cannot feel what they touch with their artificial hands, which severely limits usefulness of those hands. We have developed a technique that transfers remaining arm nerves to residual chest muscles after an amputation. This technique allows some sensory nerves from the amputated limb to reinnervate overlying chest skin. When this reinnervated skin is touched, the amputees perceive that they are being touched on their missing limb. We found that touch thresholds of the reinnervated chest skin fall within near-normal ranges, indicating the regeneration of largefiber afferents. The perceptual identity of the limb and chest was maintained separately even though they shared a common skin surface. A cutaneous expression of proprioception also occurred in one reinnervated individual. Experiments with peltier temperature probes and surface electrical stimulation of the reinnervated skin indicate the regeneration of small diameter temperature and pain afferents. The perception of an amputated limb arising from stimulation of reinnervated chest skin may allow useful sensory feedback from prosthetic devices and provides insight into the mechanisms of neural plasticity and peripheral regeneration in humans.regeneration ͉ neural machine interface ͉ touch ͉ artificial limbs T he loss of an arm is a singularly debilitating injury. Improving the function of artificial arms remains a considerable challenge, especially for high-level amputations where the disability is greatest. A primary impediment to better function is that current prostheses provide very little sensory feedback. The amputees must rely primarily on vision to manipulate objects, and they cannot feel what they touch with motorized prosthetic hands. This limitation greatly increases the cognitive burden on the amputee and impedes the use of the artificial limb.We have developed a neural-machine interface called targeted reinnervation (TR) that provides enhanced motor control and the potential for meaningful sensation feedback for artificial arms (1-3). The amputated brachial plexus nerves that once provided motor control and sensory feedback in the missing limb are transferred to arm and chest muscles that remain after the amputation. Once reinnervated, these muscles produce electromyogram (EMG) signals that correspond to the original arm control signals sent from the brain down the brachial plexus nerves. This process provides improved and more intuitive control of a motorized artificial arm (4-6). The contractions of the reinnervated muscles function as biological amplifiers for the motor commands transmitted by the amputated arm nerves. Concurrently, the sensory nerve fibers in these amputated nerves appear to reinnervate the skin overlying the target muscles. When this reinnervated skin is touched, the amputee feels as if the missing hand is being touched. This skin reinnervation may provide a direct portal to the sensory pathways of the amputated arm and hand. It could potentially provide an amputee with the ability to feel what he touches with a pro...

Re-emergence of hand-muscle representations in human motor cortex after hand allograft

“…However, fMRI results indicate that the restoration of afferent input (albeit incomplete) leads to activation in the region corresponding to the hand representation in S1 (14,32,33). Likewise, results gathered in patient CD (34) and in upper-limb amputees whose arm nerves were redirected to chest muscles (35) indicate that peripheral and central pathways remain viable even after prolonged periods of amputation-induced disuse, and that somatosensory circuits of the human brain readily reintegrate peripheral information pending its availability.…”

Prosthetic Myoelectric Control Strategies: A Clinical Perspective

“…5), this landmark procedure allowed the patient to perform simultaneous control of two degrees of freedom at the elbow and wrist of a prosthetic arm, using standard reconstructive techniques and without the need for implantable devices [70]. TMR has since developed, incorporating more patients [71,72], and also describing the transfer of hand sensation to the area where nerves have been re-directed [73]. Notably, this technique has not only allowed multifunctional control of prosthetic limbs in realtime [74] but has also acted as a catalyst for further development into EMG processing for prosthetic control.…”

“…TMR has demonstrated that not only were motor nerves transferred to new muscles but also some sensory nerves. In a shoulder disarticulation patient's reinnervated regions, tactile stimuli gave the sensation of being touched on the missing limb, while still being able to differentiate hand from chest sensation [73]. In addition, using a haptic device, which transmitted vibration from the prosthetic limb to the amputee's reinnervated skin, encouraged the patient to include the prosthesis as part of his self-image, as opposed to a foreign entity [79].…”

Neuroprosthetics: Once more, with feeling

“…It turned out that the re-routed nerves had grown into the chest skin, and his brain was interpreting the sensory signals as coming from his hand. Some parts of his chest felt like his palm, whereas others felt like his fingers or forearm 7 .…”