Sensory Feedback in Upper Limb Prostheses

Loss of an arm is a devastating condition that can cross all socioeconomic groups. A major step forward in rehabilitation of amputees has been the development of myoelectric prostheses. Current robotic arms allow voluntary movements by using residual muscle contraction. However, a significant issue is lack of movement control and sensory feedback. These factors play an important role in integration and embodiment of a robotic arm. Without feedback, users rely on visual cues and experience overwhelming cognitive demand that results in poorer use of a prosthesis. The complexity of the afferent system presents a great challenge of creating a closed-loop hand prosthesis. Several groups have shown progress providing sensory feedback for upper limb amputees using robotic arms. Feedback, although still limited, is achieved through direct implantation of intraneural electrodes as well as through non-invasive methods. Moreover, evidence shows that over time some amputees develop a phantom sensation of the missing limb on their stump. This phenomenon can occur spontaneously as well as after non-invasive nerve stimulation, suggesting the possibility of recreating a sensory homunculus of the hand on the stump. Furthermore, virtual reality simulation in combination with mechanical stimulation of skin could augment the sensation phenomenon, leading to better interface between human and robotic arms.