A closed-loop hand prosthesis with simultaneous intraneural tactile and position feedback

Current myoelectric prostheses allow transradial amputees to regain voluntary motor control of their artificial limbby exploiting residual muscle function in the forearm. However, the overreliance on visual cues resulting from alack of sensory feedback is a common complaint. Recently, several groups have provided tactile feedback in upperlimb amputees using implanted electrodes, surface nerve stimulation, or sensory substitution. These approacheshave led to improved function and prosthesis embodiment. Nevertheless, the provided information remainslimited to a subset of the rich sensory cues available to healthy individuals. More specifically, proprioception,the sense of limb position and movement, is predominantly absent from current systems. Here, we show that sen-sory substitution based on intraneural stimulation can deliver position feedback in real time and in conjunctionwith somatotopic tactile feedback. This approach allowed two transradial amputees to regain high and close-to-natural remapped proprioceptive acuity, with a median joint angle reproduction precision of 9.1° and a medianthreshold to detection of passive movements of 9.5°, which was comparable with results obtained in healthy par-ticipants. The simultaneous delivery of position information and somatotopic tactile feedback allowed both am-putees to discriminate the size and compliance of four objects with high levels of performance (75.5%). Theseresults demonstrate that tactile information delivered via somatotopic neural stimulation and position informationdelivered via sensory substitution can be exploited simultaneously and efficiently by transradial amputees. Thisstudy paves a way to more sophisticated bidirectional bionic limbs conveying richer, multimodal sensations