Biomimetic Intraneural Sensory Feedback Enhances Sensation Naturalness, Tactile Sensitivity, and Manual Dexterity in a Bidirectional Prosthesis

Peripheral intraneural stimulation can provide tactile information to amputees. However, efforts are still necessary to identify encoding strategy eliciting percepts that are felt as both natural and effective for prosthesis control. Here we compared the naturalness and efficacy of different encoding strategies to deliver neural stimulation to trans-radial amputees implanted with intraneural electrodes. Biomimetic frequency modulation was perceived as more natural, while amplitude modulation enabled better performance in tasks requiring fine identification of the applied force. Notably, the optimal combination of naturalness and sensitivity of the tactile feedback can be achieved with "hybrid" encoding strategies based on simultaneous biomimetic frequency and amplitude neuromodulation. These strategies improved the gross manual dexterity of the subjects during functional task while maintaining high levels of manual accuracy. They also improved prosthesis embodiment, reducing abnormal phantom limb perceptions ("telescoping effect"). Hybrid strategies are able to provide highly sensitive and natural percepts and should be preferred.