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

Peripheral intraneural stimulation can provide tactileinformation to amputees. However, efforts are stillnecessary to identify encoding strategy-elicitingpercepts that are felt as both natural and effectivefor prosthesis control. Here we compared the natu-ralness and efficacy of different encoding strategiesto deliver neural stimulation to trans-radial amputeesimplanted with intraneural electrodes. Biomimeticfrequency modulation was perceived as more natu-ral, while amplitude modulation enabled betterperformance in tasks requiring fine identification ofthe applied force. Notably, the optimal combinationof naturalness and sensitivity of the tactile feedbackcan be achieved with ‘‘hybrid’’ encoding strategiesbased on simultaneous biomimetic frequency andamplitude neuromodulation. These strategies im-proved the gross manual dexterity of the subjectsduring functional task while maintaining high levelsof manual accuracy. They also improved prosthesisembodiment, reducing abnormal phantom limb per-ceptions (‘‘telescoping effect’’). Hybrid strategiesare able to provide highly sensitive and natural per-cepts and should be preferred.