Abstract
BackgroundElectrical stimulation of residual afferent nerve fibers can evoke sensations from a missing limb after amputation, and bionic arms endowed with artificial sensory feedback have been shown to confer functional and psychological benefits. Here we explore the extent to which artificial sensations can be discriminated based on location, quality, and intensity.MethodsWe implanted Utah Slanted Electrode Arrays (USEAs) in the arm nerves of three transradial amputees and delivered electrical stimulation via different electrodes and frequencies to produce sensations on the missing hand with various locations, qualities, and intensities. Participants performed blind discrimination trials to discriminate among these artificial sensations.ResultsParticipants successfully discriminated cutaneous and proprioceptive sensations ranging in location, quality and intensity. Performance was significantly greater than chance for all discrimination tasks, including discrimination among up to ten different cutaneous location-intensity combinations (15/30 successes, p < 0.0001) and seven different proprioceptive location-intensity combinations (21/40 successes, p < 0.0001). Variations in the site of stimulation within the nerve, via electrode selection, enabled discrimination among up to five locations and qualities (35/35 successes, p < 0.0001). Variations in the stimulation frequency enabled discrimination among four different intensities at the same location (13/20 successes, p < 0.0005). One participant also discriminated among individual stimulation of two different USEA electrodes, simultaneous stimulation on both electrodes, and interleaved stimulation on both electrodes (20/24 successes, p < 0.0001).ConclusionElectrode location, stimulation frequency, and stimulation pattern can be modulated to evoke functionally discriminable sensations with a range of locations, qualities, and intensities. This rich source of artificial sensory feedback may enhance functional performance and embodiment of bionic arms endowed with a sense of touch.
Highlights
Electrical stimulation of residual afferent nerve fibers can evoke sensations from a missing limb after amputation, and bionic arms endowed with artificial sensory feedback have been shown to confer functional and psychological benefits
Asterisks overlaid on the confusion matrix indicate statistical significance with regards to an individual condition. a Subject S3 successfully discriminated among percepts evoked via individual stimulation of four different ulnar-nerve-Utah slanted electrode array (USEA) electrodes, as well as simultaneous stimulation of all four electrodes. b Subject S3 discriminated successfully between individual stimulation of two ulnar-nerve-USEA electrodes, as well as simultaneous interleaved stimulation and interleaved stimulation of the same two ulnar-nerve-USEA electrodes
Timing of individual stimulation pulses is shown as a raster plot to the left of the hand. c Subject S4 discriminated among eight different stimulation configurations: individual stimulation of each of three ulnar-nerve-USEA electrodes, simultaneous combined stimulation using different subsets of two of these three electrodes, simultaneous combined stimulation using all three electrodes, and no stimulation (11/24 correct trials, p < 0.0001, binomial test)
Summary
Electrical stimulation of residual afferent nerve fibers can evoke sensations from a missing limb after amputation, and bionic arms endowed with artificial sensory feedback have been shown to confer functional and psychological benefits. Peripheral-nerve interface approaches, such as Utah Slanted Electrode Arrays (USEAs) [3, 4, 11,12,13,14,15], cuff electrodes [16, 17], transverse intrafascicular multichannel electrodes [1, 18,19,20,21,22], flat interface nerve electrodes [23,24,25,26], and longitudinal intrafascicular electrodes [27,28,29,30] have demonstrated the ability to evoke sensory percepts at different locations, and of different qualities (e.g., submodalities) and intensities on the missing hand of amputees These sensory percepts have been shown to be important for identifying objects of different shapes/ sizes and compliances during closed-loop prosthesis control [1, 4, 11, 29, 31,32,33]. Reports on the discriminability of USEA-evoked percepts have been limited to a small number of percepts [11], despite the fact that USEAs can evoke numerous sensory percepts [4, 13]
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