Evaluation of multiple perceptual qualities of transcutaneous electrical nerve stimulation for evoked tactile sensation in forearm amputees

Abstract

Objective: Evoked tactile sensation (ETS) elicited by transcutaneous electrical nerve stimulation (TENS) is promising to convey digit-specific sensory information to amputees naturally and non-invasively. Fitting ETS-based sensory feedback to amputees entails customizing coding of multiple sensory information for each stimulation site. This study was to elucidate the consistency of percepts and qualities by TENS at multiple stimulation sites in amputees retaining ETS. Approach: Five transradial amputees with ETS and fourteen able-bodied subjects participated in this study. Surface electrodes with small size (10 mm in diameter) were adopted to fit the restricted projected finger map on the forearm stump of amputees. Effects of stimulus frequency on sensory types were assessed, and the map of perceptual threshold for each sensation was characterized. Sensitivity for vibration and buzz sensations was measured using distinguishable difference in stimulus pulse width. Rapid assessments for modulation ranges of pulse width at fixed amplitude and frequency were developed for coding sensory information. Buzz sensation was demonstrated for location discrimination relating to prosthetic fingers. Main results: Vibration and buzz sensations were consistently evoked at 20 Hz and 50 Hz as dominant sensation types in all amputees and able-bodied subjects. Perceptual thresholds of different sensations followed a similar strength-duration curve relating stimulus amplitude to pulse width. The averaged distinguishable difference in pulse width was 12.84 ± 7.23 μs for vibration and 15.21 ± 6.47 μs for buzz in able-bodied subjects, and 14.91 ± 10.54 μs for vibration and 11.30 ± 3.42 μs for buzz in amputees. Buzz coding strategy enabled five amputees to discriminate contact of individual fingers with an overall accuracy of 77.85%. Significance: The consistency in perceptual qualities of dominant sensations can be exploited for coding multi-modality sensory feedback. A fast protocol of sensory coding is possible for fitting ETS-based, non-invasive sensory feedback to amputees.

EEG Features of Evoked Tactile Sensation: Two Cases Study

“…The types of stimulation could be mechanical stimulation or TENS. Furthermore, studies have indicated that amputees can feel a more natural and richer tactile sensation under TENS than under mechanical stimulation (Mulvey et al, 2012 ; Zhang et al, 2022 ).…”

Study of Tactile Sensation Somatotopy and Homology Between Projected Fingers in Residual Limb and Natural Fingers in Intact Limb

“…Second, considering the type of restoration, the artificial interface could have two types, sensory rebuild [15]- [18], [21] and sensory substitution [22], [23]. Compared to the sensory substitution that is building a new sensory stream to the brain and needs the users to learn via days of training [26], the sensory rebuild is trying to connect the tactile stimulation via the residual nerve pathway, where thus sensory rebuild is a natural way to be able to deliver more kinds of tactile sensations intuitively without learning [3], [27].…”

“…By considering the application potential for practical prosthetic hands, we are focusing on the techniques that can combine the non-invasive and sensory rebuild. Among noninvasive interface and sensory rebuild technologies, projected finger mapping (PFM) combined with TENS is capable of building a stable sensory interactive interface of tactile sensations of the lost hand [21], [27], [28]. The PFM is located in the skin of the distal of the forearm stump, and can evoke the tactile sensation of the missing fingers while different parts of the PFM are stimulated by mechanical or electrical stimuli.…”

“…In the homology aspect, the stimuli on the projected finger will intuitively evoke a similar sensation for the corresponding phantom finger. By encoding the electrical stimulation parameters, the projected finger can evoke the phantom finger to generate sensation patterns such as touch, buzz, vibration, numbness, and tingling [27], [30].…”

“…In , the results also showed that the activation region evoked by the projected finger was mirror symmetric with the activation region of the contralateral healthy finger in the sensory cortex. Research by [27] revealed that ETS has psychophysical characteristics of various perceptual elements and provided the feasibility to realize multimodal perceptual information coding via using ETS.…”