Sensitivity to temporal parameters of intraneural tactile sensory feedback

Abstract

Background: Recent studies have shown that neural stimulation can be used to provide artificial sensory feedback to amputees eliciting sensations referred on the amputated hand. The temporal properties of the neural stimulation modulate aspects of evoked sensations that can be exploited in a bidirectional hand prosthesis. Methods: We previously collected evidence that the derivative of the amplitude of the stimulation (intra-digit temporal dynamics) allows subjects to recognize object compliance and that the time delay among stimuli injected through electrodes implanted in different nerves (inter-digit temporal distance) allows to recognize object shapes. Nevertheless, a detailed characterization of the subjects' sensitivity to variations of intra-digit temporal dynamic and inter-digit temporal distance of the intraneural tactile feedback has not been executed. An exhaustive understanding of the overall potentials and limits of intraneural stimulation to deliver sensory feedback is of paramount importance to bring this approach closer and closer to the natural situation. To this aim, here we asked two trans-radial amputees to identify stimuli with different temporal characteristics delivered to the same active site (intra-digit temporal Dynamic Recognition (DR)) or between two active sites (inter-digit Temporal distance Recognition (TR)). Finally, we compared the results achieved for (simulated) TR with conceptually similar experiments with real objects with one subject. Results: We found that the subjects were able to identify stimuli with temporal differences (perceptual thresholds) larger than 0.25 s for DR and larger than 0.125 s for TR, respectively. Moreover, we also found no statistically significant differences when the subjects were asked to identify three objects during simulated 'open-loop' TR experiments or real 'closed-loop' tests while controlling robotic hand. Conclusions: This study is a new step towards a more detailed analysis of the overall potentials and limits of intraneural sensory feedback. A full characterization is necessary to develop more advanced prostheses capable of restoring all lost functions and of being perceived more as a natural limb by users.

A Psychometric Platform to Collect Somatosensory Sensations for Neuroprosthetic Use

“…The intensity was used to find the perceptual thresholds for each stimulation channel ( 4 , 23 , 24 , 31 ), together with the range of stimulation (between threshold and below pain level). Using a VAS scale in the range from 0 to 10 also enables us to identify perceptual magnitude levels ( 5 , 23 , 32 , 52 , 62 ).…”

“…To describe the quality of sensations, we used a scale presented by Lenz et al (34) and used also by Valle et al (9). For the sensation type, we adapted the questionnaire proposed by Kim et al (36) based on our experience with several upper limb patients stimulated with invasive (4,9,23,24,29,31,(40)(41)(42)(43)(44)(45)(46)(47) and non-invasive technologies (17,48). We also considered other studies on sensations elicited using peripheral (5,10,14,22,(49)(50)(51)(52)(53)(54)(55) or central (6,8,13) neural stimulation approaches.…”

“…The external stimulation of the residual (still functional proximal to the lesion) nervous structures guarantees to evoke an artificial sensation that can also be controlled by modulating the stimulation parameters (22)(23)(24).…”

Peripheral neurostimulation for encoding artificial somatosensations

“…The modulation of the spatiotemporal parameters of the neural stimulation allows to also encode some aspects of more complex features related to the external stimulus, such as its texture (Mazzoni et al, 2020; Oddo et al, 2016), stiffness (Schiefer et al, 2018; Valle, Strauss, et al, 2020) (Figure 2b) or shape (Raspopovic et al, 2014; Valle, Petrini, et al, 2018). It has been achieved exploiting the intradigit temporal dynamics and interdigit temporal distance of the neural stimulation.…”

“…(b) Two encoding schemes to provide the user with information regarding the shape or compliance of the grasped object. The variations of intradigit temporal dynamics or interdigits temporal distance have been proposed as possible approaches to encode these object properties (adapted from Valle, Strauss, et al, 2020).…”