Tapping Into the Language of Touch: Using Non-invasive Stimulation to Specify Tactile Afferent Firing Patterns

Abstract

The temporal pattern of action potentials can convey rich information in a variety of sensory systems. We describe a new non-invasive technique that enables precise, reliable generation of action potential patterns in tactile peripheral afferent neurons by brief taps on the skin. Using this technique, we demonstrate sophisticated coding of temporal information in the somatosensory system, that shows that perceived vibration frequency is not encoded in peripheral afferents as was expected by either their firing rate or the underlying periodicity of the stimulus. Instead, a burst gap or silent gap between trains of action potentials conveys frequency information. This opens the possibility of new encoding strategies that could be deployed to convey sensory information using mechanical or electrical stimulation in neural prostheses and brainmachine interfaces, and may extend to senses beyond artificial encoding of aspects of touch. We argue that a focus on appropriate use of effective temporal coding offers more prospects for rapid improvement in the function of these interfaces than attempts to scale-up existing devices.

Temporal patterns in electrical nerve stimulation: Burst gap code shapes tactile frequency perception

“…The benefit of the burst stimulation method we describe here is that we can control perceived frequency, which is determined by the burst gap, regardless of burst features such as the number of pulses within a burst [ 5 ]. Hence, in haptic devices and brain-machine interfaces, this coding strategy may provide a way to modulate frequency perception by means of changing the inter-burst interval and possibly other perceptual features of tactile stimuli encoded by spiking activity within individual bursts [ 58 ].…”

Multiplexing intensity and frequency sensations for artificial touch by modulating temporal features of electrical pulse trains

“…In conclusion, our strategy might enable expansion of the dynamic range for intensity modulation ( Sachs et al, 1980 ; Kaczmarek et al, 1992 ), which could potentially deliver a sharper spatial contrast between individual stimulation channels when rendering surface texture and object shape reliant on spatial intensity modulation, accompanied by independently controlled tactile frequency perception for mimicking surface interaction during exploratory movements. Accordingly, complex temporal patterns of burst stimulation offer the opportunity for improving information encoding via neural interfaces, which will open new opportunities for control of neuroprostheses in a rapidly developing field ( George et al, 2019 ; Bensmaia et al, 2020 ; Vickery et al, 2020 ).…”

“…One technology to generate such temporal spiking patterns in peripheral afferents is by very fast mechanical pulses with durations comparable to an action potential ( Birznieks et al, 2019 ). For broader application in neural prosthetics ( Vickery et al, 2020 ), we have verified experimentally that the same coding scheme can be implemented using electrocutaneous stimulation ( Ng et al, 2020 , 2021 ) and auditory click stimulation ( Sharma et al, 2022a , 2022b ).…”

Contribution of remote Pacinian corpuscles to flutter-range frequency discrimination in humans

“…Our group has previously developed pulsatile mechanical stimuli that break the confounding link between vibratory stimulus frequency and the afferent population recruited 20,21 . These pulsatile stimuli have a brief protraction time of ~2 ms, which is independent of the repetition rate (frequency), and generate a single spike per pulse in each activated afferent, as confirmed by microneurography 22,23 .…”