Creation of virtual channels in the retina using synchronous and asynchronous stimulation—a modelling study

Abstract

Objective. The spatial resolution of an implantable neural stimulator can be improved by creation of virtual channels (VCs). VCs are commonly achieved through synchronized stimulation of multiple electrodes. It remains unknown whether asynchronous stimulation is able to generate comparable VC performance in retinal stimulation, and how VC can be optimized by re-designing stimulation settings. This study begins with exploring the feasibility of creating VCs using synchronous and asynchronous epiretinal stimulation, and ending with predicting the possible VC performance with a thorough exploration of stimulation parameter space. Approach. A computational model of epiretinal dual-electrode stimulation is developed to simulate the neural activity of a population of retinal ganglion cells (RGCs) under both synchronous and asynchronous stimulation conditions. The interaction between the electrode and RGCs under a range of stimulation parameters are simulated. Main results. Our simulation based on direct RGC activation suggests that VCs can be created using asynchronous stimulation. Two VC performance measures: 1) linearity in the change in centroid location of activated RGC populations, and 2) consistency in the size of activated RGC populations, have comparable performance under asynchronous and synchronous stimulation with appropriately selected stimulation parameters. Significance. Our findings support the possibility of creating VCs by directly activating RGCs under synchronous and asynchronous stimulation conditions. This study establishes the fundamental capability of VC creation based on temporal interactions within the RGC population alone and does not include the effects of potential indirect activation of any surviving inner retinal network neurons. Our results provide theoretical evidence for designing next-generation retinal prosthesis with higher spatial resolution.

An in-silico analysis of electrically evoked responses of midget and parasol retinal ganglion cells in different retinal regions

“…For multielectrode electrical stimulation, we distributed two electrodes of the same size along the y-axis for simultaneous stimulation. Two disk electrodes (platinum (Pt), conductivity: 8.9 × 10 6 S m −1 ) were embedded in the base (polyimide, conductivity: 1 × 10 −17 S m −1 ) with their lower surfaces attached to the upper surface of the VB [44]. We varied the electrode size (10 µm, 30 µm, 50 µm, 70 µm and 100 µm in diameter) and the minimum edge-to-edge distance (EED, from 10 to 180 µm in step of 5 µm) to predict the differential neural crosstalk (overlapping activated receptive field (RF) areas due to multiple electrode stimulation) induced by adjacent electrodes in CT and PT regions.…”

Challenges and Opportunities of Implantable Neural Interfaces: From Material, Electrochemical and Biological Perspectives

“…Notably, a single current source can be shared by multiple electrodes when applying asynchronous stimulation, which is more suitable for simplified stimulation devices and miniaturized high-density electrodes compared with synchronous stimulation. [84] Though using virtual electrodes may replace the complex electrode arrays, provide consistent long-term stimulation and improve the lifetime of implants, it will no longer work in case of physical electrode failure. [81] The stimulation mechanisms of vir-tual electrodes and the underlying neural activity response are still unclear entirely.…”

“…Notably, a single current source can be shared by multiple electrodes when applying asynchronous stimulation, which is more suitable for simplified stimulation devices and miniaturized high‐density electrodes compared with synchronous stimulation. [ 84 ]…”

Editorial: Advances in bioelectronics and stimulation strategies for next generation neuroprosthetics

“…Programming nerve stimulation setting is challenging and time consuming due to the huge number of possible stimulus parameter combinations (O'Doherty et al, 2011 ; Li et al, 2013 ; Yan et al, 2016 ; Jia et al, 2018 ; Guo et al, 2019 ; Muralidharan et al, 2020 ; Song et al, 2020 ; Zhang et al, 2020 ; Chang et al, 2022 ). In terms of FES, several “smart” strategies have been used to improve its effectiveness and acceptability.…”