gms | German Medical Science

Objective: This study investigates low-frequency sinusoidal electrical stimulation as a method for improving focal activation of retinal ganglion cells (RGCs) while minimizing unintended axonal stimulation, with the goal of enhancing precision in retinal prosthetic systems.

Materials and Methods: RGC responses to epiretinal sinusoidal stimulation at frequencies between 40 and 100 Hz were studied in ex vivo degenerated (rd10) mouse retinas using a high-density CMOS-based Micro-Electrode Array. Additionally, spatial discrimination based on RGC output upon simple object sinusoidal stimulation was tested using a logistic regression classifier.

Results: Sinusoidal stimulation at 40 Hz and 60 Hz avoided distal axonal activation at stimulation amplitudes of 0.23 µA (17.3 µC cm⁻²) and 0.28 µA (14.8 µC cm⁻²), respectively, while maintaining focal activation of RGCs. Distinct spiking activity of selected RGCs enabled the classification of overlapping, spatially displaced objects (separated by 1°). Using a regularized logistic regression classifier, spatially displaced objects with sizes of 5.5° and 3.5° were discriminated with accuracies of 90% and 62%, respectively. Furthermore, low artificial contrast (10%) allowed for 80% classification accuracy for larger objects (5.5°).

Discussion: Sinusoidal stimulation demonstrated potential for achieving localized neuronal activation and selective RGC stimulation, avoiding unwanted axonal activation. This method offers a promising improvement in spatial and contrast resolution for retinal neuroprosthetics, addressing critical limitations in current systems.

Acknowledgment: This work was supported by the German Research Foundation (DFG, SFB 1233 'Robust Vision', Project Number 2766935) and by the Hochschuljubiläumsfonds der Stadt Wien (H-864102/2022)