Avoidance of axonal stimulation with sinusoidal epiretinal stimulation.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Ophthalmology

Background:

• High spatial resolution in neuromodulation, especially electrical stimulation, is crucial for achieving high-acuity artificial vision.
• Epiretinal implants face challenges with undesired distal axon activation, limiting the effectiveness of visual prostheses.
• Understanding the precise activation patterns of retinal ganglion cells (RGCs) is key to overcoming these limitations.

Purpose of the Study:

• To investigate the focal and axonal activation of RGCs using epiretinal sinusoidal stimulation at various frequencies.
• To determine stimulation parameters that allow for selective RGC activation while avoiding distal axon stimulation.
• To inform the development of improved strategies for artificial vision.

Main Methods:

• Experiments were conducted on ex-vivo retinae from photoreceptor degenerated (rd10) mice.
• A high-density CMOS-based microelectrode array was used for high-resolution localization of RGCs and their axons.
• Sinusoidal stimulation frequencies ranged from 40 to 100 Hz, with analysis of current and charge density thresholds.

Main Results:

• Current and charge density thresholds for focal and distal axon activation were determined for frequencies of 40, 60, 80, and 100 Hz.
• Distal axon activation was successfully avoided up to specific stimulation amplitudes at 40 Hz (0.23 µA) and 60 Hz (0.28 µA).
• The ratio of focal to axonal activation thresholds increased with decreasing frequency, with minimal axonal response at 40 Hz.

Conclusions:

• Results provide a basis for defining spatially selective stimulation strategies to avoid axonal activation in retinal implants.
• This research addresses a significant limitation in current artificial vision technology.
• The findings have potential applications in other neuroprosthetic fields requiring focal electrical stimulation.