New publication on the avoidance of axonal activation in epiretinal stimulation experiments

A new paper by A. Corna (first author) and members of our institute has been published recently in the 'Journal of Neural Engineering'. The authors demonstrate the avoidance of axonal activation in epiretinal stimulation experiments. Congratulations!

The images show a retina sample placed on a CMOS-based HD MEA and the current generated by the capacitive stimulation electrode.

© Andrea Corna et al 2024 J. Neural Eng. 21 026036

Bidirectional High-Resolution retina interface. (A) A retina sample on the CMOS-based HD MEA. (B) The stimulation currents.

Abstract:

Objective: Neuromodulation, particularly electrical stimulation, necessitates high spatial resolution to achieve artificial vision with high acuity. In epiretinal implants, this is hindered by the undesired activation of distal axons. Here, we investigate focal and axonal activation of retinal ganglion cells (RGCs) in epiretinal configuration for different sinusoidal stimulation frequencies.

Approach: RGC responses to epiretinal sinusoidal stimulation at frequencies between 40 and 100 Hz were tested in ex-vivo photoreceptor degenerated (rd10) isolated retinae. Experiments were conducted using a high-density CMOS-based microelectrode array, which allows to localize RGC cell bodies and axons at high spatial resolution.

Main results: We report current and charge density thresholds for focal and distal axon activation at stimulation frequencies of 40, 60, 80, and 100 Hz for an electrode size with an effective area of 0.01 mm2. Activation of distal axons is avoided up to a stimulation amplitude of 0.23 µA (corresponding to 17.3 µC cm−2) at 40 Hz and up to a stimulation amplitude of 0.28 µA (14.8 µC cm−2) at 60 Hz. The threshold ratio between focal and axonal activation increases from 1.1 for 100 Hz up to 1.6 for 60 Hz, while at 40 Hz stimulation frequency, almost no axonal responses were detected in the tested intensity range. With the use of synaptic blockers, we demonstrate the underlying direct activation mechanism of the ganglion cells. Finally, using high-resolution electrical imaging and label-free electrophysiological axon tracking, we demonstrate the extent of activation in axon bundles.

Significance: Our results can be exploited to define a spatially selective stimulation strategy avoiding axonal activation in future retinal implants, thereby solving one of the major limitations of artificial vision. The results may be extended to other fields of neuroprosthetics to achieve selective focal electrical stimulation.

 

Paper: Avoidance of axonal stimulation with sinusoidal epiretinal stimulation, opens an external URL in a new window