Three-dimensional multilayer concentric bipolar electrodes restrict spatial activation in optic nerve stimulation.

Objective.Intraneural nerve interfaces often operate in a monopolar configuration with a common and distant ground electrode. This configuration leads to a wide spreading of the electric field. Therefore, this approach is suboptimal for intraneural nerve interfaces when selective stimulation is required.Approach.We designed a multilayer electrode array embedding three-dimensional concentric bipolar (CB) electrodes. First, we validated the higher stimulation selectivity of this new electrode array compared to classical monopolar stimulation using simulations. Next, we compared themin-vivoby intraneural stimulation of the rabbit optic nerve and recording evoked potentials in the primary visual cortex.Main results.Simulations showed that three-dimensional CB electrodes provide a high localisation of the electric field in the tissue so that electrodes are electrically independent even for high electrode density. Experimentsin-vivohighlighted that this configuration restricts spatial activation in the visual cortex due to the fewer fibres activated by the electric stimulus in the nerve.Significance.Highly focused electric stimulation is crucial to achieving high selectivity in fibre activation. The multilayer array embedding three-dimensional CB electrodes improves selectivity in optic nerve stimulation. This approach is suitable for other neural applications, including bioelectronic medicine.

A machine-learning algorithm correctly classifies cortical evoked potentials from both visual stimulation and electrical stimulation of the optic nerve.

Objective. Optic nerve's intraneural stimulation is an emerging neuroprosthetic approach to provide artificial vision to totally blind patients. An open question is the possibility to evoke individual non-overlapping phosphenes via selective intraneural optic nerve stimulation. To begin answering this question, first, we aim at showing in preclinical experiments with animals that each intraneural electrode could evoke a distinguishable activity pattern in the primary visual cortex.Approach. We performed both patterned visual stimulation and patterned electrical stimulation in healthy rabbits while recording evoked cortical activity with an electrocorticogram array in the primary visual cortex. Electrical stimulation was delivered to the optic nerve with the intraneural array OpticSELINE. We used a support vector machine algorithm paired to a linear regression model to classify cortical responses originating from visual stimuli located in different portions of the visual field and electrical stimuli from the different electrodes of the OpticSELINE.Main results. Cortical activity induced by visual and electrical stimulation could be classified with nearly 100% accuracy relative to the specific location in the visual field or electrode in the array from which it originated. For visual stimulation, the accuracy increased with the separation of the stimuli and reached 100% for separation higher than 7°. For electrical stimulation, at low current amplitudes, the accuracy increased with the distance between electrodes, while at higher current amplitudes, the accuracy was nearly 100% already for the shortest separation.Significance. Optic nerve's intraneural stimulation with the OpticSELINE induced discernible cortical activity patterns. These results represent a necessary condition for an optic nerve prosthesis to deliver vision with non-overlapping phosphene. However, clinical investigations will be required to assess the translation of these results into perceptual phenomena.

Spatially selective activation of the visual cortex via intraneural stimulation of the optic nerve.

Retinal prostheses can restore a functional form of vision in patients affected by dystrophies of the outer retinal layer. Beyond clinical utility, prostheses for the stimulation of the optic nerve, the visual thalamus or the visual cortex could also serve as tools for studying the visual system. Optic-nerve stimulation is particularly promising because it directly activates nerve fibres, takes advantage of the high-level information processing occurring downstream in the visual pathway, does not require optical transparency and could be effective in cases of eye trauma. Here we show, in anaesthetized rabbits and with support from numerical modelling, that an intraneural electrode array with high mechanical stability placed in the intracranial segment of the optic nerve induces, on electrical stimulation, selective activation patterns in the visual cortex. These patterns are measured as electrically evoked cortical potentials via an ECoG array placed in the contralateral cortex. The intraneural electrode array should enable further investigations of the effects of electrical stimulation in the visual system and could be further developed as a visual prosthesis for blind patients.