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Q. Ren, J. Sun, L. Li, Y. Lu, P. Cao, Y. Yan, X. Chai; Spatiotemporal Properties of Multi-Peaked Electrically Evoked Potentials Elicited by Penetrative Optic Nerve Stimulation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3031. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study is to investigate the spatiotemporal properties of the multi-peaked responses of visual cortex elicited by intraorbital optic nerve (ON) stimulation with penetrating electrodes to evaluate the feasibility of an ON visual prosthesis based on penetrative stimulation. Stimulating strategies for selective stimulation of different fibers were investigated as well.
Chinese albino rabbits, weighting ~ 2.0-2.5 kg, were used in the experiments. After animal anesthesia, craniotomy was performed to expose the contra-lateral visual cortex to the operated eye. Orbital surgery was then performed to expose the ON. Teflon-insulated platinum-iridium wire electrodes were inserted into the ON for electrical stimulation. Multi-channel electrically evoked cortical potentials (EEP) were recorded simultaneously with a 4×4 silver-ball electrode array on the visual cortex.
There are mainly four components (N1, P1, P2, and P3) in EEP when the ON was stimulated by penetrating electrodes. The component with slower implicit time showed a higher threshold. The different components also showed a distinct time course. The amplitudes of N1, P1 and P2 increased nearly linearly with increment in current strength from 25 µA to 100 µA, and the dynamic ranges of these components were at least 0.6 log units (12.5 to 50 nC). The faster component (P1) may reflect the synaptic inputs generated via the faster conducting axons, and the slower ones (P2, P3) may be related to a combination of potentials generated via slower conducting axons, intracortical signaling as well as collicular inputs via the thalamus. The location of the EEPs with the maximum P1 amplitude showed a spatial correspondence to the ON stimulation sites. ON stimulation by penetrating electrodes could perform relatively localized stimulation and different cortical response profiles could be discriminated when the ON stimulation sites were separated by 150µm. A stimulus pulse with hyperpolarizing or depolarizing pre-pulse could facilitate or restrain the P1 response without affecting other components obviously, which indicates that an optimal stimulating strategy may be established to selectively activate different fibers to restore distinct visual information by an ON visual prosthesis with penetrative stimulation.
ON stimulation can elicit phosphenes over a larger visual field, and one electrode pair may induce different phosphene patterns rather than a single point with different stimulating parameters.
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