Spatiotemporal properties of multipeaked electrically evoked potentials elicited by penetrative optic nerve stimulation in rabbits.

Purpose: To investigate the spatiotemporal properties of the cortical responses elicited by intraorbital optic nerve (ON) stimulation with penetrating electrodes as means of designing optimal stimulation strategies for an ON visual prosthesis.

Methods: The ON of rabbits was exposed by orbital surgery for electrical stimulation. Craniotomy was performed to expose the visual cortex contralateral to the operated eye. Electrically evoked potentials (EEPs) were recorded by an electrode array positioned on the visual cortex.

Results: There were primarily four components (N1, P1, P2, P3) in EEPs with implicit times of 8.0 ± 0.6, 11.3 ± 1.3, 20.5 ± 1.4, and 26.9 ± 1.5 ms, respectively, when the ON was stimulated by penetrating electrodes. The thresholds to elicit these components were different, and the higher thresholds were seen with slower cortical components. The corresponding thresholds were 13.8 ± 3.1 μA for N1, 21.8 ± 4.7 μA for P1, 36.4 ± 11.4 μA for P2, and 68.4 ± 17.2 μA for P3. The time courses of the EEP components were also distinct. The locations of EEPs with the maximum P1 amplitude showed a spatial correspondence to the ON stimulation sites. Different profiles of cortical responses could be discriminated when the ON stimulation sites were separated by 150 μm.

Conclusions: Multiple components with different properties were elicited in EEPs when the ON was stimulated by penetrating electrodes. Retinotopic and localized stimulation could be achieved with this stimulating approach.