Response properties of electrically evoked potential elicited by multi-channel penetrative optic nerve stimulation in rabbits

Visual prosthesis is a potential way to restore partial vision for the patients with degenerative retinal diseases such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Optic nerve stimulation with penetrating microelectrode array has been suggested as a possible method for visual prosthesis. The purpose of this study was to investigate the feasibility and basic response properties of cortical responses elicited by optic nerve stimulation with penetrating electrodes in rabbits. In this study, three triangularly or linearly configured platinum-iridium wire electrodes were inserted into the optic nerves of rabbits for electrical stimulation. The charge-balanced current pulses with amplitudes ranging from 10 to 100 mu A at 0.5 ms pulse duration were used as the electrical stimuli. The electrically evoked potentials (EEPs) were recorded with a 16-channel silver-ball electrode array in the rabbit visual cortex. Our experimental results showed that the activities of visual cortex could be effectively evoked by the optic nerve stimulation with penetrating electrodes. The threshold of current and charge density to elicit EEPs under optic nerve stimulation at 0.5 ms pulse duration was 20.3 +/- A 7.5 mu A and 37.8 +/- A 13.9 mu C/cm(2), respectively. Current stimuli with cathode-first pulses elicited larger cortical responses than that with anode-first pulses. The amplitude of P1 and extent of EEPs increased as the stimulating current amplitude increased, while the latency of P1 decreased. The spatial distributions of multi-channel EEPs in visual cortex demonstrated distinctively different properties under stimulation with different orientations of the stimulating electrodes.