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Q. Ren, C. Cai, L. Li, X. Li, X. Chai; Spatiotemporal Properties of Multi-Channel Cortical Responses Elicited by Optic Nerve Stimulation in Rabbits. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3033.
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To investigate the basic spatiotemporal properties of cortical responses elicited by optic nerve stimulation with penetrating electrodes using multi-channel recording electrode array implanted into the visual cortex area in rabbits.
Thirteen healthy adult Chinese albino rabbits, weighting about 2.0~2.5 kg, were used in the experiments. Craniotomy was performed on the rabbit occipital to expose the contra-lateral visual cortex to the operated eye. Then orbital surgery was performed to expose the optic nerve. For electrical stimulation, triangularly or linearly configured three platinum-iridium wire electrodes insulated by Teflon were inserted into the optic nerves of rabbits. The charge-balanced current pulses with amplitudes ranging from 10 to 100 µA at 0.5 ms pulse duration were used as the stimuli. The electrically evoked potentials (EEP) were recorded with a 16-channel silver-ball electrode array at the visual cortex. Electroretinograms (ERG) and visual evoked potentials (VEP) were monitored as a control at the different stages of the experiment.
The experimental results showed that ERG didn’t vary significantly, but the P1 amplitude of VEP declined after the orbital surgery to expose optic nerve. EEP could be elicited by bipolar current stimulation using different pairs of the three electrodes. The threshold of current and charge density for optic nerve stimulation at 0.5ms pulse duration was 20.3 ± 7.5 µA and 37.8 ± 13.9 µC/cm2, respectively. The intensity (P1 amplitude) and extend of EEP increased as the stimulating current amplitude increased, while the latency of P1 decreased. Current stimuli with cathode-first pulses elicited larger cortical responses than that with anode-first pulses. The spatial distributions of multi-channel EEP demonstrated distinctively different properties under stimulation with different orientations of the stimulating electrodes.
The visual cortex could be effectively evoked by the optic nerve stimulation with penetrating electrodes, and different spatiotemporal responses could be elicited by changing the stimulating pulse parameters as well as the spatial orientation of the stimulating electrodes.
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