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Q. Ren, J. Sun, L. Li, Y. Lu, C. Cai, X. Li, P. Cao, Y. Chai, X. Sui; Multi-Peak Responses of Visual Cortex Elicited by Intraorbital Optic Nerve Electrical Stimulation in Rabbits. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4588.
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The purpose of this study is to investigate the spatiotemporal properties of the multi-peak responses of visual cortex elicited by intraorbital optic nerve stimulation with penetrating electrodes.
Healthy adult Chinese albino rabbits with weight about 2.0~2.5 kg were used in the experiments. After animal anesthesia, scalp along mid-vertical meridian was incised and removed. 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, Teflon-insulated platinum-iridium wire electrodes with different configuration were inserted into the optic nerves of rabbits. Charge-balanced biphasic current pulses with varied parameters were applied to the different pairs of the stimulating electrodes. Multi-channel electrically evoked cortical potentials (EEPs) were recorded simultaneously with a 4×4 silver-ball electrode array at the visual cortex.
Multi-peak EEPs were often recorded at the visual cortex as the optic nerve was stimulated by penetrating electrodes. By gradually changing the stimulating current amplitude from 5 to 100µA, a negative wave (N1) with short latency was first recorded and several positive waves (P1, P2, P3) with longer latencies turned up gradually with the increment of the current strength. N1, P1, P2, and P3 wave showed latencies at 8.04+0.63, 11.33+1.29, 20.52 +1.40, and 26.86+1.47ms, respectively, and the corresponding thresholds were 13.75+3.06, 21.79+4.72, 36.43+11.44, and 68.40+17.23µA, respectively. Furthermore, the fast positive wave P1 is narrower than others and tends to locate at temporal lateral cortex while slow positive waves at the middle cortex.
Different waves in EEPs might be produced by activation of different groups of optic nerve fibers which have different conducting velocities and represent distinct information of the visual inputs. The different thresholds for different fiber groups suggest that an optimal stimulating strategy may be established to selectively activate the different optic nerve fibers to restore distinct visual information by an optic nerve visual prosthesis.
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