Korean J Ophthalmol.  2014 Aug;28(4):337-342.

Lateral Geniculate Body Evoked Potentials Elicited by Visual and Electrical Stimulation

• Choi CW
• Kim PS
• Shin SA
• Yang JY
• Yang YS

Abstract

PURPOSE
Blind individuals who have photoreceptor loss are known to perceive phosphenes with electrical stimulation of their remaining retinal ganglion cells. We proposed that implantable lateral geniculate body (LGB) stimulus electrode arrays could be used to generate phosphene vision. We attempted to refine the basic reference of the electrical evoked potentials (EEPs) elicited by microelectrical stimulations of the optic nerve, optic tract and LGB of a domestic pig, and then compared it to visual evoked potentials (VEPs) elicited by short-flash stimuli.
METHODS
For visual function measurement, VEPs in response to short-flash stimuli on the left eye of the domestic pig were assessed over the visual cortex at position Oz with the reference electrode at Fz. After anesthesia, linearly configured platinum wire electrodes were inserted into the optic nerve, optic track and LGB. To determine the optimal stimulus current, EEPs were recorded repeatedly with controlling the pulse and power. The threshold of current and charge density to elicit EEPs at 0.3 ms pulse duration was about ±10 microA.
RESULTS
Our experimental results showed that visual cortex activity can be effectively evoked by stimulation of the optic nerve, optic tract and LGB using penetrating electrodes. The latency of P1 was more shortened as the electrical stimulation was closer to LGB. The EEPs of two-channel in the visual cortex demonstrated a similar pattern with stimulation of different spots of the stimulating electrodes. We found that the LGB-stimulated EEP pattern was very similar to the simultaneously generated VEP on the control side, although implicit time deferred.
CONCLUSIONS
EEPs and VEPs derived from visual-system stimulation were compared. The LGB-stimulated EEP wave demonstrated a similar pattern to the VEP waveform except implicit time, indicating prosthetic-based electrical stimulation of the LGB could be utilized for the blind to perceive vision of phosphenes.

Keyword

Electrical evoked potentials; Geniculate bodies; Visual evoked potentials

MeSH Terms

Animals
Electric Stimulation
Electrodes, Implanted
Evoked Potentials, Visual/*physiology
Geniculate Bodies/*physiology
Male
Optic Nerve/physiology
Optic Tract/physiology
Photic Stimulation
Sus scrofa
Visual Cortex/*physiology

Figure

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  Fig. 1 Diagram of the procedure and taking the visual evoked potential (VEP) and electrical evoked potential (EEP) in this study. LGB = lateral geniculate body.

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  Fig. 2 The surgical approach to the retrobulbar optic nerve. Implantation of platinum wire electrode into the optic nerve.

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  Fig. 3 Visual evoked potentials (VEPs) to the flash stimuli for the controlled object. (A) VEPs to the flash stimuli on a left eye. (B) VEPs to the flash stimuli on a right eye (before optic nerve was severed).

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  Fig. 4 Electrically-evoked potential (EEP) of optic nerve, optic track and lateral geniculate body (LGB). (A) Visual evoked potentials (VEPs) in response to short flash stimuli on a right eye of the pig after optic nerve was severed (control). (B) EEPs to electrical stimulations on optic nerve (right eye side). (C) EEPs to electrical stimulations on optic track before optic chiasm (right eye side). (D) EEPs to electrical stimulations on optic track after optic chiasm (right eye side). (E) EEPs to electrical stimulations on LGB (right eye side).

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  Fig. 5 Visual evoked potentials to flash stimuli on a left eye after the skull of the animal were opened (direct over the visual cortex at Oz referenced with Fz).

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