An in-vivo paradigm for the evaluation of stimulating electrodes for use with a visual prosthesis.
BACKGROUND
Electrical stimulation of the visual cortex with surface electrodes is able to elicit basic visual perceptions in blind patients. The development of a visual prosthesis for the blind will require an in-vivo model for the optimization of cortical neurostimulation with multielectrode arrays.


METHODS
In anaesthetized cats a bilateral craniotomy was performed and the dura was removed to expose the cerebral cortex. A prototype stimulating electrode array was placed on a gyrus in one hemisphere, and the transcallosal evoked response (TER) to cortical stimulation by this electrode array was recorded at a homologous region in the contralateral hemisphere.


RESULTS
The stimulating electrode array elicited TER of short latency (6.9 ms) in the contralateral hemisphere. Bipolar stimulation of adjacent electrodes on the array evoked similar TER regardless of the polarity of stimulation. Electrodes spread apart on the array caused higher amplitude TER than electrodes placed close together. Multielectrode stimulation evoked lower amplitude TER than bipolar stimulation.


CONCLUSIONS
This transcallosal model of cortical neurostimulation is a useful method to evaluate electrode arrays and stimulation techniques in the development of a visual prosthesis.
Chowdhury
Vivek
V
Department of Ophthalmology, Prince of Wales Clinical School, University of New South Wales, Sydney, New South Wales, Australia. vivekc@bigpond.com
Morley
John W
JW
Coroneo
Minas T
MT
D000818:Animals; D002415:Cats; D004558:Electric Stimulation / Q000379:methods*; D004567:Electrodes, Implanted; D010719:Phosphenes; D014793:Visual Cortex / Q000502:physiology*