Comparison of Activated Cortical Area Between Light and Electrical Stimulation in Rabbit Retina by Positron Emission Tomography

Abstract

Purpose: : Electrical stimulation of the retina can elicit cortical potentials in animals and phosphenes in humans. (Dowling 2005, Weiland 2005) By using positron emission tomography (PET), the cortical areas of a rabbit activated by light and electrical stimuli were evaluated and the nature of the electrically evoked visual perception was analyzed by comparing the two activated cortical images.

Methods: : New Zealand white rabbit weighing 3.0kg was used in the study. Static PET data with 10 min duration was acquired 30 min after injection of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG, 37 MBq) through the catheter placed in the ear vein. The resting PET study was done without stimuli. For the light stimulation PET studies, repetitive flash light stimulation of whole visual field (0.3 Hz, 6 min total) was applied on one eye 1 min prior to FDG injection. For the electrical stimulation PET studies, repetitive electrical retinal stimulation (500µA, 1 Hz, 6 min total) was applied on the same eye with light stimulation using a suprachoroidal polyimide electrode array placed under the visual streak. Each study was performed on different day. All images were realigned to the resting state image. The quantitative change of cerebral glucose metabolism was determined from the difference between the resting and stimulation state. To remove the effects of global differences, each voxel value of the images was normalized by the mean value of the whole brain.

Results: : After visual and electrical stimulation of the rabbit retina, the cerebral areas of increased metabolism could be localized on PET study. The activated cortical area after electrical retinal stimulation overlapped and confined within the visually activated cortical area.

Conclusions: : The PET study showed increased metabolism of the same cortical area on light and electrical stimulation of the rabbit retina, which indicated electrical retinal stimulation could induce visual perception similar to the light stimulation in the rabbit.

Keywords: retina • visual cortex