Item

Abstract

Visual receptive fields have dynamic properties that may change with the conditions of visual stimulation or with the state of chronic visual deprivation. We used 4.7 Tesla functional magnetic resonance imaging (fMRI) to study the visual cortex of two adult normal macaque monkeys and one with binocular central retinal lesions due to a formof juvenile macular degeneration (MD). FMRI experiments were performed under light remifentanyl induced anesthesia
(Logothetis, et al., Nature Neuroscience, 1999). Standard moving horizontal/vertical bar stimuli were presented to the subjects and the population receptive field (pRF) method (Dumoulin and Wandell, Neuroimage 2008) was used to measure retinotopic maps and pRF sizes in early visual areas. In addition we used a new spatiotemporal dynamic modulation method to measure pRF sizes as comparison. In general fMRI measurements from the normal monkeys agree
with electrophysiological results in the literature, with fMRI pRF sizes and electrophysiology measurements showing similar trends. For the MD monkey, the size and location of the fMRI defined lesion projection zone (LPZ) in early visual areas is consistent with the retinotopic projection
of the retinal lesion. No significant activity is found within V1 LPZ of the MD monkey, and the retinotopic organization of the non-deafferented V1 periphery is regular without distortion.
Higher level visual areas (V5/MT) of the MD monkey show more extensive activation than areas of control monkeys with an artificial scotoma (to obscure part of the stimuli from the visual field as a simulation of the real scotoma) of comparable size. PRF sizes in the nondeafferented
V5/MT of the MD monkey are on average slightly smaller than controls. Further investigation using fMRI and standard electrophysiology methods is in progress.