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Abstract #9148 Published in IGR 5-2
The representation of retinal blood vessels in primate striate cortex
Adams DL; Horton JCJournal of Neuroscience 2003; 23: 5984-5997
The blood vessels that nourish the inner retina cast shadows on photoreceptors, creating 'angioscotomas' in the visual field. The authors have found the representations of angioscotomas in striate cortex of the squirrel monkey. These were detected in nine of 12 normal adult animals by staining flatmounts for cytochrome oxidase activity after enucleation of one eye. They appeared as thin profiles in layer 4C radiating from the blind spot representation. Angioscotomas can be regarded as a local form of amblyopia. After birth, when light strikes the retina, photoreceptors beneath blood vessels are denied normal visual stimulation. This deprivation induces remodeling of geniculocortical afferents in a distribution that corresponds to the retinal vascular tree. Angioscotoma representations were most obvious in monkeys with fine ocular dominance columns and were invisible in monkeys with large, well segregated columns. In monkeys without columns, their width corresponded faithfully to the inducing retinal shadow, making it possible to calculate the minimum shadow required to produce a cortical representation. The 'amblyogenic threshold' was calculated as the fraction of the pupil area eclipsed to trigger remodeling of geniculocortical afferents. It was found to be constant over retinal eccentricity, vessel size, and shadow size. Ambliogenic shadows only three to four cones wide were sufficient to generate a cortical representation, testifying to the remarkable precision of the cortical map. The representations of retinal blood vessels separated by only 0.65 degrees were resolvable in the cortex, yielding an upper limit on cortical resolution of 340 μm in layer 4C.
Dr. D.L. Adams, Beckman Vision Center, University of California, San Francisco, San Francisco, CA 94143-0730, USA. dadams@itsa.ucsf.edu
Classification:
5 Experimental glaucoma; animal models
