ABNORMAL IPSILATERAL VISUAL-FIELD REPRESENTATION IN AREA-17 AND AREA-18 OF HYPOPIGMENTED CATS

We compared the central projections of retinal ganglion cells in tempo ral retina and the cortical representation of visual fields in areas 1 7 and 18 in cats with various hypopigmentation phenotypes (albino, het erozygous albino, Siamese, and heterozygous Siamese). In all cats stud ied, we found that the extent of abnormal ipsilateral visual field rep resentation varied widely, and more of the ipsilateral visual field wa s represented in area 18 than in area 17. The greatest degree of ipsil ateral visual field representation was found in albino cats, followed by Siamese, heterozygous albino and heterozygote Siamese cats, respect ively. Additionally, in the different groups there was wide variation in the numbers of contralaterally projecting alpha and beta ganglion c ells in temporal retina. In all cases, however, contralaterally projec ting alpha cells were found to extend further into temporal retina tha n beta cells. We found that in each cat studied, the maximum extent of the abnormal ipsilateral visual field representation in areas 18 and 17 corresponded to the location of the 50% decussation line (i.e., the point where 50% of the ganglion cells in temporal retina project to t he contralateral hemisphere) for alpha and beta cells, respectively, f or that cat. Our results suggest that the extent of the abnormal visua l field representations in visual cortex of hypopigmented cats reflect s the extent of contralaterally projecting retinal ganglion cells in t emporal retina. (C) 1995 Wiley-Liss, Inc.