Time-dependent decrease in the extent of visual deafferentation in the lateral geniculate nucleus of adult cats with small retinal lesions.

Small, round photocoagulator lesions of 3-6 degrees (0.6-1.2 mm) diameter were placed nasally on the retina of adult cats. Histological controls proved the complete destruction of all retinal layers within the lesions. Changes in lesion size by shrinkage of the retinal scar did not exceed 0.1 mm or 0.5 degrees. At different times after photocoagulation, single cells were recorded in layers A and A1 of the contralateral lateral geniculate nucleus (LGN) with tungsten microelectrodes. Acute lesions of this size completely deafferented single LGN cells in layer A whose receptive field (RF) area was within the lesion. Thirty days and more after coagulation, light-excitable cells were detected in the originally deafferented LGN region, with RFs in the immediate surround of the retinal lesion. The spontaneous activity and light excitability of these neurons were altered. The representation of 3-4 degrees retinal lesions at 20 degrees horizontal eccentricity was found to be completely filled in by excitation in the LGN. Excitation had spread from the unsevered parts of the retina into the region of deafferentation. Single cells with signs of multiple activation from more than one border region of the retinal lesion were occasionally detected.