Visuotopic reorganization in the primary visual cortex of adult cats following monocular and binocular retinal lesions
The effect of discrete monocular retinal lesions on the representation of the visual field in the primary visual area (V1) was investigated in adult cats. Lesions were created using argon lasers, 8 d to 4 1/2, months prior to electrophysiological recording. This produced lesion projection zones (LPZs) in V1, 1.6-9.5 mm wide, that were deprived of their normal input from one eye, but that received a normal input from the other eye, Nevertheless, at the majority of recording sites within these zones neuronal responses were elicited by stimulation of the lesioned eye, with receptive fields being displaced onto regions of retina surrounding the lesion, while receptive fields determined through stimulation of the normal eye followed the normal visuotopic organization of V1. However, neuronal responses to stimulation of the lesioned eye within the LPZs were characterized by rapid habituation and unusually low firing rates in comparison with responses to stimulation of the normal eye, Stimulation of the normal eye temporarily masked the responsiveness of neurons within the LPZ to stimulation of the lesioned eye, The proportion of neurons responsive to stimulation of the lesioned eye was higher just inside the borders of the LPZs than at the centers of these zones. However, neurons responsive to stimulation of the test eye were found up to 3.6 mm from the perimeter of the LPZs, and therefore the shifts in the visuotopic map caused by retinal lesions cannot he explained solely on the basis of the normal scatter of receptive fields and point-image size in V1. The proportion of cells responsive to stimulation of the lesioned eye was highest in the infragranular layers, and lowest in the supragranular layers, By combining a restricted lesion of one eye with laser photocoagulation of the optic disc of the other eye, the effects of deactivation of the normal eye on the lesion-induced visuotopic reorganization were also investigated. Neither chronic nor acute deactivation produced any discernible further changes in visuotopy or in the characteristics of neuronal responses to stimulation of the eye with the discrete lesions. Our findings show that the representations of the two eyes in adult visual cortex are capable of independent reorganization, These findings parallel those of work in auditory cortex, suggesting that topographic reorganization in primary sensory areas of adult cortex may be governed by similar mechanisms.