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 41/2, m onths prior to electrophysiological recording. This produced lesion pr ojection zones (LPZs) in V1, 1.6-9.5 mm wide, that were deprived of th eir normal input from one eye, but that received a normal input from t he other eye, Nevertheless, at the majority of recording sites within these zones neuronal responses were elicited by stimulation of the les ioned eye, with receptive fields being displaced onto regions of retin a surrounding the lesion, while receptive fields determined through st imulation of the normal eye followed the normal visuotopic organizatio n of V1. However, neuronal responses to stimulation of the lesioned ey e within the LPZs were characterized by rapid habituation and unusuall y low firing rates in comparison with responses to stimulation of the normal eye, Stimulation of the normal eye temporarily masked the respo nsiveness 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 tes t eye were found up to 3.6 mm from the perimeter of the LPZs, and ther efore the shifts in the visuotopic map caused by retinal lesions canno t 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 la yers, and lowest in the supragranular layers, By combining a restricte d lesion of one eye with laser photocoagulation of the optic disc of t he other eye, the effects of deactivation of the normal eye on the les ion-induced visuotopic reorganization were also investigated. Neither chronic nor acute deactivation produced any discernible further change s in visuotopy or in the characteristics of neuronal responses to stim ulation of the eye with the discrete lesions. Our findings show that t he representations of the two eyes in adult visual cortex are capable of independent reorganization, These findings parallel those of work i n auditory cortex, suggesting that topographic reorganization in prima ry sensory areas of adult cortex may be governed by similar mechanisms .