Functional organization of columns in damaged visual cortex of adult cats

Objective: The objective of the present study was to reveal the amount of preservation of the most prominent features of the visual cortex: orientation and ocular dominance columns. It has been assumed that because of its inherent organization, the fragment of cells that would survive following lesioning would preserve the orientation and ocular dominance properties, despite the distortion of the connectivity pattern. Experimental: The experiments were carried out on 13 anesthetized and paralyzed adult cats from which 1186 single cells were recorded. The animals were divided into the following three experimental (operated) groups to observe the time lapse of changes after operation: Acute (immediately); Short Chronic (2 to 3 months), and Long Chronic (5 to 7 months). The operations were performed using microsurgical, stereotaxic, electrophysiological, and histological techniques. The disconnection was produced by making a surgical incision into the visual cortex perpendicular to the cortical columns as accurately as possible. The single-unit activity of cells was recorded in the areas proximal and distal to the lesion. Results: In all groups, the visual responsiveness of the cells was significantly reduced and the percentage of binocular cells was significantly lower in all recording sites. The distribution of the cells according to their ocular dominance was similar to that in the normal control group. Surprisingly, most of the cells, that remained visually active, were found selective to orientation in all experimental groups as well as in the normal control group. Conclusion: Even though no improvement in function occurred because mature cells were involved, the inherent structure of the disrupted cortical columns in the visual cortex was preserved. Therefore, the disruption of cortical connections does not lead to remarkable distortion of the inherent connectivity pattern on the whole in visually active cortical fragments.