SURFACE-VIEW CONNECTIVITY PATTERNS OF AREA-18 IN CATS

To determine surface-view connectivity patterns of area 18, separate i njections of up to six anatomical tracers were delivered to various ro strocaudal locations of area 18 in six normal cats. Subsequently, cort ex was separated from subcortical structures, manually flattened, and cut parallel to the surface. Results reveal that ipsilateral cortical connections of area 18 with three regions of cortex are topological. I n areas 17 and 19, separate patches of cells labeled with different tr acers progressed in a rostrocaudal sequence corresponding to the order of the injections. A similar but less precise pattern of rostrocaudal labeling occurred in more lateral visual cortex, even though several presumptive visual areas were involved. Thus, anteromedial suprasylvia n cortex projected to anterior area 18 while more posterolateral supra sylvian cortex projected to posterior area 18. There was no evidence o f double-labeled cells projecting to separate regions in area 18. Thes e results are more consistent with the concept of a single suprasylvia n area projecting to area 18 cortex than several.