Retinotopic organization of areas 18 and 19 in the cat.

The location and retinotopic organization of areas 18 and 19 in cat cortex were determined using electrophysiological mapping techniques. These two areas each contain a single representation of the visual hemifield and each has a distinctive cytoarchitecture. The visual hemifield representations in these two areas are nearly mirror images of each other. Compared to area 17, areas 18 and 19 have less cortical surface area, have a lower cortical magnification factor, contain less of the visual field and contain second order instead of first order transformations of the visual hemifield. An unusual asymmetry was found between the representations of the upper and lower visual quadrants not seen before in maps of other areas of cat or other species. A considerable amount of variability in the retinotopic organization of these two areas was found among cats.