The location and retinotopic organization of visual areas in the cat cortex were determined by systematically mapping visual cortex in over 100 cats. The positions of the receptive fields of single neurons or small clusters of neurons were related to the locations of the corresponding recording sites in the cortex to determine the representations of the visual field in these cortical areas. In this report, the first of a series, we describe the organization of area 17. A single representation of the cat's entire visual field corresponds closely to the cytoarchitectonically defined area 17. This area has the largest cortical surface area (380 mm2) and the highest cortical magnification factor (3.6 mm2/degree2 at area centralis) of all the cortical areas we have studied. There was perfect agreement between the borders of area 17 determined electrophysiologically and cytoarchitecturally. This area contains a first order transformation of the visual hemifield in which every adjacent point in the visual field is represented as an adjacent point in the cortex. Some variability exists among cats in the extent and retinotopic representation of the visual field in area 17.

This is the second in a series of papers in which we describe our continuing efforts to define functional units of visual cortex based upon electro-physiological mapping of single and multiple unit activity in both awake and the nitrous oxide anesthetized cats. In the first paper (Tusa, Palmer and Rosenquist, '78), the extent and retinotopic organization of area 17 were described. In this paper, we describe the somewhat more complex organization of the visual cortex lying on the banks of the middle and posterior suprasylvian sulci. This region of cortex consists of six retinotopically organized units. These areas are arranged as three roughly mirror symmetrical pairs separated in each case by the fundus of the middle or posterior suprasylvian sulci. Some thalamo-cortical autoradiographic material is presented which supports this parcellation of the cortex.

No abstract

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.