Functional organization of input from areas 17 and 18 to an extrastriate area in the cat

Abstract

In the cat, areas 17 and 18 have 2 main cortical targets: area 19 and a large region of suprasylvian cortex, referred to here as the Clare-Bishop area (Hubel and Wiesel, 1969). The functional organization of the latter area is not well understood. It seems likely that its organization reflects, in part, the organization of its inputs from areas 17 and 18, and I therefore studied the functional organization of these inputs. Responses were recorded directly from afferents terminating in the Clare-Bishop area after silencing its cells by local injections of kainic acid. Afferents were precisely ordered according to preferred orientation in a fashion resembling the columnar organization of area 17. Preferred direction was also an important organizing parameter. Within sizable regions of cortex, directional preference changed gradually or not at all, while at these regions' boundaries, preferred direction reversed by 180 degrees. Except for a loose grouping according to eye dominance, afferents were not ordered according to other response properties. It is possible that the afferent array is also compartmentalized according to the area of origin of each afferent. Inputs from areas 17 and 18, for example, might end in separate territories in the Clare-Bishop area. However, physiological recording, as well as anatomical experiments, failed to show a clear segregation. This study provides the first direct demonstration that a cortico-cortical pathway can be organized according to particular response properties. While the existence of an organization according to preferred orientation was not surprising, the high degree of order was unexpected. It is also interesting that afferents were well ordered according to 1 parameter, directional preference, that is weakly organized, at best, in area 17.