An extensive intrinsic association fiber system within cat area 7 revealed by anterograde and retrograde axon tracing...

The associational connections within area 7 on the crown of the middle suprasylvian gyrus in adult cats were investigated with extracellular axon tracing techniques. Injections of wheat germ agglutinin conjugated to horseradish peroxidase or of 3H-proline into area 7 revealed the presence of widespread intrinsic connections that extend over the rostral to caudal extent of the middle suprasylvian gyrus (up to 10 mm in one direction from injection sites). The connections have a complex organization with cell bodies and particulate label concentrated in patches. The patches are irregular in shape and do not form any obvious pattern. Although the transported label is concentrated in patches, large numbers of retrogradely labeled cells and significant quantities of anterogradely transported label are found in the spaces between patches. The long associational connections originate from cells in layers 2-6 and project to all cortical layers. Pyramidal cells are the primary source of the projections.