The organization of the ipsilateral corticocortical projections of the middle sylvian gyrus (AII) in the cat cerebral cortex: an anterograde and retrograde tracing study

Abstract

The primary auditory area and surrounding cortical areas including the secondary auditory area subserve auditory information processing. In this study, corticocortical ipsilateral connections of the secondary auditory area were investigated in the cat by injections of axonally transported tracers into this area. Retrogradely labeled cells and anterogradely labeled terminals were observed within the secondary auditory area itself, and the primary, posterior, and ventroposterior auditory areas, in the insular cortex and in the temporal auditory area. These labeled terminals appeared in patches or bands. In the ventroposterior auditory area, a transverse band of anterograde and retrograde labeling, which extended from the posterior ectosylvian sulcus to the surface of the posterior ectosylvian gyrus was observed. In addition, scattered labeling was detected in the posterior auditory area. Although different parts of the secondary auditory area were found to send axons to different zones within the temporal cortex, no precise topographical arrangement was detected. When two different tracers were injected into the secondary auditory area and the anterior auditory area, respectively, some terminal aggregates anterogradely labeled from these two areas converged within the posterior auditory area. The organization of these connections is discussed in relationship to the functional role of the auditory cortical areas. © 1998 Elsevier Science Inc.