Sensory and multisensory representations within the cat rostral suprasylvian cortex.

Because the posterior limb of the rostral suprasylvian sulcus (RSp) of the cat resides in close proximity to representations of the somatosensory, auditory, and visual modalities, the surrounding cortices would be expected to be a region where a high degree of multisensory convergence and integration is found. The present experiments tested this notion by using anatomical and electrophysiological methods. Tracer injections into somatosensory, auditory, and visual cortical areas almost all produced terminal labeling within the RSp, albeit at different locations and in different proportions. Inputs from somatosensory cortices primarily targeted the inner portion of the anterior RSp; inputs from auditory cortices generally filled the outer portion of the middle and posterior RSp; inputs from visual cortices terminated in the inner portion of the posterior RSp. These projections did not have sharp borders but often overlapped one another, thereby providing a substrate for multisensory convergence. Electrophysiological recordings confirmed this anatomical organization as well as identifying the presence of multisensory (bimodal) neurons in the areas of overlap between representations. Curiously, however, the proportion of bimodal neurons was only 24% of the neurons sampled in this region, and the majority of these did not show multisensory interactions when combined-modality stimuli were presented. In summary, these experiments indicate that the RSp is primarily auditory in nature, but this representation could be further subdivided into an outer sulcal anterior auditory field (sAAF) and an inner field of the rostral suprasylvian sulcus (FRS).