Abstract
In the rat auditory cortex, ventral (V) and posterodorsal (PD) areas are the two major auditory fields that receive thalamic afferents from the dorsal division (MGD) of the medial geniculate body. V and PD are presumed to serve distinct functions in tandem as the pair of major cortical recipients of extralemniscal thalamic inputs. To deduce the functional significance of V, efferent connections of V were examined with the anterograde tracer biocytin. V extends primarily in the ventral margin of area Te1. Biocytin was iontophoreticallcy injected into cortical regions, which were defined as V based on histological location, auditory response and thalamocortical connectivity. Anterograde labeling revealed two important aspects of cortical projections. First, V sent a projection to a well-confined region in the caudal end of the insular cortex (Ins) pivotal for fear memory formation during aversive conditioning. Second, V sent parallel projections to cortical regions that likely comprise the other non-primary auditory fields, including PD. The results suggest that V relays auditory input from the MGD to the Ins for affective memory formation and at the same time dispatches the auditory input, which could be weighed as emotional content, to the rest of non-primary auditory fields. PD is assumed to play a pivotal role in auditory spatial processing for directed attention. As the counterpart of PD, V is assumed to give rise to another major stream of cortical information processing most likely related to emotion. [J Physiol Sci. 2007;57 Suppl:S114]
