Connections of Auditory Medial Belt Cortex in Marmoset Monkeys

Abstract

The current working model of primate auditory cortex describes a centrally located core region, encompassed by a narrow belt region comprised of some seven putative subdivisions. The anatomical and physiological properties of the belt fields bordering the core medially, specifically RM and CM, represent the focus of the present study. Multiple injections of retrograde and bi-directional tracers were made into subdivisions of the medial belt, core, and lateral belt regions of auditory cortex in a marmoset monkey (Callithrix jacchus jacchus). Injection loci were confirmed by multiunit recordings and postmortem architectonic analyses. Local connections of the medial belt included subdivisions of the core, belt and parabelt regions. Rostral and caudal medial belt connections varied between rostral and caudal divisions of the medial belt with complete rostrocaudal labeling of the lateral belt. Local connections of the core included subdivisions of the core and belt regions. Injections to the lateral belt area ML labeled most of the core, belt and parabelt at all rostrocaudal levels. Injections into CM reveal a different thalamic pattern of label than RM. The findings are largely consistent with our working model of auditory cortex, and expand the model to reflect inputs to RM from rostral and caudal domains of the lateral belt and parabelt.