Visceral sensory input to the cerebral cortex and the basal ganglia

Vagal afferents monitor sensory events originating in the internal organs and convey the signals to the brain; this is an essential process of homeostatic regulation. Accordingly, vagal afferents and related brainstem nuclei have been studied with respect to autonomic regulation. By contrast, while vagal afferent activity diverges in the central nervous system and exerts a variety of influence on the brain functions, involvement of forebrain areas other than limbic or basal forebrain remains less understood. In this talk, cortical, thalamic and striatal representation of vagal afferents will be described. 1. Visceral information transmitted via vagal afferents ascends through a thalamocortical pathway parallel to the gustatory system. Input from the solitary tract nucleus (NTS) and / or the parabrachial nucleus (PB) arrive at the basal ventromedial thalamic nucleus, which in turn projects to both the insular and ventral sensorimotor cortex. These areas may qualify as the viscerosensory cortex. 2. Vagal afferents project to the thalamic parafascicular nucleus (Pf) via both NTS and PB. Since Pf vagal-responsive region massively projects to the striatum, this pathway would provide vagal input to the basal ganglia. Functional significance of these central projections can only be speculated at present. Vagal afferent activity contributes little to our conscious experience. These forebrain areas may work within the extended framework of autonomic regulation that includes behavioral adjustment of homeostatic needs, in part by affecting basic emotions. [J Physiol Sci. 2008;58 Suppl:S28]