Rethinking the role of taste processing in insular cortex and forebrain circuits

Abstract

Over the years, many approaches towards studying the taste-responsive area of insular cortex have focused on how basic taste information is represented, and how lesions or silencing of this area impact taste-focused behaviors. Here, we review and highlight recent studies that imply that insular cortex does not contain a "primary" taste cortex in the traditional sense. Rather, taste is employed in concert with other internal and external sensory modalities by highly interconnected regions of insular cortex to guide ingestive decision-making, especially in context of estimating risk and reward. In rodent models, this may best be seen in context of foraging behaviors, which require flexibility and are dependent on learning and memory processes.

Keywords: behavior; circuit; cortex; feeding; foraging; taste.

Figure 1

Schematic representation of connectivity between major forebrain gustatory areas in regards to taste processing and feeding. The parabrachial nucleus (PBN) in the pons, which receives gustatory and visceral input directly from the medulla, is also shown as it is the source (in rodents) of divergent taste projections to the gustatory thalamus (GT) and central nucleus of the amygdala (CeA), as well as a relatively small projection to insular cortex (IC). In turn, PBN neurons are modulated by descending feedback from CeA and IC, but not GT. IC receives major inputs from GT and the basolateral amygdala (BLA), and projects heavily back to those areas. CeA itself does not project to IC, but communicates with BLA. BLA-IC reciprocal connectivity is directly implicated in the formation and expression of conditioned taste aversions (CTA). Other studies suggest that cortico-amygdalar outputs drive motivated, feeding-related behaviors, likely through striatal projections.