4.26 - The Representation of Flavor in the Brain

Abstract

Taste and olfactory cortical processing in primates (including humans) converges in the orbitofrontal cortex to form a representation of flavor. The orbitofrontal cortex contains the secondary taste and secondary olfactory cortical areas, and also higher cortical areas. Flavor representations are learned by olfactory-to-taste association learning in the orbitofrontal cortex. Oral texture (including viscosity and fat texture) is represented in the primary taste cortex, and is thus incorporated into flavor representations in the orbitofrontal cortex. Visual inputs reach the orbitofrontal cortex from the inferior temporal visual cortex, form learned associations with flavor representations, and thus allow visual inputs to guide food selection, and also to influence flavor perception. Cognitive inputs, such as a word description, can modulate flavor representations in the orbitofrontal cortex, and provide a mechanism for cognition to influence flavor. The orbitofrontal cortex is the first stage of processing in primates at which the reward value of taste and olfaction is represented, and activations in the human orbitofrontal cortex are correlated with subjective pleasantness ratings of taste, olfactory, and flavor stimuli. The orbitofrontal cortex connects with the amygdala and cingulate cortex, and in these regions there are also flavor representations. The conclusions are based on macaque neurophysiology and human functional neuroimaging. The aim of this chapter is to show how cortical taste and olfactory processing converges to form a representation of flavor. Much of the fundamental evidence relevant to humans comes from neuronal recording in nonhuman primates, and this is complemented by functional neuroimaging studies in humans.