Gustation and Olfaction: The Importance of Place and Time

Abstract

Animals can smell odors from the external environment or from their mouth via two routes: orthonasal and retronasal, respectively. Little is known about how the brain processes orthonasal and retronasal odors associated with taste, but a new study has revealed an important role for the gustatory cortex in such odor processing.

Figure 1.. Gustatory cortex engagement in different odor–taste paradigms.

(A) Schematic sagittal section of the mouse head (left) depicting simultaneous presentation of orthonasal odor and taste (t₀). In this issue of Current Biology, Blankenship et al. [2] report that associations between orthonasal odors and taste are slower to establish than associations between retronasal odors and taste. In addition, they demonstrate that the gustatory cortex is not necessary for the expression of an odor preference following association between an orthonasal odor and saccharin (right: coronal section featuring gustatory cortex, GC). (B) The gustatory cortex is necessary for the expression of a preference developed with the simultaneous presentation of retronasal odor and taste. (C) Organisms can learn pairings when orthonasal odors precede (t₀) taste (t₁) and activity in gustatory cortex is recruited. The extent to which timing and route of odor exposure interact with taste and the circumstances in which gustatory cortex is necessary have yet to be exhaustively studied. We hypothesize that the gustatory cortex will play a causal role in the expression of these associations, based on prior studies on the involvement of gustatory cortex in mediating behaviors triggered by predictive cues.