Interaction of gustatory and lingual somatosensory perceptions at the cortical level in the human: a functional magnetic resonance imaging study

The present study has investigated interaction at the cortical level in the human between two major components of flavor perception, pure chemical gus tatory and lingual somatosensory perception. Twelve subjects participated i n a functional magnetic resonance imaging study and tasted six stimuli, app lied on the whole tongue, among which four were pure gustatory stimuli (NaC l, aspartame, quinine and HCl, pH 2.4 or 2.2) and two were both taste and l ingual somatosensory stimuli, i.e. somato-gustatory stimuli (HCl, pH 1.6 or 1.5, and aluminum potassium sulfate). Functional images were acquired with an echo planar sequence on a 3 T system and were individually processed by correlation with the temporal perception profile. Both sets of stimuli sho wed activation in the same cortical areas, namely the insula, the rolandic operculum (base of the pre- and post-central gyri), the frontal operculum a nd the temporal operculum, confirming a wide overlap of taste and lingual s omatosensory representations. However, the relative activation across areas and the analysis of co-activated areas across all runs for each set of sti muli allowed discrimination of taste and somatosensory modalities. Factor a nalysis of correspondences indicated different patterns of activation acros s the sub-insular and opercular regions, depending on the gustatory or soma to-gustatory nature of the stimuli. For gustatory stimuli different activat ion patterns for the superior and inferior parts of the insula suggested a difference in function between these two insular sub-regions. Furthermore, the left inferior insula was co-activated with the left angular gyrus, a st ructure involved in semantic processing. In contrast, only somato-gustatory stimuli specifically produced a simultaneous and symmetrical activation of both the left and right rolandic opercula, which include a part of the sen sory homunculus dedicated to the tactile representation of oral structures.