Cortical representation of fat taste in human primary gustatory area: an fMRI mapping study

The representation of fat taste in the primary gustatory cortex (GI) of the fronto-parietal operculum was studied in 9 healthy subjects (8 right-handed; 4 women) by applying two taste stimuli (pure fat: rapeseed oil; salty: 1M NaCl) to either side of the tongue using a 5-min fMRI block design protocol approved by the local Ethics Committee. Data were analyzed with BrainVoyager software. Unilateral tongue stimulation with fat consistently evoked bilateral activation in area GI. Ipsilateral foci were generally larger and signal increases greater. Salty stimuli also evoked bilateral activation, as reported previously. Foci evoked by each tastant exhibited slightly but not significantly different mean Talairach coordinates, broad overlap and high individual variability; salty stimuli generally evoked more anterior and fatty stimuli more posterior foci. Consistent white matter activation was observed in the anterior callosal portion. These findings show that pure fat stimuli, e.g. rapeseed oil, activate area GI. Fat may therefore be considered as an additional primary taste. These data also confirm that gustatory pathways from tongue to cortex are bilaterally distributed with an ipsilateral predominance. However, a clear topographical organization could not be recognized, probably because the fMRI technique is unable to resolve fine topographical arrangements, or because the discriminative role of area GI for different tastants is based on different mechanisms, or both.