Different Neural Processing of Umami and Salty Taste Determined by Umami Identification Ability Independent of Repeated Umami Exposure.

There is a large inter-individual variation for umami taste perception. However the neural mechanism for this variability is not well understood. This study investigated brain responses to umami and salty taste among individuals with different umami identification abilities and the effect of repeated oral umami exposure on umami identification and neural processing of taste perceptions. Fifteen participants with high umami identification ability ("High Tasters, HT) and fifteen with low umami identification ability ("Low Tasters", LT) underwent three weeks of controlled exposure to umami taste (umami training). Prior to and after the training, participants underwent fMRI scans during which the umami taste solution and a control taste (salty) solution were delivered to their mouth using a gustometer. Taste intensity and pleasantness were rated after each scan. Umami taste identification was assessed before and after the umami training using "Taste Strips" test. Neuroimaging results showed different central processing of umami and salty taste based on umami identification ability, in which the umami LT had stronger activation in the thalamus and hippocampus while the umami HT showed stronger activation in the primary gustatory cortex. In addition, umami identification was significantly improved after umami training for LT. However, it was not reflected in changes in neural activation. The current study shows that attention and association/memory related brain structures play a significant role in the perception of umami taste; and with reference to the results of repeated umami exposure, the presence of very subtle changes regarding the neural processing.