Validation of a stimulation protocol suited to the investigation of odor-taste interactions with fMRI

A protocol suited to the investigations of odor-taste interactions in a functional magnetic resonance imaging (fMRI) scanner is described and results that confirm the validity of that protocol are presented. Stimuli were dissolved in water and presented to the mouth of the participant through plastic syringes and plastic tubes as 50 microl every 3 s for 18 s. Participants were lying on the back to simulate the conditions in a fMRI scanner and gave pleasantness and intensity ratings in response to each stimulus using a Labeled Magnitude Scale (LMS). Stimuli were three concentrations of two tastants (i.e., sucrose and NaCl) and two odorants [i.e., ethyl butyrate (fruity) and citral (citrus)] and all possible odor-taste mixtures. Results showed that additivity of intensity in odor-taste mixtures was linear and did not depend on the pleasantness of the mixture. This study showed the feasibility of acquiring reliable psychophysical data with a stimulation device compatible with the fMRI environment and provided the foundation for the interpretation of future fMRI investigations of odor-taste interactions in flavor.