FMRI brain activation in response to odors is reduced in primary olfactory areas of elderly subjects.

Olfactory function is affected by aging and deficits often result in decreasing quality of life, health and safety. The present study investigated the cortical substrate of olfactory deficits related to aging with functional Magnetic Resonance Imaging (fMRI), with a retronasal olfactory stimulation protocol using flavored aqueous solutions presented to the mouth. Activation was found in young subjects in the piriform/amygdalar region and in the orbitofrontal cortex and in other areas previously found activated in neuroimaging studies using odorized air, including insula and cerebellum. Activation was seen in similar areas in old subjects but the degree of activation was significantly lower in regions receiving primary olfactory projections (piriform cortex, entorhinal cortex, and amygdala). This result supports the hypothesis of dysfunction and/or degeneration in areas critical to olfactory processing as a major cause of olfactory deficits in the older population.

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.