Functional Magnetic Resonance Imaging Study of Human Olfaction and Normal Aging

Background. The function of human olfaction declines with advancing age. An important question centers on whether functional alterations to olfactory brain structures accompany age-related behavioral changes. In the present study, we tested the hypothesis that aged adults have intact though reduced activity in the central olfactory system using functional magnetic resonance imaging (fMRI). Methods. University of Pennsylvania Smell Identification Test (UPSIT) was used to test the smell function of 11 young (23.9 6 1.6 years) and 8 aged (66.4 6 4.4 years) healthy participants. Then, the participants received fMRI at 3.0 T with lavender and spearmint as stimulants. After fMRI, the participants provided ratings for the odorants ’ intensity and pleasantness. Results. The averageUPSIT score of the aged adults was 34.16 1.5, whichwas significantly lower than that of the young adults (37.36 1.1) (p .0004). Both age groups showed significant activation in major olfactory brain structures, including the primary olfactory cortex, entorhinal cortex, hippocampus and parahippocampal cortex, thalamus, hypothalamus, orbitofrontal cortex, and insular cortex and its extension into the inferior lateral frontal region. The aged adults showed less brain activity in olfactory structures (p .022), consistent with lower ratings of odor intensity and UPSIT scores. Activation intensity in bilateral primary olfactory cortex areas and right insular cortex was also comparatively weaker (p,.019). Conclusion. Results demonstrate that significant activation in aged adults can be observed in all the olfactory brai