More than 35 million Americans are over the age of 60 and the oldest-old represent the fastest growing segment of the population. More than 25 percent of the young-old and more than 60 percent of the oldest-old have impaired taste or smell. The underlying neural substrate is incompletely understood. Given the importance of nutrient intake to maintain good health and optimum function in old age, this is of great concern. A better understanding of chemosensory function in the elderly may suggest avenues for addressing age-related impairment. This project will take advantage of the power of the functional magnetic resonance imaging (fMRI) technique to image the aging brain while it is processing taste and odor stimulation in order to test the overarching hypothesis that functional changes in central nervous system activity, detectable in the cortical representation on fMRI, constitute a major neural substrate for chemosensory loss in aging. The focusing of this new technology on critical brain regions that are responsive to chemosensory inputs will address specific, critical questions regarding chemosensory aging: What are the brain areas that show changes in cortical activation in response to odor, to taste, and to multimodal odor and taste stimulation in the elderly? Are there common cortical substrates for aging of the olfactory and taste systems? Given that different cortical areas are expected to be activated in different chemosensory tasks (detection, identification, recall, recognition memory), are these areas differentially affected by aging? Do otherwise normal elderly persons who have the apolipoprotein E4 (Apo E4) allele show differential cortical activation during odor tasks? To address these questions, we have developed fMRI techniques and the stimulation paradigms necessary to present chemosensory stimuli in fMRI scanners. Neuroimaging is the only method capable of revealing precise spatial information about age-related differences in cortical response to chemosensory stimuli in living humans. We will correlate the results of fMRI with psychophysical assessment of taste and odor function in individual aging persons to provide an integrated understanding of brain/behavior functional relationships. The results of this project will deepen our understanding of changes in taste and odor processing in the aging brain in health and disease.
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