FUNCTIONAL MR-IMAGING DURING ODOR STIMULATION - PRELIMINARY DATA

PURPOSE: To determine the locations and extent of activation in areas of the brain at functional magnetic resonance (MR) imaging with olfact ory stimulation and to determine whether accommodation or amplificatio n of brain activation occurs with sequential olfactory stimulation. MA TERIALS AND METHODS: Five adult men with normal senses of smell underw ent multisection, gradient-echo, echo-planar imaging according to a bl ood-oxygen-level-dependent experimental paradigm. Odorants that nearly exclusively stimulate the olfactory system and odorants that stimulat e the olfactory and trigeminal nerves were compared by using repetitiv e imaging procedures. RESULTS: Activation with olfactory nerve-mediate d odorants was demonstrated in the orbitofrontal cortex (Brodmann area 11) with a right-sided predominance; Mild cerebellar stimulation was also observed. With repeated testing, overall activation with olfactor y nerve-mediated odorants declined: Odorants that also stimulated the trigeminal nerve produced additional cingulate, temporal, cerebellar, and occipital activation. Activation with combined trigeminal and olfa ctory system odors increased more-than sixfold with repeated testing. CONCLUSION: Olfactory nerve-mediated and combined olfactory and trigem inal nerve-mediated odorants activate different regions of the brain. Orbitofrontal stimulation spreads to all parts of the brain when a tri geminal component is added. Habituation (deactivation) occurs with rep eated testing of olfactory nerve-mediated odorants, while, paradoxical ly, activation increases with repeated exposure to odors that also sti mulate the trigeminal nerve.