[Functional MRI of the human brain responses to olfactory stimulation]

Image artifacts such as signal loss or distortion due to intravoxel phase dispersion at the skull base are problematic in analysis by functional MRI (fMRI). Since the olfactory center of the brain is located in the medial temporal and basal frontal areas, it is a challenge to try to detect the Blood Oxygenation Level Dependent (BOLD) effect during fMRI at olfactory stimulation. We examined 20 normal volunteers with a 1.5-T MR system, employing multishot, interleaved echo-planar imaging (EPI). Olfactory stimulation was performed with 2-methyl-1, 3-cyclo-pentanedione, a caramel-like fragrance, by presenting it for 20 seconds with two cycles of rest-stimulus paradigm. Sites of functional activation were identified by correlation analysis with a threshold of p < 0.01. Most commonly activated areas were the orbitofrontal and primary olfactory cortices. Mild activation was also observed in the cingulate gyrus, lateral temporal cortex, cerebellum, parietal and occipital lobes. These results indicate that olfactory stimulation participates in the emotion and behavior processes. Interestingly, broad activation in the "silent" area of the frontal and temporal lobe was also observed in some cases. Multishot EPI was a useful method to evaluate brain activation at the basal level on fMRI.