Functional Magnetic Resonance Imaging Research Of Regional Brain Responses To Pleasant And Unpleasant Odors

Purposes:Our goal was to use functional MRI(fMRI) to identify regional activation of the human cerebral cortex in response to pleasant and unpleasant odors.And to localize the olfactory centre and its tract and analyse the difference of activated brain region between the pleasant and unpleasant odor. We try to localize the mood and memory related brain region and analyse the response to mood stimulation.Material and methods: Twelve right-handed, healthy volunteers underwent this study. Two types of odors were given to them through the personally developed instrument.One was amyl?acetate ,which was regarded as pleasant odor ,and the unpleasant one was pyridine.We adopted block design in this experiment. MRI examination were performed on GE signa 1.5T echospeed MR/I, the raw fMRI data were dealed with Matlab 5.3, SPM99 and Talairach tool software.Results: Activation was present in the olfactory centre and important tract during administration of pleasant and unpleasant odors., such as uncus of hippocampus (BA 28),lateral medial nucleus of thalamus and orbitofrontal gyrus(BA11,BA47). The mood and memory related region were also found activated: medial frontal gyrus(BA 8), parahippocampal gyrus(BA 30,BA 34, 35, 36), cingulate gyrus (BA23,BA 29, 30, 31, 32), superior temporal gyrus and the superior, middle, inferior gyrus of right frontal lobe. Both of the two odors had more activation in the right hemisphere than the left. For example, the superior, middle, inferior gyrus of right frontal lobe, right orbitofrontal gyrus, right uncus of hippocampus and right lateral medial nucleus of thalamus were activated more prominently than the contralateral corresponding region.Further, it was found that the anterior part of the cerebrum was activated by the pleasant odor and that a more posterior part was activated by the unpleasant odor. To be exactly, the superior, middle, inferior gyrus of right frontal lobe, medial frontal gyrus and right insula lobe showed distinct activation induced by pleasant odor. And the anterior and middle part of cingulate gyrus were significantly activiated by pleasant odor, while the middle and posterior part of cingulate gyrus and bilateral parahippocampal gyrus were significantly activated by unpleasant odor. Otherwise, activation occurred in the brain stem and cerebellum during administration of unpleasant odor, which were not activated by pleasant odor.Conclusions: The uncus of hippocampus, lateral medial nucleus of thalamus and orbitofrontal gyrus are the olfactory centre and important tract. The medial frontal gyrus, parahippocampal gyrus, cingulate gyrus, superior temporal gyrus and the superior, middle, inferior gyrus of right frontal lobe are correlated with the mood stimulation. The dominant hemisphere of olfaction is the right hemisphere. The pleasant feeling is mainly concerned with the anterior part of the cerebrum, while the unpleasant feeling is involved in the posterior part of the cerebrum.