Unlike visual or tactile perception, the functional anatomy of odor perception in humans has received very limited attention. This is unfortunate because the brain regions involved in odor perception appear to overlap with the brain regions involved in motivation and emotion. Since, in alcoholics, states of craving for alcohol can be induced by the odor of alcoholic beverages and these states involve both motivational and emotional components, we felt, as a prelude to studies of the functional neuroanatomy of alcohol craving, it would be important to develop techniques to examine brain changes associated with olfactory perception. Normal volunteers were exposed to various odorants using a continuous airflow system, while lying in a standard 1.5 Tesla MRI scanner. A pulse sequence developed at the In Vivo NMR Center was used to image blood volume under controlled conditions. Most foci of signal intensity change were located in secondary olfactory areas, such as amygdala, entorhinal cortex, nucleus accumbens/septal nuclei, and some in orbital frontal cortex. Different sites of changes were found in different subjects, possibly due to the relatively low sensitivity of this novel brain imaging method. However only 25% of normal subjects show significant changes in signal intensity. For this reason it was felt that fMRI at present does not have sufficient power to image brain response to odors. 15-0 PET appears to hold greater promise for imaging effects of olfactory stimulation. scans during olfactory stimulation in order to compare the distribution of changes in cerebral blood flow measured during PET in both alcoholics and controls. Controls demonstrate a significant increase in cerebral blood flow during exposure to the odor of alcohol containing beverages in primary and secondary olfactory cortex. In contrast, alcoholics show less robust activation in primary and secondary olfactory cortex during exposure to the odor of alcohol containing beverages. These results are consistent with a hyporesponsivity of limbic brain regions among alcoholics.
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