Cortical Metabolic Arrangement During Olfactory Processing: Proposal for a 18F FDG PET/CT Methodological Approach

The aim of this article is to investigate the cortical metabolic arrangements in olfactory processing by using F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography. Twenty-six normosmic individuals (14 women and 12 men; mean age 46.7 +/- 10 years) were exposed to a neutral olfactory condition (NC) and, after 1 month, to a pure olfactory condition (OC) in a relatively ecological environment, that is, outside the scanner. All the subjects were injected with 185-210 megabecquerel of F-18 FDG during both stimulations. Statistical parametric mapping version 2 was used in order to assess differences between NC and OC. As a result, we found a significant higher glucose consumption during OC in the cuneus, lingual, and parahippocampal gyri, mainly in the left hemisphere. During NC, our results show a relative higher glucose metabolism in the left superior, inferior, middle, medial frontal, and orbital gyri as well as in the anterior cingulate cortex. The present investigation, performed with a widely available functional imaging clinical tool, may help to better understand the neural responses associated to olfactory processing in healthy individuals and in patients with olfactory disorders by acquiring data in an ecologic, noise-free, and resting condition in which possible cerebral activations related to unwanted attentional processes might be avoided.