Cortical Metabolic Arrangement During Olfactory Processing

Abstract

The aim of this article is to investigate the cortical metabolic arrangements in olfactory processing by using 18F 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 18F 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.

Evaluation of Task-Related Brain Activity: Is There a Role for18F FDG-PET Imaging?

“…A comparison of FDG uptake after a bolus injection at rest and during stimulation was performed in 11 normosmic subjects and reported, at rest, mainly increased glucose metabolism in left superior, inferior, middle, medial frontal, orbital gyri, and anterior cingulate cortex. Conversely, during olfactory stimulation PET imaging reported hyperactivation in the cuneus, lingual, and parahippocampal gyri, mainly in the left hemisphere [22, 23].…”

“…Therefore, authors considered rest as neutral olfactory stimulation in order to avoid olfactory pollution at rest and, after a month, compared to pure olfactory task activation scan. A comparison of FDG uptake after a bolus injection at rest and during stimulation has been performed [22].…”

“…Brodmann areas (BA) are usually identified at a range from 0 to 3 mm from the corrected Talairach coordinates of the SPM output isocenter by using a Talairach client available at http://www.talairach.org/index.html. As proposed by Bennett et al [33], SPM t-maps are usually corrected for multiple comparisons with the false discovery rate (P≤0.05) and corrected for multiple comparisons at the cluster level (P≤0.001)[22–25].…”

The Impact of COVID-19 Lockdown Measures and COVID-19 Infection on Cognitive Functions: A Review in Healthy and Neurological Populations

“…Interestingly, a recent report on a single case neuroimaging study with anosmia, due to COVID-19, revealed reduced metabolic activity in the orbitofrontal cortex, suggesting impaired neural function in this region [ 126 ]. It is well-known that the orbitofrontal cortex is responsible not only for the detection of common odors [ 127 ], but also for executive functions and attentional processing [ 128 , 129 , 130 ]. Thus, although future studies should elucidate this issue, the hypothesis might be advanced that, together with the lack of oxygen to the brain due to respiratory symptoms, executive functions and attentional deficits also arise as a consequence of abnormal activity in the orbitofrontal cortex.…”

A comprehensive review of imaging findings in COVID-19 - status in early 2021

“…An [ 18 F]-FDG-PET/CT examination was performed in a 27-year-old right-handed woman, who had been earlier diagnosed with COVID-19 by RT-PCR and suffered from isolated anosmia persisting for 6 weeks [ 233 ]. The scan showed pathological hypometabolism of the left orbitofrontal cortex [ 233 , 234 ], a region which receives projections from the primary olfactory cortex [ 235 , 236 ]. Hyposmia and anosmia due to CNS damage of other etiologies have previously been widely investigated by molecular imaging, especially in the context of Parkinson’s disease [ 237 – 239 ], where anosmia is an early presenting symptom.…”