Cortico-subcortical metabolic correlates of olfactory processing in healthy resting subjects

Abstract

A wide network of interconnected areas was previously found in neuroimaging studies involving normal as well as pathological subjects; however literature seems to suffer from a lack of investigation in glucose metabolism behaviour under olfactory condition. Thus, the present work describe for the first time a pure olfactory related brain response of metabolism by using 18F-fluorodeoxyglucose-Positron Emission Tomography/Computer Tomography in eleven resting subjects undergoing a neutral and a pure olfactory condition. By contrasting these experimental phases, it was possible to depict a re-organization pattern of default mode network structures in a relatively ecological environment. Moreover, by correlating such pattern with a battery of validated olfactory and neuropsychological tests, our work allowed in showing peculiar correlation data that could cluster the subjects sample in a certain range of normality. We believe the present study could integrate the current knowledge in olfactory research and could be a start-up for future contributions.

Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity

“…As previously reported (Alessandrini et al 2014a;Chiaravalloti et al 2015), the improved sensitivity of the state-of-the-art PET camera allowed to explore olfactory neural underpinnings in a defined ecologic condition, possibly avoiding cortical activation related to unwanted attentional processes and odor sensitivity enhancement (Å hs et al 2013). Upon the present experimental conditions PET studies might be considered the same way as a functional MRI (fMRI) study in which the temporal resolution is in the range of minutes instead of seconds (Scarmeas et al 2004).…”

“…According to previous studies of this research group (Alessandrini et al 2014a;Chiaravalloti et al 2015), all subjects underwent FDG-PET/CT after both a neutral (neutral condition-NC) and pure olfactory stimulation (olfactory condition-OC) by using a ordinary aerosol facial mask containing in its ampoule: only 5 ml of saline sodium chloride (NaCl) 0.9 % in NC and a solution of 1.5 ml of Vanilline 100 % (Dacor Ltd|Sarandrea Ltd) and 5 ml NaCl 0.9 % in OC.…”

“…A recent investigation reporting 18 F-2-fluoro-2-deoxy-Dglucose (FDG)-positron emission tomography (PET)/computer tomography (CT) cortical changes after a pure olfactory stimulation in MCS patients (Chiaravalloti et al 2015) demonstrated to overcome that possible unintended sensory stimulation (Alessandrini et al 2014a;Benjamin et al 2010;Hillert et al 2007;Orriols et al 2009, Azuma et al 2013Andersson et al 2014) related to such neuroimaging techniques coupling the olfactory task with the acquisition phase. These aspects could have constituted a possible common bias to the interpretation of the majority of existing data.…”

“…These aspects could have constituted a possible common bias to the interpretation of the majority of existing data. Thus, it remains unclear to what extent discrepancies in the results of different studies may reflect unwanted attentional behaviors, sensory-specific engagement of different brain regions rather than methodological discrepancies (Alessandrini et al 2014a).…”

“…The aim of the present study was to assess the sub-cortical metabolic changes related to a pure olfactory stimulation in resting MCS and healthy (HC) subjects by using a recently validated FDG-PET/CT technique (Alessandrini et al 2014a;Chiaravalloti et al 2015) with the purpose of depicting the neural patterns peculiar of MCS.…”