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Cortex; a Journal Devoted To the Study... Aug 2023Lemon fragrance is known for its stimulating properties, but its mechanisms of action are not well known yet. This study aimed to examine the effect of lemon essential...
Lemon fragrance is known for its stimulating properties, but its mechanisms of action are not well known yet. This study aimed to examine the effect of lemon essential oil inhalation on healthy participants' alertness level and their neural correlates using magnetic resonance imaging (MRI). Twenty-one healthy men underwent functional MRI scans in different conditions: a resting state condition, a condition where they were exposed to passive lemon smelling (alternating exposure to lemon and breathing fresh air), and a control condition without lemon fragrance diffusion -the order of the last two conditions being randomized. Alertness levels were assessed immediately after each condition using the Karolinska Sleepiness Scale. Voxel-wise whole-brain global functional connectivity and graph theory analyses were computed to investigate brain functional connectivity and network topology alterations. After lemon fragrance inhalation, we observed a higher level of alertness as compared to resting state -but not compared to control condition. During lemon fragrance inhalation, we found increased global functional connectivity in the thalamus, paralleled by decreased global connectivity in several cortical regions such as precuneus, postcentral and precentral gyrus, lateral occipital cortex and paracingulate gyrus. Graph theory analysis revealed increased network integration in cortical regions typically involved in olfaction and emotion processing such as olfactory bulb, hypothalamus and thalamus, while decreased network segregation in several regions of the posterior part of the brain during olfaction as compared to resting state. The present findings suggest that lemon essential oil inhalation could increase the level of alertness.
Topics: Male; Humans; Brain; Brain Mapping; Magnetic Resonance Imaging; Attention; Thalamus
PubMed: 37285762
DOI: 10.1016/j.cortex.2023.04.012 -
European Archives of... Oct 2023In a previous neuroimaging study, patients with taste loss showed stronger activations in gustatory cortices compared to people with normal taste function during taste...
PURPOSE
In a previous neuroimaging study, patients with taste loss showed stronger activations in gustatory cortices compared to people with normal taste function during taste stimulations. The aim of the current study was to examine whether there are changes in central-nervous functional connectivity in patients with taste loss.
METHODS
We selected 26 pairs of brain regions related to taste processing as our regions of interests (ROIs). Functional magnetic resonance imaging (fMRI) was used to measure brain responses in seven patients with taste loss and 12 healthy controls as they received taste stimulations (taste condition) and water (water condition). The data were analysed using ROI-to-ROI functional connectivity analysis (FCA).
RESULTS
We observed weaker functional connectivity in the patient group between the left and right orbitofrontal cortex in the taste condition and between the left frontal pole and the left superior frontal gyrus in the water condition.
CONCLUSION
These results suggested that patients with taste loss experience changes of functional connectivity between brain regions not only relevant to taste processing but also to cognitive functions. While further studies are needed, fMRI might be helpful in diagnosing taste loss as an additional tool in exceptional cases.
Topics: Humans; Pilot Projects; Ageusia; Brain Mapping; Brain; Magnetic Resonance Imaging; Taste Disorders
PubMed: 37198301
DOI: 10.1007/s00405-023-08019-4 -
Rhinology Oct 2023Olfactory capacity increases during the period of ovulation, perhaps as an adjunct to mate selection; however, researchers have yet to elucidate the neural underpinning...
BACKGROUND
Olfactory capacity increases during the period of ovulation, perhaps as an adjunct to mate selection; however, researchers have yet to elucidate the neural underpinning of menstrual cycle-dependent variations in olfactory performance.
METHODOLOGY
A cohort of healthy volunteers (n = 88, grand cohort) underwent testing for gonadal hormone levels and resting-state functional magnetic resonance imaging with a focus on intrinsic functional connectivity (FC) in the olfactory network based on a priori seeds (piriform cortex and orbitofrontal cortex) during the periovulatory (POV) and menstrual (MEN) phases. A subcohort (n = 20, olfaction cohort) returned to the lab to undergo testing of olfactory performance during the POV and MEN phases of a subsequent menstrual cycle.
RESULTS
Olfactory performance and FC were both stronger in the periovulatory phase than in the menstrual phase. Enhanced FC was observed in the network targeting the cerebellum in both the grand and olfaction cohorts, while enhanced FC was observed in the middle temporal gyrus, lingual gyrus, dorsal medial prefrontal cortex, and postcentral gyrus in the grand cohort. Periovulatory progesterone levels in the grand cohort were positively correlated with FC in the network targeting the insula and paracentral lobule.
CONCLUSIONS
Our analysis revealed that superior olfactory function in the periovulatory period is associated with enhanced intrinsic connectivity in the olfactory network. These findings can be appreciated in the context of evolutionary biology.
Topics: Female; Humans; Smell; Menstrual Cycle; Magnetic Resonance Imaging; Brain
PubMed: 37000430
DOI: 10.4193/Rhin22.472 -
Journal of Neuroradiology = Journal de... Sep 2023Voxel-based morphometry (VBM) and surfaced-based morphometry (SBM) investigate the characteristics of gray matter (GM) in various diseases such as post-traumatic anosmia...
PURPOSE AND BACKGROUND
Voxel-based morphometry (VBM) and surfaced-based morphometry (SBM) investigate the characteristics of gray matter (GM) in various diseases such as post-traumatic anosmia (PTA). This study uses SBM and VBM to examine neuroanatomical measurements of GM and its functional correlates in patients with PTA.
METHODS
MRI images and olfactory test results were collected from 39 PTA patients and 39 healthy controls. Sniffin' Sticks test was used to assess olfactory function. GM structure was analyzed using CAT12 and FreeSurfer, and olfactory bulb (OB) volume and olfactory sulcus (OS) depth were calculated using 3D-Slicer.
RESULTS
Anosmic patients showed lower scores in the Sniffin' Sticks olfactory test, as well as reduction of OB volume and OS depth compared to control subjects. In these patients, overlapping changes were found between the VBM and SBM findings in the areas with significant effects, in particular, orbitofrontal cortex, superior and middle frontal gyrus, superior and middle temporal gyrus, anterior cingulate cortex, and insular cortex. Using SBM, decreased cortical thickness clusters were located in inferior and superior parietal gyrus. Further analysis in the region of interest demonstrated correlations between the orbitofrontal cortex and odor threshold score as well as the middle frontal gyrus and smell loss duration.
CONCLUSION
These findings show that the morphological alterations in the OB, OS, and the central olfactory pathways might contribute to the pathogenic mechanism of olfactory dysfunction after head injury.
Topics: Humans; Anosmia; Olfaction Disorders; Brain; Gray Matter; Gyrus Cinguli; Magnetic Resonance Imaging
PubMed: 36610937
DOI: 10.1016/j.neurad.2022.11.005