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Ageing Research Reviews Dec 2023In aging, olfactory deficits have been associated with lower cognition and motor function. Olfactory dysfunction is also one of the earliest features of... (Review)
Review
In aging, olfactory deficits have been associated with lower cognition and motor function. Olfactory dysfunction is also one of the earliest features of neurodegenerative disease. A comprehensive review of the neural correlates of olfactive function may reveal mechanisms underlying the associations among olfaction, cognition, motor function, and neurodegenerative diseases. Here, we summarize existing knowledge on the relationship between brain structural and functional measures and olfaction in older adults without and with cognitive impairment, including Alzheimer's disease. We identified 33 eligible studies (30 MRI/DTI,3 fMRI); 31 were cross-sectional, most assessed odor identification, and few examined multiple brain areas. Lower olfactory function was associated with smaller volumes in the temporal lobe (hippocampus,parahippocampal gyrus,fusiform gyrus), olfactory-related regions (piriform cortex,amygdala,entorhinal cortex), pre- and postcentral gyri, and globus pallidus. During aging, olfactory impairment may be associated with pathology in brain areas important for motor function and cognition, especially memory. Future longitudinal studies that include neuroimaging across different brain areas are warranted to determine the neurobiological changes underlying olfactory changes in the aging brain and the progression of neurodegeneration.
Topics: Humans; Aged; Neurodegenerative Diseases; Brain; Entorhinal Cortex; Hippocampus; Temporal Lobe; Magnetic Resonance Imaging; Cognitive Dysfunction
PubMed: 37913831
DOI: 10.1016/j.arr.2023.102095 -
Behavioral and Brain Functions : BBF Dec 2023Parosmia is a qualitative olfactory dysfunction presenting as "distorted odor perception" in presence of an odor source. Aim of this study was to use resting state...
OBJECTIVE
Parosmia is a qualitative olfactory dysfunction presenting as "distorted odor perception" in presence of an odor source. Aim of this study was to use resting state functional connectivity to gain more information on the alteration of olfactory processing at the level of the central nervous system level.
METHODS
A cross sectional study was performed in 145 patients with parosmia (age range 20-76 years; 90 women). Presence and degree of parosmia was diagnosed on the basis of standardized questionnaires. Participants also received olfactory testing using the "Sniffin' Sticks". Then they underwent resting state scans using a 3 T magnetic resonance imaging scanner while fixating on a cross.
RESULTS
Whole brain analyses revealed reduced functional connectivity in salience as well as executive control networks. Region of interest-based analyses also supported reduced functional connectivity measures between primary and secondary olfactory eloquent areas (temporal pole, supramarginal gyrus and right orbitofrontal cortex; dorso-lateral pre-frontal cortex and the right piriform cortex).
CONCLUSIONS
Participants with parosmia exhibited a reduced information flow between memory, decision making centers, and primary and secondary olfactory areas.
Topics: Humans; Female; Young Adult; Adult; Middle Aged; Aged; Cross-Sectional Studies; Olfaction Disorders; Smell; Brain; Magnetic Resonance Imaging
PubMed: 38115149
DOI: 10.1186/s12993-023-00225-8 -
Annals of Clinical and Translational... Dec 2023To investigate structural and functional connectivity changes in brain olfactory-related structures in a longitudinal prospective cohort of isolated REM sleep behavior...
OBJECTIVE
To investigate structural and functional connectivity changes in brain olfactory-related structures in a longitudinal prospective cohort of isolated REM sleep behavior disorder (iRBD) and their clinical correlations, longitudinal evolution, and predictive values for phenoconversion to overt synucleinopathies, especially Lewy body diseases.
METHODS
The cohort included polysomnography-confirmed iRBD patients and controls. Participants underwent baseline assessments including olfactory tests, neuropsychological evaluations, the Movement Disorders Society-Unified Parkinson's Disease Rating Scale, 3T brain MRI, and F-FP-CIT PET scans. Voxel-based morphometry (VBM) was performed to identify regions of atrophy in iRBD, and volumes of relevant olfactory-related regions of interest (ROI) were estimated. Subgroups of patients underwent repeated volumetric MRI and resting-state functional MRI (fMRI) scans after four years.
RESULTS
A total of 51 iRBD patients were included, with 20 of them converting to synucleinopathy (mean time to conversion 3.08 years). Baseline VBM analysis revealed atrophy in the right olfactory cortex and gyrus rectus in iRBD. Subsequent ROI comparisons with controls showed atrophy in the amygdala. These olfactory-related atrophies tended to be associated with worse depression, anxiety, and urinary problems in iRBD. Amygdala F-FP-CIT uptake tended to be reduced in iRBD patients with hyposmia (nonsignificant after multiple comparison correction) and correlated with urinary problems. Resting-state fMRI of 23 patients and 32 controls revealed multiple clusters with aberrant olfactory-related functional connectivity. Hypoconnectivity between the putamen and olfactory cortex was associated with mild parkinsonian signs in iRBD. Longitudinal analysis of volumetric volumetric MRI in 22 iRBD patients demonstrated four-year progression of olfactory-related atrophy. Cox regression analysis revealed that this atrophy significantly predicted phenoconversion.
INTERPRETATION
Progressive atrophy of central olfactory structures may be a potential indicator of Lewy body disease progression in iRBD.
Topics: Humans; REM Sleep Behavior Disorder; Prospective Studies; Tropanes; Brain; Lewy Body Disease; Synucleinopathies
PubMed: 37743764
DOI: 10.1002/acn3.51905 -
Frontiers in Neuroscience 2023
PubMed: 38249580
DOI: 10.3389/fnins.2023.1307844 -
Neural Regeneration Research Jan 2024Adult neurogenesis, the process of creating new neurons, involves the coordinated division, migration, and differentiation of neural stem cells. This process is... (Review)
Review
Adult neurogenesis, the process of creating new neurons, involves the coordinated division, migration, and differentiation of neural stem cells. This process is restricted to neurogenic niches located in two distinct areas of the brain: the subgranular zone of the dentate gyrus of the hippocampus and the subventricular zone of the lateral ventricle, where new neurons are generated and then migrate to the olfactory bulb. Neurogenesis has been thought to occur only during the embryonic and early postnatal stages and to decline with age due to a continuous depletion of neural stem cells. Interestingly, recent years have seen tremendous progress in our understanding of adult brain neurogenesis, bridging the knowledge gap between embryonic and adult neurogenesis. Here, we discuss the current status of adult brain neurogenesis in light of what we know about neural stem cells. In this notion, we talk about the importance of intracellular signaling molecules in mobilizing endogenous neural stem cell proliferation. Based on the current understanding, we can declare that these molecules play a role in targeting neurogenesis in the mature brain. However, to achieve this goal, we need to avoid the undesired proliferation of neural stem cells by controlling the necessary checkpoints, which can lead to tumorigenesis and prove to be a curse instead of a blessing or hope.
PubMed: 37488837
DOI: 10.4103/1673-5374.375317 -
Acta Radiologica (Stockholm, Sweden :... Sep 2023Bipolar disorder (BD) is a mental health disorder.
BACKGROUND
Bipolar disorder (BD) is a mental health disorder.
PURPOSE
To investigate the peripheric and central olfactory measurements in patients with BD using magnetic resonance imaging (MRI).
MATERIAL AND METHODS
This study was conducted retrospectively. Group 1 consisted of 27 euthymic patients with BD (14 men, 13 women) and Group 2 consisted of 27 healthy controls (14 men, 13 women). Olfactory bulb (OB) volume and olfactory sulcus (OS) depth (peripheric), and corpus amygdala and insular gyrus area (central) measurements were performed using cranial MRI.
RESULTS
OB volume and OS depth value of the bipolar group were lower than the control group, but there were no significant differences between the groups ( > 0.05). The corpus amygdala and left insular gyrus area of the bipolar group were significantly lower than those in the control group ( < 0.05). There were positive correlations between OB volumes and OS depths, the insular gyrus areas, and the corpus amygdala areas ( < 0.05). As the number of depressive episodes and duration of illness increased in bipolar patients, the depth of the sulcus decreased ( < 0.05).
CONCLUSION
In the present study a correlation was detected between OB volumes and the structures, known as emotional processing (e.g. insular gyrus area, corpus amygdala), and clinical features. Accordingly, new treatment techniques, such as olfactory training, may be considered an option in the treatment of such patients with BD.
Topics: Male; Humans; Female; Bipolar Disorder; Olfaction Disorders; Retrospective Studies; Smell; Amygdala; Magnetic Resonance Imaging
PubMed: 37312533
DOI: 10.1177/02841851231179174 -
The Journal of Clinical Endocrinology... Feb 2024To investigate the brain structural and functional alterations in patients with thyroid-associated ophthalmopathy (TAO) before and after glucocorticoid therapy, using...
OBJECTIVE
To investigate the brain structural and functional alterations in patients with thyroid-associated ophthalmopathy (TAO) before and after glucocorticoid therapy, using voxel-based morphometry (VBM) as well as resting-state functional magnetic resonance imaging (MRI) with amplitude of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo).
METHODS
Between 2019 and 2022, 32 patients with TAO and 23 healthy controls underwent pre-therapy MRI in Nanjing, China. Intravenous glucocorticoid therapy was administered to all patients. At 3 months after end of therapy, 26 patients were available for rescanned MRI. VBM, ALFF, and ReHo were used to evaluate the brain structural and functional differences.
RESULTS
Before therapy, TAO patients showed significantly decreased gray matter volume (GMV) in the left orbital part of superior frontal gyrus (ORBsup) and medial superior frontal gyrus (SFGmed) than healthy controls. Patients had higher ALFF values in bilateral gyrus rectus and olfactory cortex and lower values in bilateral cuneus. Patients also showed decreased ReHo values in bilateral lingual gyrus. After therapy, increased GMV in the left anterior cingulate gyrus and SFGmed, increased ALFF values in bilateral cuneus and superior occipital gyrus, and increased ReHo values in bilateral SFGmed were found in TAO patients compared to the pre-therapy cohort. Compared to controls, decreased GMV in left ORBsup was observed in post-therapy TAO patients.
CONCLUSION
Our results indicated that TAO might cause functional and structural deficits in the visual and emotional regions of the brain, with recovery in the former and partial restoration in the latter after effective glucocorticoid therapy. These findings may lead to deeper understanding of the pathophysiological mechanism behind TAO.
Topics: Humans; Glucocorticoids; Graves Ophthalmopathy; Brain; Gray Matter; Brain Mapping; Magnetic Resonance Imaging
PubMed: 37864850
DOI: 10.1210/clinem/dgad626