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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 -
Journal of Clinical Neuroscience :... Sep 2020Since the outbreak with novel corona virus in December 2019, a myriad of different neurological manifestations in patients with COVID-19 infection have been reported. We...
Since the outbreak with novel corona virus in December 2019, a myriad of different neurological manifestations in patients with COVID-19 infection have been reported. We present a case of non-traumatic intracranial hemorrhage in the olfactory gyrus in a patient who tested positive for SARS-COV-2. The area of hemorrhage is not a common location for spontaneous hemorrhage. Given that loss of smell is considered a relatively common symptom of this pandemic, it is an intriguing association of COVID-19 and olfactory gyrus ICH for neurotropism of SARS-CoV2 for olfactory bulb and glia cells through nasal mucosa. Future studies will need to elucidate the exact mechanism of anosmia from COVID-19 and potential mechanisms leading to ICH.
Topics: Betacoronavirus; COVID-19; Cerebral Hemorrhage; Coronavirus Infections; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Olfaction Disorders; Pandemics; Parietal Lobe; Pneumonia, Viral; SARS-CoV-2; Smell
PubMed: 33070912
DOI: 10.1016/j.jocn.2020.07.033 -
Nature Apr 2022There is strong evidence of brain-related abnormalities in COVID-19. However, it remains unknown whether the impact of SARS-CoV-2 infection can be detected in milder...
There is strong evidence of brain-related abnormalities in COVID-19. However, it remains unknown whether the impact of SARS-CoV-2 infection can be detected in milder cases, and whether this can reveal possible mechanisms contributing to brain pathology. Here we investigated brain changes in 785 participants of UK Biobank (aged 51-81 years) who were imaged twice using magnetic resonance imaging, including 401 cases who tested positive for infection with SARS-CoV-2 between their two scans-with 141 days on average separating their diagnosis and the second scan-as well as 384 controls. The availability of pre-infection imaging data reduces the likelihood of pre-existing risk factors being misinterpreted as disease effects. We identified significant longitudinal effects when comparing the two groups, including (1) a greater reduction in grey matter thickness and tissue contrast in the orbitofrontal cortex and parahippocampal gyrus; (2) greater changes in markers of tissue damage in regions that are functionally connected to the primary olfactory cortex; and (3) a greater reduction in global brain size in the SARS-CoV-2 cases. The participants who were infected with SARS-CoV-2 also showed on average a greater cognitive decline between the two time points. Importantly, these imaging and cognitive longitudinal effects were still observed after excluding the 15 patients who had been hospitalised. These mainly limbic brain imaging results may be the in vivo hallmarks of a degenerative spread of the disease through olfactory pathways, of neuroinflammatory events, or of the loss of sensory input due to anosmia. Whether this deleterious effect can be partially reversed, or whether these effects will persist in the long term, remains to be investigated with additional follow-up.
Topics: Aged; Aged, 80 and over; Biological Specimen Banks; Brain; COVID-19; Humans; Magnetic Resonance Imaging; Middle Aged; SARS-CoV-2; Smell; United Kingdom
PubMed: 35255491
DOI: 10.1038/s41586-022-04569-5 -
Neuroscience Dec 2019The production of new neurons and their incorporation into preexisting neuronal circuits occur throughout adulthood in the olfactory bulb and the hippocampal dentate...
The production of new neurons and their incorporation into preexisting neuronal circuits occur throughout adulthood in the olfactory bulb and the hippocampal dentate gyrus of the mammalian brain. To determine whether the adult-born neurons are engaged in the acquisition and retrieval of olfactory associative memory, we developed and validated a single-trial olfactory fear conditioning protocol in mice which allows to detect activation of newborn neurons during a specific episode of memory acquisition. Using c-Fos mapping of neuronal activity, we then examined the activation of new and preexisting neurons during training and testing sessions. We found that a single trial of olfactory fear conditioning did not lead to a significant increase in the number of c-Fos-positive granule cells (GCs) of the olfactory bulb and the dentate gyrus. However, the activity of these two cell populations was dramatically increased during memory retrieval. Activation of neurons in the dentate gyrus during memory retrieval was observed mainly in the suprapyramidal blade. In the olfactory bulb, 1.6-2.7% of newborn GCs marked with thymidine analogues (2, 4, and 6 weeks old) expressed c-Fos during memory retrieval, while in the dentate gyrus no newborn neurons were found among the c-Fos-positive cells. These data are consistent with the hypothesis that adult-born GCs of the olfactory bulb are less involved in odor-cued associative fear memory than in odor-cued operant behavior memory.
Topics: Animals; Conditioning, Psychological; Dentate Gyrus; Fear; Male; Memory; Mental Recall; Mice; Neurogenesis; Neurons; Olfactory Bulb; Olfactory Perception; Proto-Oncogene Proteins c-fos
PubMed: 31672642
DOI: 10.1016/j.neuroscience.2019.09.012 -
Frontiers in Neuroscience 2014Neurogenesis continues well beyond embryonic and early postnatal ages in three areas of the nervous system. The subgranular zone supplies new neurons to the dentate... (Review)
Review
Neurogenesis continues well beyond embryonic and early postnatal ages in three areas of the nervous system. The subgranular zone supplies new neurons to the dentate gyrus of the hippocampus. The subventricular zone supplies new interneurons to the olfactory bulb, and the olfactory neuroepithelia generate new excitatory sensory neurons that send their axons to the olfactory bulb. The latter two areas are of particular interest as they contribute new neurons to both ends of a first-level circuit governing olfactory perception. The vomeronasal organ and the main olfactory epithelium comprise the primary peripheral olfactory epithelia. These anatomically distinct areas share common features, as each exhibits extensive neurogenesis well beyond the juvenile phase of development. Here we will discuss the effect of age on the structural and functional significance of neurogenesis in the vomeronasal and olfactory epithelia, from juvenile to advanced adult ages, in several common model systems. We will next discuss how age affects the regenerative capacity of these neural stem cells in response to injury. Finally, we will consider the integration of newborn neurons into an existing circuit as it is modified by the age of the animal.
PubMed: 25018692
DOI: 10.3389/fnins.2014.00182 -
Neurology Jul 1998Olfactory epileptic auras are rare, constituting about 0.9% of all auras, and are typically described as unpleasant. They have usually been associated with tumors, but...
BACKGROUND
Olfactory epileptic auras are rare, constituting about 0.9% of all auras, and are typically described as unpleasant. They have usually been associated with tumors, but in some recent studies they have not.
METHODS
We identified 13 patients (7 male, 6 female) with olfactory epileptic auras from 1423 patients with partial epilepsy evaluated for intractable seizures between 1991 and 1996. All had routine EEGs and MRI. Twelve underwent prolonged video-EEG monitoring.
RESULTS
Olfactory sensations were of various types but unpleasant in only seven. Auras evolved to complex partial seizures (automotor, hypermotor, or dialeptic seizures) in 12 patients, with further evolution to generalized tonic-clonic seizures in three and aphasic seizures in one patient. The EEG focus was localized to the mesial temporal region in all. Ten patients had a mesial temporal tumor; in one patient, it extended to the superior temporal gyrus, and in another, the frontal lobe. The tumor involved only the amygdala in two patients and both amygdala and hippocampus in six; none had hippocampal involvement alone. Surgery was performed in nine patients. All except one with partial tumor resection had a seizure-free outcome. This patient also became seizure-free after repeat surgery to remove residual tumor tissue in the amygdala.
CONCLUSIONS
Olfactory auras are not necessarily unpleasant. The amygdala is the most likely symptomatogenic zone of olfactory auras. Tumors are the commonest etiology; mesial temporal sclerosis is a relatively rare cause.
Topics: Adolescent; Adult; Child; Child, Preschool; Electroencephalography; Epilepsy, Temporal Lobe; Female; Hallucinations; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Odorants; Smell
PubMed: 9674778
DOI: 10.1212/wnl.51.1.56 -
Neuropathology and Applied Neurobiology Dec 2017Alzheimer's disease (AD) is characterized by cholinergic dysfunction and deposition of β-amyloid (Aβ) plaques and tau neurofibrillary tangles (NFTs) in the brain....
AIMS
Alzheimer's disease (AD) is characterized by cholinergic dysfunction and deposition of β-amyloid (Aβ) plaques and tau neurofibrillary tangles (NFTs) in the brain. Olfactory abnormalities often precede cognitive symptoms in AD, indicating early involvement of pathology in olfactory structures. The cholinergic system is important not only in cognition but also in modulation of the olfactory system. The primary olfactory gyrus (POG) is comprised of the olfactory tract, anterior olfactory nucleus (AON) and olfactory area (OA). Because of the importance of the olfactory and cholinergic systems, we examined the anatomical and cholinergic organization of the POG in normal human brain and neuropathology in AD.
METHODS
Cytoarchitecture of the POG was studied using Nissl staining in normal (n = 8) and AD (n = 6) brains. Distributions of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) were determined using histochemical methods. Aβ plaques and tau NFTs were detected using immunohistochemistry. Abundance of AD pathology was assessed using a semi-quantitative approach.
RESULT
Nissl staining showed pyramidal cells in the AON and paleocortical organization of the OA. AChE stained neurons and neuropil in the AON and OA, while BChE activity was noted in the olfactory tract and in AON and OA neurons. Pathology was frequent in the AD POG and the abundance of BChE-associated AD pathology was greater than that associated with AChE.
CONCLUSIONS
AChE and BChE activities in normal POG recapitulated their distributions in other cortical regions. Greater abundance of BChE-associated, in comparison to AChE-associated, AD pathology in the POG suggests preferential involvement of BChE in olfactory dysfunction in AD.
Topics: Acetylcholinesterase; Aged; Aged, 80 and over; Alzheimer Disease; Butyrylcholinesterase; Cholinergic Neurons; Female; Humans; Male; Middle Aged; Neurofibrillary Tangles; Olfactory Cortex; Plaque, Amyloid
PubMed: 28644906
DOI: 10.1111/nan.12423 -
PloS One 2023
Expression of Concern: Stimulation of the Sigma-1 Receptor by DHEA Enhances Synaptic Efficacy and Neurogenesis in the Hippocampal Dentate Gyrus of Olfactory Bulbectomized Mice.
PubMed: 37582118
DOI: 10.1371/journal.pone.0290363 -
Scientific Reports Aug 2021Removing function from a developed and functional sensory system is known to alter both cerebral morphology and functional connections. To date, a majority of studies...
Removing function from a developed and functional sensory system is known to alter both cerebral morphology and functional connections. To date, a majority of studies assessing sensory-dependent plasticity have focused on effects from either early onset or long-term sensory loss and little is known how the recent sensory loss affects the human brain. With the aim of determining how recent sensory loss affects cerebral morphology and functional connectivity, we assessed differences between individuals with acquired olfactory loss (duration 7-36 months) and matched healthy controls in their grey matter volume, using multivariate pattern analyses, and functional connectivity, using dynamic connectivity analyses, within and from the olfactory cortex. Our results demonstrate that acquired olfactory loss is associated with altered grey matter volume in, among others, posterior piriform cortex, a core olfactory processing area, as well as the inferior frontal gyrus and angular gyrus. In addition, compared to controls, individuals with acquired anosmia displayed significantly stronger dynamic functional connectivity from the posterior piriform cortex to, among others, the angular gyrus, a known multisensory integration area. When assessing differences in dynamic functional connectivity from the angular gyrus, individuals with acquired anosmia had stronger connectivity from the angular gyrus to areas primary responsible for basic visual processing. These results demonstrate that recently acquired sensory loss is associated with both changed cerebral morphology within core olfactory areas and increase dynamic functional connectivity from olfactory cortex to cerebral areas processing multisensory integration.
Topics: Aged; Anosmia; Brain; Brain Mapping; Case-Control Studies; Female; Gray Matter; Humans; Male; Middle Aged; Support Vector Machine
PubMed: 34385571
DOI: 10.1038/s41598-021-95968-7