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Neuropsychology Review Mar 2024Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating... (Review)
Review
Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating olfactory functioning. Declines in olfaction parallel declines in cognition in various pathological conditions and aging. Research suggests a dynamic neural connection exists between olfaction and cognition. Thus, if OT can improve olfaction, could OT also improve cognition and support brain function? To answer this question, we conducted a systematic review of the literature to determine whether there is evidence that OT translates to improved cognition or altered brain morphology and connectivity that supports cognition. Across three databases (MEDLINE, Scopus, & Embase), 18 articles were identified in this systematic review. Overall, the reviewed studies provided emerging evidence that OT is associated with improved global cognition, and in particular, verbal fluency and verbal learning/memory. OT is also associated with increases in the volume/size of olfactory-related brain regions, including the olfactory bulb and hippocampus, and altered functional connectivity. Interestingly, these positive effects were not limited to patients with smell loss (i.e., hyposmia & anosmia) but normosmic (i.e., normal ability to smell) participants benefitted as well. Implications for practice and research are provided.
Topics: Humans; Brain; Cognition; Olfaction Disorders; Olfactory Training; Smell
PubMed: 36725781
DOI: 10.1007/s11065-022-09573-0 -
Physiological Reviews Oct 2023Anosmia, the loss of the sense of smell, is one of the main neurological manifestations of COVID-19. Although the SARS-CoV-2 virus targets the nasal olfactory... (Review)
Review
Anosmia, the loss of the sense of smell, is one of the main neurological manifestations of COVID-19. Although the SARS-CoV-2 virus targets the nasal olfactory epithelium, current evidence suggests that neuronal infection is extremely rare in both the olfactory periphery and the brain, prompting the need for mechanistic models that can explain the widespread anosmia in COVID-19 patients. Starting from work identifying the non-neuronal cell types that are infected by SARS-CoV-2 in the olfactory system, we review the effects of infection of these supportive cells in the olfactory epithelium and in the brain and posit the downstream mechanisms through which sense of smell is impaired in COVID-19 patients. We propose that indirect mechanisms contribute to altered olfactory system function in COVID-19-associated anosmia, as opposed to neuronal infection or neuroinvasion into the brain. Such indirect mechanisms include tissue damage, inflammatory responses through immune cell infiltration or systemic circulation of cytokines, and downregulation of odorant receptor genes in olfactory sensory neurons in response to local and systemic signals. We also highlight key unresolved questions raised by recent findings.
Topics: Anosmia; Humans; COVID-19; Olfactory Receptor Neurons; Animals; SARS-CoV-2
PubMed: 37342077
DOI: 10.1152/physrev.00012.2023 -
Neuroinvasion and anosmia are independent phenomena upon infection with SARS-CoV-2 and its variants.Nature Communications Jul 2023Anosmia was identified as a hallmark of COVID-19 early in the pandemic, however, with the emergence of variants of concern, the clinical profile induced by SARS-CoV-2...
Anosmia was identified as a hallmark of COVID-19 early in the pandemic, however, with the emergence of variants of concern, the clinical profile induced by SARS-CoV-2 infection has changed, with anosmia being less frequent. Here, we assessed the clinical, olfactory and neuroinflammatory conditions of golden hamsters infected with the original Wuhan SARS-CoV-2 strain, its isogenic ORF7-deletion mutant and three variants: Gamma, Delta, and Omicron/BA.1. We show that infected animals develop a variant-dependent clinical disease including anosmia, and that the ORF7 of SARS-CoV-2 contributes to the induction of olfactory dysfunction. Conversely, all SARS-CoV-2 variants are neuroinvasive, regardless of the clinical presentation they induce. Taken together, this confirms that neuroinvasion and anosmia are independent phenomena upon SARS-CoV-2 infection. Using newly generated nanoluciferase-expressing SARS-CoV-2, we validate the olfactory pathway as a major entry point into the brain in vivo and demonstrate in vitro that SARS-CoV-2 travels retrogradely and anterogradely along axons in microfluidic neuron-epithelial networks.
Topics: Animals; Cricetinae; COVID-19; SARS-CoV-2; Genome, Viral; Axons; Olfactory Bulb; Virus Internalization; Viral Load; Genetic Variation
PubMed: 37495586
DOI: 10.1038/s41467-023-40228-7 -
Cureus Jul 2023The coronavirus disease 2019 (COVID-19) infection commonly presents with symptoms of fever, cough, and anosmia. However, there have been case reports of unusual symptoms...
The coronavirus disease 2019 (COVID-19) infection commonly presents with symptoms of fever, cough, and anosmia. However, there have been case reports of unusual symptoms associated with COVID-19. We encountered one such case where a 55-year-old male who tested positive for COVID-19 was noted to have, along with cough and vomiting, a new onset of left eyelid ptosis. COVID-19 infection and ptosis association is seldom seen and very few similar studies are reported.
PubMed: 37554604
DOI: 10.7759/cureus.41574 -
Biomedicines May 2024Olfactory dysfunction is a well-known phenomenon in neurological diseases with anosmia and hyposmia serving as clinical or preclinical indicators of Alzheimer's disease,... (Review)
Review
BACKGROUND
Olfactory dysfunction is a well-known phenomenon in neurological diseases with anosmia and hyposmia serving as clinical or preclinical indicators of Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. Since glaucoma is a neurodegenerative disease of the visual system, it may also entail alterations in olfactory function, warranting investigation into potential sensory interconnections.
METHODS
A review of the current literature of the last 15 years (from 1 April 2008 to 1 April 2023) was conducted by two different authors searching for topics related to olfaction and glaucoma.
RESULTS
three papers met the selection criteria. According to these findings, patients with POAG appear to have worse olfaction than healthy subjects. Furthermore, certain predisposing conditions to glaucoma, such as pseudoexfoliation syndrome and primary vascular dysregulation, could possibly induce olfactory changes that can be measured with the Sniffin Stick test.
CONCLUSIONS
the scientific literature on this topic is very limited, and the pathogenesis of olfactory changes in glaucoma is not clear. However, if the results of these studies are confirmed by further research, olfactory testing may be a non-invasive tool to assist clinicians in the early diagnosis of glaucoma.
PubMed: 38790964
DOI: 10.3390/biomedicines12051002 -
British Medical Bulletin Sep 2023Long COVID is a chronic condition that follows after acute COVID-19 and is characterized by a wide range of persistent, cyclic symptoms. (Review)
Review
INTRODUCTION
Long COVID is a chronic condition that follows after acute COVID-19 and is characterized by a wide range of persistent, cyclic symptoms.
SOURCES OF DATA
PubMed search for publications featuring 'Long COVID' or 'post-acute sequelae of COVID-19'.
AREAS OF AGREEMENT
Long COVID occurs frequently post-acute COVID-19, with a majority of people experiencing at least one symptom (such as cough, fatigue, myalgia, anosmia and dyspnoea) 4 weeks after infection.
AREAS OF CONTROVERSY
The specific symptoms and the minimum duration of symptoms required to be defined as Long COVID.
GROWING POINTS
There is a consistent reduction in Long COVID incidence amongst vaccinated individuals, although the extent of this effect remains unclear.
AREAS TIMELY FOR DEVELOPING RESEARCH
There is an urgent need to understand the causes of Long COVID, especially extreme fatigue more than 6 months after infection. We must understand who is at risk and whether reinfections similarly risk Long COVID.
Topics: Humans; COVID-19; Disease Progression; Fatigue; Post-Acute COVID-19 Syndrome
PubMed: 37434326
DOI: 10.1093/bmb/ldad016