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Today, a research paper in the form of an "Accelerated Article Preview" in the leading academic journal Nature highlights the impact of the new coronavirus (SARS-CoV-2) on the nervous system. Researchers at the University of Oxford in the United Kingdom conducted brain scans of hundreds of patients and found that after infection with the new crown virus, degenerative changes will occur in brain areas related to smell and memory.
For more than two years since the COVID-19 pandemic, we have recognized that COVID-19 is not just a respiratory disease, but affects multiple tissues and organs in the human body. For example, it affects the central nervous system, resulting in loss of smell and taste, fatigue, cognitive decline, and some patients also have stroke and more serious symptoms of impaired consciousness. There are even some studies reporting that some young people develop symptoms of Parkinson's disease after contracting the new crown.
In addition, a number of recent epidemiological investigations have shown that the possible health effects of multisystem injuries are long-term. Even patients with mild illnesses at first are at higher risk of multiple mental disorders, such as depression and anxiety, within a year of infection.
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Regarding the damage of the central nervous system by the new crown virus, some previous studies have found strong evidence in the examination of critically ill patients. How much has the brains of COVID-19 infected people affected the more common and larger numbers of mild cases? The study focuses on this more interesting issue.
To this end, researchers at the University of Oxford in the United Kingdom conducted the first longitudinal brain imaging study of new crown infection, using data from the UK Biobank to survey 785 participants (aged 51 to 81 years old). The participants had two brain scans, an average interval of nearly 3 years, and had been tested for cognition, so they could compare the changes before and after. About half (401 people) tested positive for COVID-19 between brain imaging, of which 15 were hospitalized, the vast majority of which were mild, and the rest were age- and sex-matched controls.
▲Brain imaging data analysis before and after infection showed that brain regions such as parahibacampal gyrus, olfactory cortex, and left orbitofrontal cortex showed longitudinal differences compared with the control group, showing decreased cortical thickness and increased tissue damage (Source: Reference[1])
Through imaging comparisons, the researchers observed three significant changes after infection. In the orbitofrontal cortex and paraeccampal gyrus, which are associated with olfactory and event memories, gray matter thickness has decreased significantly after COVID-19 infection. Moreover, in the brain region directly connected to the primary olfactory cortex, the signal of tissue damage is more pronounced. In addition, study subjects who have been infected with COVID-19 show signs of an average decline in overall brain volume.
Considering that the average interval between the confirmation of COVID-19 infection and the second brain scan by these participants reached 141 days, these brain changes associated with COVID-19 infection were part of a long-term effect.
Image credit: 123RF
The researchers also found through cognitive tests that, on average, subjects who had been infected with the new coronavirus experienced greater cognitive decline between scans, and even though 15 hospitalized cases were removed, a significant association was observed. In addition to the impact of the limbic and olfactory cortical systems of the brain, cognitive decline is also associated with increased atrophy in the cerebellum and associated with cognitive function.
The researchers conducted a controlled analysis in people with pneumonia unrelated to COVID-19, further suggesting that these changes are specific to COVID-19 and not the general effects of contracting respiratory diseases.
From these results, the loss of sensory input through olfactory pathways, inflammation of the nervous system, or loss of smell may be pathways to degenerative changes in the brain caused by COVID-19. As for whether these effects will last for a long time, and whether the effects will be partially reversible, scientists say it needs to be further tracked.
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