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COVID-19 may shrink some brain regions: UK study

Certain regions of the human brain may shrink after a person is infected with COVID-19, according to the first study to use brain scans to show ‘before and after’ images of the brain after infection.

A new UK study published on Monday in the journal Nature found there was greater tissue damage and shrinkage in the brains of people with even mild COVID-19, with most of the changes associated with it. related to areas of the brain associated with smell.

It is not yet clear whether these effects are permanent or will improve over time, or what they may mean for overall brain health or function, with the researchers noting that some Brain loss occurs with age.

To try to measure the impact of COVID-19, the researchers looked at brain changes in 785 people between the ages of 51 and 81 who underwent two brain scans and accompanying cognitive tests.

The key piece of data was that 401 participants had COVID-19 after the first scan and before the second scan, providing an opportunity to see if the images showed larger changes to the brain in those participate or not.

Compared with those who were not infected with COVID-19, brain scans of participants who had contracted the virus showed a greater reduction in gray matter in the brain, especially in the prefrontal cortex, and the parahippocampal gyrus, which is involved to the sense of smell.

The prefrontal cortex is also involved in social and emotional behavioral and decision-making processes, while the left agate gyrus was described in the study as “a limb region of the brain that plays an important role , integration for the relative chronological order of events in episodic memory. ”

In participants who had been infected with COVID-19, brain changes ranged from 0.2% to 2% compared with those without prior COVID-19 infection.

The data comes from the UK’s Biobank, a research source that regularly collects health data from 500,000 participants on-going to work on even more research projects.

From January 2021 to February 2022, the project asks participants who had their pre-pandemic imaging scans again to take additional images to help track the long-term effects of the virus on organs. viscera.

It was this move that made it possible to find participants who were scanned before and during the pandemic.

Previous research has found that COVID-19 can affect the brain, with many researchers indicating that common symptoms such as loss of taste or smell suggest neurological effects. But many studies looking at brain damage in COVID-19 cases have focused on people with severe viral infections who require hospitalization.

In this study, only 15 out of 401 severe COVID-19 infections required hospitalization.

“Using UK Biobank resources, we are in a unique position to look at the changes that take place in the brain following mild – as opposed to moderate or more severe – infection with SARS-CoV- 2,” Gwenaelle Douaud, a professor at the University of Oxford and lead author of the study, said in a press release.

“Despite the mild infection for 96% of the participants, we saw greater gray matter loss and greater tissue damage in those infected, an average of 4.5 months after infection. They also showed a greater decline in their mental ability to perform complex tasks, and this mental decline was partly related to these brain abnormalities. All of these negative effects were more apparent in older age groups. An important question for future brain imaging studies is whether this brain tissue damage resolves more permanently.”

In this study, researchers matched 401 cases with 384 participants who received both scans but did not contract COVID-19, making them a control group with a similar demographic.

All participants who contracted COVID-19 in the study group did so between March 2020 and April 2021, a period in which many variants, but not Omicron, is active.

The first and second scans were separated by an average of about three years, and the second scans occurred as early as one month after infection with COVID-19 for some participants and as late as six months for others. the others.

The researchers did not find any significant differences in the results of the second scan based on the amount of time that had passed after the participants contracted COVID-19.

Much of the tissue damage and changes in gray matter thickness are related to brain regions involved at least in part with the olfactory system, but the impact could extend beyond those regions, the researchers say.

“While the SARS-CoV-2-positive participants shrank and became more localized in some regions, mainly the fringes, the increase in [cerebrospinal fluid] whole brain volume and volume reduction suggest that an additional pervasive loss of gray matter superimposes the more regional effects observed in areas involved in olfaction,” the study states.

The infected but mostly mild symptoms in the study cohort did not show any signs of memory impairment, but exhibited impaired executive function, which was revealed through six cognitive tasks that participants were asked to perform.

When participants took a routine test that connects numbers, sometimes used as a screening tool for dementia, known as the Trail Making Test, people were infected COVID-19 took “significantly” longer to complete the test, the study said.

“A significantly larger cognitive decline, which persisted even after excluding hospitalized patients, was seen in the SARS-CoV-2 positive group between the two time points, and this decline is related to greater atrophy of the masticator II, a cognitive lobe of the cerebellum,” the study states, referring to a cerebellar appendage, the part at the back of the brain that coordinates physical movement .

While these effects on the brain may sound scary, the study notes that the structural changes are “modest,” saying that while there was “additional loss in participants with central average of 0.7% across brain regions involved in olfactory perception”, this should be analyzed with the knowledge that brain loss also occurs spontaneously, with older adults living independent with a 0.3% decrease in hippocampal volume per year.

However, being able to measure whether the virus is associated with additional changes in the brain that may not have been seen is valuable for further research and potential therapeutic solutions. .

It may also shed light on some of the lingering symptoms that affect people with prolonged COVID, including persistent brain fog and fatigue, although more research is still needed.

Stephen Smith, a professor at the University of Oxford and lead author of the study, said in a press release that being able to see scans of the same person taken before they contracted COVID-19 allows they have a unique opportunity to evaluate with more certainty. virus impact.

“The fact that we were scanned before infection helps us distinguish the brain changes associated with the infection from differences that might pre-existing in their brains,” Smith said.

“The UK Biobank COVID-19 Repeat Imaging Study is the only study in the world that has been able to demonstrate ‘before and after’ changes in the brain associated with SARS-CoV-2 infection,” said Naomi Allen , professor and principal scientist at the UK’s Biobank, added in the release.

“Collecting a second set of multi-organ scans from some people who have been infected with SARS-CoV-2 and from others who have not created a unique resource that allows scientists to understand how how the virus affects internal organs.”

Although the researchers attempted to investigate possible causes of confounding, including assessing whether the flu occurring between the first and second scans was related to brain outcomes, they also admitted that because this was an observational study, they could not say with absolute certainty that the brain changes were entirely caused by COVID-19.

“Our statistics also show average influence; Not all infected participants showed longitudinal brain abnormalities,” the study said.

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