Even mild COVID-19 can damage the brain, affecting a person's ability to perform complex tasks, study finds

brain scan COVID — A COVID-19 patient's MRI images at are examined in Houston, Texas on December 10, 2020.
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A study of 785 British adults suggests COVID-19 can damage the brain in subtle ways, even after mild infections.
Researchers estimate the changes, which can impair cognitive function, correspond to an extra 1 to 10 years of aging.
It's still unclear how much the damages can be reversed and healed over time.

A new, years-long study of hundreds of older adults in the UK suggests that getting COVID-19 can damage the brain — reducing the amount of grey matter, affecting the health of brain tissue, and potentially impairing a person's ability to perform complex tasks.

The brain changes seen after coronavirus infections were subtle, reflecting small differences between infected and uninfected participants.

But the brain differences were still statistically significant — even though more than 95% of the COVID-positive patients in the study had mild or asymptomatic infections which didn't require hospitalization — an indication that the presence of the virus was responsible for the changes.

"We are not talking about gross pathology here, that a neuroradiologist would be able to immediately identify looking at the scan, we're talking about subtle differences of 0.2 to 2%," lead study author Gwenaëlle Douaud, a neuroimaging expert at the University of Oxford, told Insider.

The only reason the researchers in this study were able to pick the differences out is because they scanned the brains of the 785 study participants twice — once before the pandemic began, and then again in early 2021, after about half of them had been infected with SARS-CoV2, the virus that causes COVID-19.

The differences in the brains of the people who'd been infected with the virus may be equivalent to about an extra one to 10 years of aging, she said. The most pronounced changes were seen in the brains of older patients in the study, whose ability to perform complex tasks was impaired further by the infection.

"It is, to some extent, quite a scary result because 96% of our participants had mild infection," Douaud said. The other 4% of study participants were ill enough to require hospitalization.

The study lends more gold-standard evidence to a trend that other researchers studying cognitive decline, as well as long COVID, and other viral complications among younger COVID-19 patients have found — that the severity of a COVID-19 infection isn't necessarily a good predictor of negative long-term consequences from this virus.

COVID-19 patient brains 'shrunk a bit more'

The participants in this study, aged 51 to 81 years old, were all scanned during the first year of the pandemic, before Delta and Omicron emerged, and likely before any of them were vaccinated.

At that time, many people who were infected with the virus lost their sense of taste and smell, and that was reflected in this study as the researchers saw the biggest changes in the corresponding olfactory areas of their brains.

"But we also saw some global changes in the overall size of the brain, which had shrunk a bit more," Douaud said.

People who'd had COVID-19 scored lower than their peers (matched by age, sex, and risk factors) on the neuropsychological Trail Making Test, a dot-connecting exercise that is often used to measure executive functioning and cognitive decline, assessing how accurately and quickly participants can scan and process numbers and letters, and effectively switch between tasks.

It's unclear whether the brain may be able to heal itself after COVID-19

man at drive-thru testing site performs binaxnow rapid test on himself, as attendant waits at his window — "We need to bear in mind, again, that the level of scrutiny that we are dedicating to this is unprecedented," Douaud said.
William Campbell/Getty Images

Priti Balchandani, a professor of radiology, neuroscience and psychiatry, and director of the advanced neuroimaging research program at Mount Sinai's Icahn School of Medicine, who was not involved in the study, said it is a valuable and impactful piece of research, because the study was well-controlled, and the scanning protocol was consistent across participants.

"In this way, they can truly get a better picture of what's happening post-infection and whether or not the changes in the brain were truly attributed to the infection," she said. "You never want anything to cause changes in your brain beyond natural aging, but the brain is also very, very resilient and I am hopeful that overall these effects are not going to have severe alterations of neurological functions and they can likely be reduced in effect over time as the brain heals from the infection."

Scientists remain divided on what's causing brain changes in people infected with COVID-19, even with mild infections. It may be that the symptoms of COVID-19, such as losing the sense of smell, cause the brain to react, by turning off or shrinking the olfactory-related brain regions ("You don't use it, you lose it," as Douaud put it.) Some researchers believe, instead, that the changes are a result of brain inflammation, or the virus invading the brain in some regard. Another alternative explanation could be some combination of these factors.

Douaud, like Balchandani, has hope that neuroplasticity — the ability of the brain to grow, rearrange, and heal itself over time — may play a role in reversing at least some of the damage done to the brain due to the viral infection.

"We need to bear in mind, again, that the level of scrutiny that we are dedicating to this is unprecedented, and it could well be that influenza would create some effects that could be, maybe, similar," said Douaud, who is continuing to scan new patients to monitor the differences.

Balchandani agrees that this may not be unprecedented.

"There are similar, subtle effects sometimes seen in depression and other psychiatric illnesses that are often not diagnosed or assessed with neuroimaging," she said. "Recovery is possible, but so much is still unknown."

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