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Covid-19 can cause greater loss of gray matter and tissue damage to the brain than would naturally occur in uninfected people. new work finds.

The study, published Monday in the journal Nature, is believed to be the first to include people who had a brain scan both before they contracted Covid and months afterward. Neuroscientists who were not involved in the study said it was valuable and unique, but cautioned that the effects of the changes are unclear and do not mean that people can have permanent damage or that the changes can profoundly affect thinking, memory or others. functions.

The study, which included people aged 51 to 81 years, found shrinkage and tissue damage primarily in brain regions related to the sense of smell; Some of these areas are also involved in other brain functions, the researchers said.

D., chief of neurological infections and global neurology at Yale School of Medicine. “To me, this is pretty convincing evidence that something has changed in the brains of this general group of people with Covid,” said Serena Spudich. study.

But he cautioned: “To conclude that this has some long-term clinical implications for patients, I think is a stretch. We don’t want to scare the public and make them think, ‘Oh, this is proof that everybody has brain damage and can’t work.'”

The study involved 785 participants in the UK Biobank, a repository of medical and other data from nearly half a million people in the UK. Each of the participants underwent two brain scans roughly three years apart, as well as some basic cognitive tests. Between the two scans, 401 participants tested positive for coronavirus, and all were infected between March 2020 and April 2021.

The other 384 participants formed the control group, as they were not infected with the coronavirus and had similar characteristics to infected patients in areas such as age, gender, medical history, and socioeconomic status.

With normal aging, people lose a very small piece of gray matter each year. The typical annual loss in memory-related regions, for example, is between 0.2 percent and 0.3 percent, the researchers said.

But the Covid patients in the study, who underwent a second brain scan an average of four and a half months after infection, lost more than uninfected participants, with an additional 0.2 percent to 2 percent loss of gray matter in different brain regions over three years. between scans. They also lost more overall brain volume and showed more tissue damage in specific areas.

Investigating the neurological effects of Covid, Dr. “I find it surprising in the sense of how much has been lost and how widespread it is,” Spudich said. “I didn’t expect to see so many percentage changes,” he added.

The effects may be particularly noteworthy because the study mostly included people – like the majority of Covid patients in the general population – who were mildly affected by their initial Covid infection and were not sick enough to be hospitalized.

The study’s lead author, Gwenaëlle Douaud, a professor in Oxford University’s department of clinical neuroscience, said that although the number of hospitalized patients in the study, 15, was too small to have definitive data, the results suggest brain atrophy. worse than mildly affected patients.

People who contracted COVID showed greater declines in a cognitive test of attention and efficiency in performing a complex task than people who were not infected. But outside experts and Dr. Cognitive testing is primitive, Douaud noted, so the study is very limited in what it can say about whether the gray matter loss and tissue damage experienced by Covid patients is affecting their cognitive abilities.

Associate professor of neurological infections at the University of Liverpool, Dr. “None of them did cognitive testing that was comprehensive enough to know if there were significant deficits in these many regions where they found these changes in volume,” said Benedict Michael. The neuropsychiatric effects of Covid and were not included in the study. “We don’t know if it really means anything to the patient’s quality of life or function.”

For example, although some of the greatest gray matter loss is in olfactory-related areas, including the orbitofrontal cortex and parahippocampal gyrus, these areas are also involved in memory and other functions. However, Dr. Douaud said that although the memory tests they conducted were short and simple, Covid patients did not perform worse on memory tests than uninfected participants.

The main cognitive assessment that Covid patients lack, tracking test, a dots exercise with alternating letters and numbers. Covid patients took longer to complete the task, suggesting weaknesses in focus, processing speed, and other skills.

Dr. This decreased ability is associated with loss of gray matter in a specific area of ​​the brain’s cerebellum, Douaud said. However, saying that the study did not prove cause and effect, Dr. Primarily associated with balance, coordination and movement, the cerebellum “is not the first brain structure you think of” to explain ability changes in the cerebellum, Spudich said. trail test.

Dr. A major limitation of the study was that the researchers did not know about people’s symptoms, including whether they lost their sense of smell, Douaud said. Researchers have also been unable to determine if any of the patients are long-term patients with Covid, so it’s unclear whether the findings are relevant to this long-term condition.

The differences between infected and uninfected people increased with age. For example, on the trailing test, performance for people in their 50s and 60s was similar in both groups, but the difference widened significantly after that. Dr. “I don’t know if it’s because young people are recovering faster or if they’re not as affected as they were at the beginning,” Douaud said. “It could be both, or it could be both.”

Dr. Michael warned that the findings may be unpredictable for many young people experiencing post-Covid brain fog and other cognitive problems. Because gray matter and tissue damage are only measured at one time point after infection, “we don’t know if there is a temporary change that gets better with healing,” he said.

Outside experts and the study’s authors said that the brain regions where Covid patients experience greater loss of gray matter raise intriguing questions.

Dr. “There isn’t one part of the brain that does one job,” Douaud said. “Infected participants have parts of the brain with additional loss of gray matter unrelated to smell, and those related to smell are also involved in other brain functions.”

The cause of the brain changes is unclear. The authors cited theories including: Inflammation with evidence from other studiesand “sensory deprivation” of impaired sense of smell.

D., head of the nervous system infections division at the National Institute of Neurological Disorders and Stroke, who was not involved in the study. Avindra Nath said another “critical question” is whether brain changes could make Covid patients more susceptible. dementia or other future deficits.

While researchers did not find the same brain changes in non-Covid-19 pneumonia patients, Dr. Nath recommended examining patients with other coronaviruses or flu “to see if these findings are different or more generalizable to Covid-19.”

Spudich said the study’s greatest value may be its indication that “something is going on in these people’s brains,” adding that “I think people felt it was very vague, very difficult to measure.”

He and others said other scientists can now build on these findings.

“This is an important study, they’ve done a good job,” Michael said, adding that “now we need to do studies to look at cognition and psychiatric symptoms, behavioral issues and neurological things and find out what it means for patients.”