Even mild cases of COVID-19 leave a mark on the brain – but it’s not clear how long it lasts yet

New research shows that COVID-19 could affect the body and brain for months or more after infection.

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With more than 18 months of the pandemic in the rearview mirror, researchers have steadily gathered new and important information about the effects of COVID-19 on the body and brain. These findings raise concerns about the long-term impacts the coronavirus could have on biological processes such as aging.

As a cognitive neuroscientist, my previous research has focused on understanding how normal brain changes associated with aging affect people’s ability to think and move, particularly in middle age and beyond. But as more and more evidence showed that COVID-19 could affect the body and brain for months or more after infection, my research team became interested in exploring how it could also impact the body. natural process of aging.

Observe the brain’s response to COVID-19

In August 2021, a preliminary but large-scale study examining brain changes in people with COVID-19 garnered a lot of attention within the neuroscience community.

In this study, the researchers drew on an existing database called UK Biobank, which contains brain imaging data from more than 45,000 people in the UK since 2014. This means – crucially – that it there was background data and brain imaging of all of these people. before the pandemic.

The research team analyzed the brain imaging data, then brought back those who had been diagnosed with COVID-19 for further brain scans. They compared people who had suffered COVID-19 to participants who had not, carefully matching groups based on age, gender, date of baseline test, and location of the test. study, as well as common risk factors for disease, such as health variables and socioeconomic status.

The team found marked differences in gray matter – which is made up of the cell bodies of neurons that process information in the brain – between those who had been infected with COVID-19 and those who had not. Specifically, the thickness of gray matter tissue in regions of the brain known as the frontal and temporal lobes was reduced in the COVID-19 group, differing from the typical patterns seen in the group that had not experienced COVID. -19.

In the general population, it is normal to see changes in the volume or thickness of gray matter over time as people get older, but the changes were larger than normal in those who had been infected with COVID-19.

Interestingly, when researchers separated people who had an illness severe enough to require hospitalization, the results were the same as those who had suffered milder COVID-19. That is, people who had been infected with COVID-19 showed loss of brain volume even when the disease was not severe enough to require hospitalization.

Finally, the researchers also studied changes in performance on cognitive tasks and found that those who contracted COVID-19 were slower to process information, compared to those who did not.

Although we should be cautious in interpreting these results pending formal peer review, large sample size, pre- and post-disease data in the same people, and careful matching with people who had not had COVID-19 made this preliminary work particularly valuable. .

What do these changes in brain volume mean?

At the start of the pandemic, one of the most common reports of people infected with COVID-19 was loss of the sense of taste and smell.

Close up image of a woman smelling a peeled orange

Some patients with COVID-19 have experienced a loss or reduction in their sense of smell.

Dima Berlin via Getty Images

Surprisingly, the regions of the brain that British researchers have found affected by COVID-19 are all linked to the olfactory bulb, a structure near the front of the brain that transmits signals about smells from the nose to other regions of the brain. . The olfactory bulb is connected to the regions of the temporal lobe. The temporal lobe is often referred to in the context of aging and Alzheimer’s disease because that is where the hippocampus is located. The hippocampus is likely to play a key role in aging, given its involvement in memory and cognitive processes.

The sense of smell is also important for Alzheimer’s disease research, as some data suggests that those at risk for the disease have a reduced sense of smell. While it is far too early to draw conclusions about the long-term impacts of these COVID-19-related changes, studying the possible links between COVID-19-related brain changes and memory is of great importance. interest – especially given the regions involved and their importance in memory and Alzheimer’s disease.

Look ahead

These new findings raise important but unanswered questions: What do these brain changes following COVID-19 mean for the process and pace of aging? And, over time, does the brain recover to some extent from a viral infection?

These are active and open areas of research, some of which we are starting to do in my own lab in conjunction with our ongoing work on brain aging.

Brain images of a 35-year-old man and an 85-year-old man.

Brain images of a 35-year-old man and an 85-year-old man. Orange arrows show the finer gray matter in the older individual. Green arrows indicate areas where there is more space filled with cerebrospinal fluid (CSF) due to reduced brain volume. Purple circles highlight the ventricles of the brain, which are filled with CSF. In older people, these fluid-filled areas are much larger.

Jessica Bernard, CC BY-ND

Our lab’s work shows that as people age, the brain thinks and processes information differently. Additionally, we have observed changes over time in the way people’s bodies move and how people learn new motor skills. Decades of work have shown that older people have more difficulty processing and manipulating information – such as updating a mental grocery list – but they generally maintain their knowledge of facts and vocabulary. When it comes to motor skills, we know that older people still learn, but they do it more slowly than younger adults.

When it comes to the structure of the brain, we usually see a decrease in brain size in adults over 65. This decrease is not only localized in one area. Differences can be seen in many areas of the brain. There is also usually an increase in the cerebrospinal fluid that fills the space due to the loss of brain tissue. In addition, the white matter, the insulation of axons – long cables that carry electrical impulses between nerve cells – is also less intact in older people.

As life expectancy has increased over the past decades, more and more people are reaching old age. While the goal is for all to live long and healthy lives, even in the best of times when we age without disease or disability, adulthood brings about changes in the way we think and move.

Learning how all of these puzzle pieces fit together will help us unravel the mysteries of aging so that we can help improve the quality of life and functioning of aging people. And now, in the context of COVID-19, it will help us understand how well the brain can recover after illness as well.

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