While scientists have strong evidence that COVID-19 can cause abnormalities in the brain, a lack of understanding around whether or not mild coronavirus (SARS-CoV-2) infection can lead to brain-related changes has remained, as well as what underlies those changes. 

Now, the world’s first study of the brain using magnetic resonance imaging (MRI) before and after COVID-19 may help to explain the “brain fog” many experience even after a mild infection.

What The Researchers Did

In a study published in the journal Nature, a team of investigators from the U.K. set out to learn more about brain-related changes in COVID-19 using the U.K. Biobank, a large database of biomedical information on about a half-million U.K. citizens.

• A total of 785 adults, 51-81 years of age, who had two MRI images of the brain taken roughly 3 years apart were identified for analysis.
• Of these participants, 401 were diagnosed with SARS-CoV-2 prior to their second brain scan.
• Cognitive function tests were also performed at the time of the MRIs.
• The 384 remaining adults functioned as controls for comparison.

The researchers noted that all Biobank centers employ the same advanced MRI technology and protocols. They also noted that having access to pre-infection imaging data reduces the odds of misinterpreting any pre-existing issues as effects of COVID-19.

What They Found

Compared to controls, the researchers found greater brain changes in those infected with SARS-CoV-2. They had:

• Thinner grey matter and less tissue contrast in the brain’s orbitofrontal cortex and parahippocampal gyrus, areas involved in such functions as reward, emotions, decision-making, and memory
• More indication of tissue damage in the brain areas connected to the primary olfactory cortex, which is involved in the sense of smell
• Less overall brain size, and reduced cognitive function between brain scans

Though some grey matter loss is normal over time, those infected had tissue loss in their parahippocampal gyrus, orbitofrontal cortex, and insula ranging from 0.2%-2% between MRIs.

Most of the infections were mild, yet these brain differences persisted after excluding 15 cases of severe COVID-19 that required hospitalization.

What It Means

The authors and other experts are quick to warn against premature conclusions, saying the brain changes were “modest” and further study is needed. It remains to be learned whether these changes are from disease effects spreading in the brain or the actual virus, and whether the brain’s limbic system, including memory, are at particular risk from COVID.

Still, the findings may help explain why some people who’ve recovered from acute infection experience long-term brain symptoms. Max Taquet, Ph.D. of the National Institute for Health and Care Research, Oxford Health BRC, wonders about the causes of these brain changes, whether they can be prevented or reversed, and whether they’re observed in more serious cases, in children, and in other groups.

Alan Carson, M.D., a professor of neuropsychiatry at the University of Edinburgh’s Center for Clinical Brain Sciences, explained that such modest brain changes could simply be due to a “change in mental experience.” But at minimum, he said, “What this study almost certainly shows is the impact, in terms of neural changes, of being disconnected from one’s sense of smell.”

*Whitlock Burton, K. (2022, March 8). First ‘Before-and-After’ COVID Brain Imaging Study Shows Structural Changes. Medscape. https://www.medscape.com/viewarticle/969906