Brain scans have shown that a COVID-19 infection, even a mild one, might be linked to a significant loss of grey matter in the brain. This could explain why the virus is linked to a bunch of neurological symptoms, from brain fog and loss of smell to an increased risk of strokes.
The study, which has not yet been peer-reviewed, was recently posted on the preprint server medRxiv.
Scientists from the University of Oxford and Imperial College London documented evidence of brain changes in hundreds of patients who underwent magnetic resonance imaging (MRI) brain scans both before and after COVID-19 infections. The researchers looked at participants who had received brain scans before the pandemic as part of the ongoing UK Biobank study and invited 782 people back for a follow-up brain scan. Out of those who received a second scan, 394 had tested positive for SARS-CoV-2 infection between their two scans, and 388 people hadn’t been infected with the virus.
“To our knowledge, this is the first longitudinal imaging study in COVID-19 where COVID patients were initially scanned before they contracted the disease,” the researchers write.
The before and after scans showed the people who had been infected with the virus had a notable loss of grey matter in the left parahippocampal gyrus, the left lateral orbitofrontal cortex, and the left insula. The affected brain areas play a role in memory and emotional reactions, as well as people's sense of smell and taste. These changes were not seen in those who had not had a COVID-19 infection.
The next part of the study saw the researchers compare the brains of COVID-19 patients who had been hospitalized (15 people) with those who had not (379 people). According to the study authors, the differences “were not significant,” suggesting that even a relatively mild case of COVID-19 could physically impact the brain
Why COVID-19 is linked to a loss of grey matter, however, remains unclear. The researchers say it’s not certain whether it's a direct result of the virus infecting brain tissue or through another means, such as inflammation. They also note that further research is needed to understand this link between COVID-19 and physical changes to the brain. Just as other researchers have hinted, the changes seen in the brain, especially the hippocampus, might in time contribute to Alzheimer’s disease or other forms of dementia.
Speaking to IFLScience in May 2021, Professor Tim Spector — a Professor of Genetic Epidemiology at Kings College London who leads the ZOE COVID Symptom Tracker -— remarked: "Are people who had COVID-19 but got better after a few weeks — people who have lost their sense of smell, which we know is a sign of nerve damage — is that going to somehow trigger early dementia? We know there are links to people losing their smell and dementia. We have no idea about that because we understand very little of how the virus causes this damage, but I think it’s an open question."