Loss of taste and/or smell, states of confusion or delirium, loss of bearings, migraines, 'mental fog...' We now know that the neurological manifestations of COVID-19 can be very varied. What is less understood are the medium and long-term consequences of an infection on the human brain, even a trivial or asymptomatic one.
A team of researchers from the University of Oxford and the Imperial College London have addressed this question in a new study published in pre-print (and therefore not yet peer-reviewed) in the medical journal MedRxiv. Their findings suggest that even a small infection with COVID-19 can permanently alter the structure of the brain.
The effects of COVID-19 on the brain
To go about their study, the researchers used data from UK Biobank, a large British medical database that has been active since 2006 and is dedicated to research. They analysed and documented brain changes in patients who underwent magnetic resonance imaging (MRI) before and after their COVID infection, comparing the results with those of a control group of individuals with no history of the virus.
Of the 782 participants in their study, 394 tested positive for COVID-19 between March 2020 and April 2021. The other 388 were not ill and underwent the same test as a comparison. And in comparing the results, the researchers say they found 'a loss of grey matter' in specific parts of the brain in the infected individuals between the two scans. No changes were reported in the test group.
A loss of grey matter?
In detail, this loss of grey matter specifically affects the left parahippocampal gyrus, the left lateral orbitofrontal cortex and the left insular cortex. These are areas that partly govern memory, emotional reactions and certain sensory functions such as taste and smell, according to the specialist website IFL Science.
In the rest of their study, the researchers state that the differences 'were not significant' between those who were hospitalised at the time of their infection (15 people) and those who were not (the 379 others). This suggests that the severity of an infection does not play a predominant role in the extent of changes made to the brain.
While the results of the study seem convincing, it is unclear why COVID-19 affects the brain. The researchers are not sure whether this is a direct result of the infection, believing that it could also be the result of inflammation or other factors. They say that further research is needed to understand the link between the virus and the brain changes seen in this study.