How mild COVID virus damages the brain and cognition investigated

By Melissa Coade

March 9, 2022

People who caught mild forms of COVID-19 experienced shrinking of the overall size of their brains. (romaset/Adobe)

Health practitioners now understand so-called ‘COVID-brain’ a little better, with a new UK study showing that after people caught mild forms of the disease, they experienced shrinking of the overall size of their brains, as well as damage to parts of the brain related to memory and smell. 

The study of changes to 785 brains (401 belonging to people who tested positive for infection with SARS-CoV-2) in the UK has been published in Springer Nature

Researchers from Oxford University, University College London, the Imperial College and the US National Institutes of Health, analysed brain scans of UK Biobank participants aged between 51 and 81 years for the study. 

Two scans were taken for each person, on average 38 months apart, showing ‘various long-term effects’ for those who were infected with COVID compared to those who had dodged the virus. 

Of the 401 participants diagnosed with COVID, 15 were hospitalised, and MRI brain scans for the remaining 384 people were chosen as age- and sex-matched controls.

For the scans of COVID-positive patients, scientists found thinner grey matter in their orbitofrontal cortex and parahippocampal gyrus (responsible for controlling sense of smell and memories) and tissue damage in their olfactory cortex (an area linked to smell). Test subjects in the over-60s showed more marked brain changes.

Dr Sarah Hellewell from Curtin University’s Perron Institute for Neurological and Translational Science said that comparing MRI scans of participants before and after they had tested positive for COVID-19 was a novel way to demonstrate in a definitive way what the effects of a disease were.

The findings of the study are remarkable. The authors show that people who had mild COVID-19 infection an average of five months prior had thinning of brain tissue in several key brain regions, including those related to behaviour and emotion, as well as those located close to the nose,” Hellewell said.

“They also had alterations in their white matter connections between different brain regions, and slight decreases in cognitive function.

Cognitive decline for COVID positive people was also discovered between the time of the two MRI scans, associated with the atrophy of a brain region known as the cerebellum, which is linked to cognition. 

Another control group of people who had pneumonia unrelated to COVID-19 was used to demonstrate what neurological effects were specific to the SARS-CoV-2 virus. 

Dr Hellewell, who is unaffiliated with the study, explained that while the findings of the effect of COVID-19 on the brain may be applicable to Australia, there was no cause for panic.

The brain changes observed were relatively small and on a group level, so not everyone had the same effects,” Hellewell said.

“More research is needed to know whether these changes remain, reverse or get worse over time, and whether there are treatments that could help.”

The researchers added that further investigation was needed to understand the future vulnerability of the brains of people who have caught COVID-19. 

Commenting on the landmark study, the University of Western Australia’s Professor Paul Parizel said the paper was an example of the ‘tremendous scientific potential’ of big data analytics applied to brain research. 

“Surely, this should serve as a wake-up call for Australia to acquire all imaging data in a standardised and reproducible way, on calibrated instruments, and collect these data in an Australian imaging biobank,” Professor Parizel said.

“This will enable advanced data analytics to open new avenues for diagnosis, treatment monitoring, and possibly even prevention of diseases.”


Isolation impacts the brain, researchers say

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