Catching Covid can cause changes in the brain, according to a study.
Scientists found significant differences in MRI (magnetic resonance imaging) scans before and after infection.
Even after a mild infection, the overall brain size had shrunk slightly, with less gray matter in areas related to smell and memory.
Researchers don’t know if the changes are permanent, but the stressed brain could heal.
The study was published in the journal Nature.
Lead author Prof Gwenaelle Douaud, from the Wellcome Center for Integrative Neuroimaging at the University of Oxford, said: “We looked at what was essentially a mild infection to see if we could really see some differences in her brain and how much her brain had changed compared to those who were not infected was quite a surprise.”
The UK biobank project has been tracking the health of 500,000 people for around 15 years and has a database of scans recorded before the pandemic, providing a unique opportunity to study the long-term health effects of the virus.
The scientists scanned again:
- 401 participants an average of 4.5 months after their infection, 96% of whom had mild Covid
- 384 participants who did not have Covid
They found:
- Whole brain size in infected participants had shrunk by 0.2 to 2%
- There were gray matter losses in the olfactory areas associated with smell and regions associated with memory
- Those who had recently recovered from Covid found it a bit harder to accomplish complex mental tasks
But researchers don’t know if the changes are reversible or really important for health and well-being.
“We have to keep in mind that the brain is really plastic – by that we mean it can heal itself – so there’s a really good chance that the harmful effects of an infection will wear off over time,” said Prof Douaud.
The greatest loss of gray matter has been in the olfactory areas – but it’s unclear whether the virus attacks this region directly or cells simply die from underuse after people with Covid lose their sense of smell.
It is also unclear whether all variants of the virus cause this damage.
The scans were performed when the original virus and the alpha variant were widespread and loss of smell and taste was a primary symptom.
But the number of people infected with the newer Omicron variant reporting this symptom has fallen dramatically.
“Your Mind Will Be Trained”
Paula Totaro lost her sense of smell when she caught Covid in March 2020.
“Once it was gone it was like living in a bubble or a vacuum – I found it really isolating,” she told BBC News.
But after contacting the AbScent charity, which supports people who have lost their ability to smell and taste, she began smell training.
“What smell training does — especially if you do it twice a day regularly and religiously — is that it forces you to take the smell, allow it to go back up your nose, and then think about what you’re smelling, ” She said.
“And that connection between what’s in the outside world and what’s going into your brain and your mind is what’s being trained.”
Ms Totaro has now regained most of her sense of smell – although she still struggles to discern what different smells are.
“It’s a mix of joy that the feeling has returned but still a bit of fear that I’m not quite there yet,” she said.
The UK Biobank’s chief scientist, Prof Naomi Allen, said: “It raises all sorts of questions for other researchers to explore about the impact of coronavirus infection on cognitive function, on brain fog and on other areas of the brain – and um to really focus on research on how best to mitigate that.”
Prof David Werring, of the University College London Institute of Neurology, said other health-related behaviors may have contributed to the changes observed.
“The changes in cognitive function were also subtle and of unclear relevance to daily functioning,” he said.
“And these changes are not necessarily seen in every infected individual and may not be relevant to newer strains.”
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