Rebecca Morelle – BBC News Science Editor
Catching covid-19 can cause changes in the brain, suggests a study published in the scientific journal Nature
Scientists found significant differences in MRI scans performed on patients before and after infection.
Even after a mild infection, overall brain size had shrunk somewhat, with less gray matter in parts related to smell and memory.
The researchers don’t yet know if the changes are permanent, but they point out that the brain is able to recover.
“We were looking at a mostly mild infection, to see that we could actually see some differences in (the patient’s) brain and how much their brains had changed compared to those who hadn’t been infected,” said Gwenaelle Douaud. , lead author. of the study, from the Wellcome Center for Integrative Neuroimaging, University of Oxford, UK.
The UK Biobank project has been monitoring the health of 500,000 people for around 15 years and has a database of exams recorded before the pandemic, providing a unique opportunity to study the long-term health impacts of the virus.
The scientists again carried out tests on:
– 401 participants, performed 4.5 months, on average, after infection (96% of whom had mild covid);
– 384 participants who did not have covid.
And found that:
– The overall brain size of infected participants decreased by 0.2-2%;
– There were losses of gray matter in the olfactory areas and regions related to memory;
– Those who had recently recovered from Covid found it a bit harder to perform complex mental tasks.
But researchers don’t know to what extent 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 which we mean it can heal itself – so there is a good chance that over time the harmful effects of infection will attenuate”, explains Douaud.
The greatest loss of gray matter has been in the olfactory areas – but it’s unclear if the virus attacks this area directly or if the cells simply die from lack of use after people with covid lose their smell.
It is also unclear whether all variants of the virus cause this damage.
The tests were done when the original virus and the alpha variant were predominant, and loss of smell and taste was one of the main symptoms.
But the number of people infected with the omicron variant reporting this type of symptom has dropped dramatically.
“Your mind is what is exercised”
Paula Totaro lost her sense of smell when she became covid, in March 2020.
“When he disappeared it was like living in a bubble or a vacuum – I felt isolated,” she told BBC News.
But after contacting the charity AbScent, which supports people who have lost their sense of smell and taste, she began to train her sense of smell.
“What smell training does – especially if you do it twice a day, regularly, religiously – is it forces you to smell it, allows it to come back into your nose, and then think about what you feel,” he explains.
“And that connection between what’s in the outside world and what’s going on in your brain and your mind is what’s being exercised.”
Totaro has now regained most of his sense of smell, although he still has trouble identifying the different smells.
“It’s a mix of joy that the meaning has returned, but still a bit of anxiety that it hasn’t arrived yet,” she says.
About the study, UK biobank chief scientist Naomi Allen says: “It opens up all sorts of questions that other researchers might follow about the effect of coronavirus infection on cognitive function, the fog cerebral and other areas of the brain — and really focus research on how best to mitigate that.”
Professor David Werring, from the Institute of Neurology at University College London (UCL), also in the UK, said other health-related behaviors may have contributed to the observed changes.
“Changes in cognitive function were also subtle and of unclear relevance to daily functions,” he notes.
“And these changes are not necessarily seen in all infected individuals and may not be relevant to new strains.”
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