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The first major study to compare brain scans taken before and after people tested positive for coronavirus has indicated the virus can cause the brain to shrink.
Conducted by researchers from the University of Oxford, the study involved 785 people aged between 51 and 81 who received brain scans both before and during the pandemic as part of the UK Biobank study.
Of the participants, 401 tested positive for coronavirus between the two scans, allowing Professor Gwenaëlle Douaud and colleagues to study the effects the virus can have on the brain.
COVID-19 can cause the brain to shrink and damage areas linked to memory and smell, says a new study by Oxford University that was published in the Nature journal https://t.co/NUfZDlXksM pic.twitter.com/B7hk1VAc4X— Reuters (@Reuters) March 8, 2022
Researchers used the scans of those who had tested positive for coronavirus and compared them with 384 control subjects who had not been infected, and who were similar to the other group in age, sex, and a number of risk factors including blood pressure, obesity, smoking, socio-economic status and diabetes.
Following the comparison, the scientists found there was greater overall brain shrinkage and more grey matter shrinkage, particularly in areas linked to smell, in those who had tested positive.
More specifically, those who had coronavirus lost, for example, an additional 1.8% of the parahippocampal gyrus, an area of the brain key for smell, and an additional 0.8% of the cerebellum when compared with control subjects. A loss of smell is a known symptom of coronavirus, and this may be due to disrupted signal processing in these areas of the brain.
As well as brain shrinkage, researchers found those who were infected also typically scored lower on a mental skills test. These lower scores have been associated with a loss of brain tissue in the parts of the cerebellum involved in mental ability.
In the research, which has been published in the journal Nature, the scientists note the effects on the brain were more pronounced in older people and those hospitalised by the disease than with other cases. However, the effects were still evident in patients with mild or asymptomatic infections.
The effects were identified, on average, 4.5 months following infection, though further scans will be necessary to determine whether the changes caused by coronavirus are permanent, or whether they are partially reversible.
The University of Oxford has explained the insight into the effects of coronavirus will 'contribute to our overall understanding of how the disease spreads through the central nervous system.'
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