Dr Max Taquet, of the University of Oxford, said: “It is well-established that Covid-19 infection is associated with subsequent risks of neurological and psychiatric problems in some people, including brain fog, loss of taste and smell, depression and psychosis.
“But why this occurs remains largely unknown. This study starts to shed light on this important question by showing that brain regions connected to the ‘smell centre’ of the brain can shrink after Covid-19 in some people.
“These findings might help to explain why some people experience brain symptoms long after the acute infection. The causes of these brain changes, whether they can be prevented or even reverted, as well as whether similar changes are observed in hospitalised patients, in children and younger adults, and in minority ethnic groups, remain to be determined.”
Those tested were aged between 51 and 84, with an average of 141 days between testing positive and being scanned. The researchers said the brain changes were not observed in every patient and that their results had been averaged out.
Dr Rebecca Dewey, research fellow in neuroimaging at the University of Nottingham, said: “If the findings were based on imaging data alone, I would say that we have much less reason to worry about this as the brain is so plastic that it is likely to compensate in the absence of any conditions preventing this.
“However, I find the significant association between the imaging findings and the cognitive tests highly compelling. The authors took great effort to show that this effect was not present prior to Covid.
“These sorts of changes are seen after many forms of disease onslaught, and even that of healthy ageing. The key difference shown here is that they appear to be happening faster than with ageing alone.”
Impact of disconnection from sense of smell
Many people lose their smell during a Covid infection, and the brain loss may be due to a loss of sensory impact in the brain, in the same way as hearing loss is a risk factor in cognitive decline.
Alan Carson, professor of neuropsychiatry at the University of Edinburgh, said: “What this study almost certainly shows is the impact, in terms of neural changes, of being disconnected from one’s sense of smell.
“It serves to highlight that the brain connects to the body in a bidirectional relationship that is both structurally and functionally dynamic.”
It comes as scientists, led by the University of Edinburgh, have identified 16 genes that increase a person’s risk of becoming severely ill with Covid.
They are involved with bodily functions including blood clotting, inflammation and controlling the immune system. Academics hope that by identifying these genetic regions they can find drugs to help treat people at greatest risk of life-threatening complications.