Anosmia, or lack of smell, is a hallmark symptom of coronavirus infection, which is still experienced by many people who have long since overcome the disease. Now, a study led by scientists at University College London (UCL) has found that people with prolonged loss of smell due to persistent COVID have different patterns of activity in some areas of the brain.
This is an observational study in which magnetic resonance imaging was used to compare the brain activity of people with prolonged COVID who had lost their sense of smell, with that of those who had recovered their sense of smell after infection by SARS-CoV- 2 and that of those who had never tested positive for COVID-19. The findings have been published in eClinicalMedicine.
The researchers found that people with prolonged loss of smell from COVID had reduced brain activity, and that in their case communication between two areas of the brain that process important information about smell—the orbitofrontal cortex and the prefrontal cortex—was impaired. while this connection had not been affected in individuals who had recovered their sense of smell after COVID.
An alteration of the brain that prevents processing odors
The results of the study suggest that the anosmia caused by persistent COVID is related to an alteration of the brain that does not allow it to process odors properly. The good news is that it is a reversible disorder and that the brain of those affected can be trained to recover their sense of smell.
“Retraining the brain to process different odors could help the brain regain lost pathways and people with long-term COVID to regain their sense of smell”
Dr Jed Wingrove from the UCL Department of Medicine and lead author of the study said: “Persistent loss of smell is just one way that COVID continues to affect people’s quality of life – smell is something that we take for granted, but it guides us in many ways and is closely related to our general well-being. Our study ensures that, for the majority of people whose sense of smell returns, there are no permanent changes in brain activity.”
“Our findings highlight the impact that COVID-19 is having on brain function. They raise the intriguing possibility that olfactory training, that is, retraining the brain to process different odors, could help the brain to regain lost pathways and people with long-term COVID to regain their sense of smell,” says Professor Claudia Wheeler- Kingshott of the UCL Queen Square Institute of Neurology) and joint lead author.
According to the researchers, their findings also suggest that the brains of people with prolonged loss of smell from COVID could be compensating for the lack of this sense by boosting connections with other sensory regions, since their brains had greater activity between the areas that are responsible for smelling. to process smell and those that process sight (the visual cortex). “This tells us that the neurons that would normally process the smell are still there, but they just work in a different way,” Wingrove says.
“This is the first study that we know of that looks at how brain activity changes in people with prolonged loss of smell from COVID. It builds on work we did during the first wave of the pandemic, which was among the first to describe the link between COVID-19 infection with loss of smell and taste, concludes Professor Rachel Batterham from the Division of Medicine of the UCL and co-senior author of the work.
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