People living with long Covid who suffer from loss of smell show different patterns of activity in certain regions of the brain, a new study has found.
The research from University College London used MRI scanning to compare the brain activity of people with long Covid who lost their sense of smell, those whose smell had returned to normal after Covid infection, and people who had never tested positive for Covid-19.
Published in eClinicalMedicine, the observational study found that the people with long Covid smell loss had reduced brain activity and impaired communication between two parts of the brain which process important smell information: the orbitofrontal cortex and the prefrontal cortex.
This connection was not impaired in people who had regained their sense of smell after Covid.
The findings suggest smell loss, known as anosmia, caused by long Covid is linked to a change in the brain that stops smells from being processed properly.
Because it's clinically reversible, as shown in some people, it may be possible to retrain the brain to recover its sense of smell in people suffering the side effects of long Covid.
"Persistent loss of smell is just one way long Covid is still impacting people's quality of life. Our study gives reassurance that, for the majority of people whose sense of smell comes back, there are no permanent changes to brain activity," said lead author Dr Jed Wingrove from UCL Department of Medicine.
Researchers say their findings also suggest that the brains of people with long Covid smell loss might be compensating for this lost sense by boosting connections with other sensory regions: their brains had increased activity between the parts of the brain that process smell and areas that process sight (the visual cortex).
"This tells us that the neurons that would normally process smell are still there, but they're just working in a different way," Dr Wingrove said.