Key points:
- People who have lost their smell due to long COVID show different patterns of brain activity.
- MRIs showed impaired communication between two parts of the brain that process important smell information.
- The researchers say it is possible to retrain the brain to recover its sense of smell.
Three-plus years after it made its way around the globe, scientists as still uncovering all the effects of COVID-19. Nowadays, with the virus at an endemic level, more and more research is focused on long COVID.
In a new study by researchers at the University College London (UCL), researchers have shown those living with a loss of smell from long COVID have different patterns of activity in certain regions of the brain.
For the study, published in eClinicalMedicine, the team used MRI scanning to compare the brain activity of three groups of people: those with long COVID who lost their sense of smell, those whose smell returned to normal after COVID-19 infection, and those who never tested positive for COVID-19.
The observational study found that the people with long COVID-linked smell loss had reduced brain activity and impaired communication between two parts of the brain that process important smell information—the orbitofrontal cortex and the pre-frontal cortex. This connection was not impaired in people who regained their sense of smell after COVID-19.
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 subjects—it may be possible to retrain the brain to recover its sense of smell in people suffering the side effects of long COVID.
“Our findings highlight the impact COVID-19 is having on brain function,” said senior author, Claudia Wheeler-Kingshott, professor at UCL. “They also raise the intriguing possibility that olfactory training—or retraining the brain to process different scents—could help the brain to recover lost pathways, and help people with long COVID recover their sense of smell.”
The team also noted that those with long COVID-linked smell loss had increased brain activity between the parts of the brain that process smell and areas that process sight. They believe this is because the brain is compensating for a lost sense by boosting connections with other sensory regions.
“This tells us that the neurons that would normally process smell are still there, but they’re just working in a different way,” said lead author Jed Wingrove from the UCL Department of Medicine.