LONDON — For many COVID-19 patients, their brief battle with the virus has led to a long-term loss of smell. Now, a new study finds that a bout of long COVID can actually alter a patient’s brain activity, cutting off communication which processes smell information. Importantly, researchers at University College London say they now know where this damage is taking place in the brain.
The UCL team used MRI scans to compare the differences in brain activity between people with long COVID who lost their sense of smell, those who regained their sense of smell after a COVID-19 infection, and healthy individuals who never tested positive for the virus. Results show those with long COVID had reduced brain activity and less communication between two key regions: the orbitofrontal cortex and the pre-frontal cortex. These brain areas help to process different smells and relay that information through the brain. When you cut off that line of communication, a person can’t make sense of what they’re sniffing.
The scans also show that people who recovered from COVID-19 and regained their sense of smell after did not have impaired brain activity in these regions. Since anosmia, the clinical term for smell loss, is reversible, study authors say it’s possible to “retrain” a person’s brain to recover their lost senses after COVID.
“Persistent loss of smell is just one way long COVID is still impacting people’s quality of life – smell is something we take for granted, but it guides us in lots of ways and is closely tied to our overall wellbeing. Our study gives reassurance that, for the majority of people whose sense of smell comes back, there are no permanent changes to brain activity,” says study lead author Dr. Jed Wingrove (UCL Department of Medicine) in a media release.
Long COVID brains may also be rewiring themselves
The study also reveals that the brains of those with long COVID and no sense of smell appear to be compensating for the loss by boosting other connections and sensory regions. This includes patients showing increased brain activity in regions that process smell and those which process sight — in 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 explains.
“Our findings highlight the impact COVID-19 is having on brain function. They raise the intriguing possibility that olfactory training – that is, 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,” adds joint senior author Professor Claudia Wheeler-Kingshott from UCL Queen Square Institute of Neurology.
“This is the first study to our knowledge that looks at how brain activity changes in people with long COVID smell loss. It builds on the work we undertook during the first wave of the pandemic, which was one of the first to describe the link between COVID-19 infection with both loss of smell and taste,” concludes study senior author Professor Rachel Batterham from the UCL Division of Medicine.
The findings are published in the journal eClinicalMedicine.