Researchers find that long COVID sufferers with loss of smell show lower brain activity

A team of researchers from University College London (UCL) discovered that individuals with long COVID and anosmia exhibit distinct activity patterns in specific brain regions. Using MRI scanning, the study compared brain activity in individuals with long COVID experiencing anosmia, those who had recovered their sense of smell after COVID infection, and those who had never been infected with COVID-19.

According to their observational study published in eClinicalMedicine, individuals suffering from long COVID who experience loss of smell have lower brain activity and impaired communication between two regions of the brain responsible for processing smell information, namely the orbitofrontal cortex and the pre-frontal cortex.

The researchers state that the study’s results indicate that long COVID-related anosmia is connected to a brain alteration that hinders proper processing of smells. Experts say that the fact that this alteration can be clinically reversed in some individuals suggests that it may be feasible to retrain the brain and restore the sense of smell in those affected by long COVID.

UCL Department of Medicine’s Jed Wingrove, PhD, who lead the study, says that long COVID is still affecting people’s quality of life in many ways, including persistent loss of smell. “Smell is something we often overlook, but it plays a crucial role in guiding us and is closely connected to our overall well-being.” Wingrove emphasizes that the study provides reassurance that, for most people who recover their sense of smell, there are no lasting changes to brain activity.

“Our study sheds light on the impact of COVID-19 on brain function and suggests that olfactory training, which retrains the brain to process different scents, could potentially help people recover their sense of smell who are suffering from the long-term effects of COVID-19,” says Claudia Wheeler-Kingshott, PhD, joint senior author from UCL Queen Square Institute of Neurology.

According to the researchers, the study also implies that the brains of individuals with long Covid smell loss may be compensating for the loss by increasing connections with other sensory regions. The study observed increased activity between the regions of the brain responsible for processing smell and those responsible for processing vision (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,” says Wingrove.