Long Covid smell loss linked to changes in the brain

A recent study led by UCL researchers has 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 an 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 study compared the brain activity of individuals with long Covid and loss of smell, those who had recovered their sense of smell after Covid, and individuals who had not tested positive for Covid-19.

The study’s results indicate that long Covid-related anosmia is connected to a brain alteration that hinders proper processing of smells. 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.

The lead author of the study, Dr Jed Wingrove from UCL Department of Medicine, stated 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. Dr Wingrove emphasized that the study provides reassurance that, for most people who recover their sense of smell, there are no lasting changes to brain activity.

Professor Claudia Wheeler-Kingshott, joint senior author from UCL Queen Square Institute of Neurology, stated that “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.”

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,” said Dr Wingrove.

Professor Rachel Batterham, a joint senior author of the study and from the UCL Division of Medicine, said that their study is the first to look at how the brain activity changes in people who experience loss of smell due to long Covid. She also added that their research builds on their work during the first wave of the pandemic, which described the link between Covid-19 infection and the loss of both smell and taste.

The study was funded by the National Institute for Health and Care Research (NIHR).