If you’re among the estimated one-in-five Canadians who developed long COVID symptoms after infection with COVID-19, you might be familiar with the memory problems, focusing difficulties and a whole slew of other cognitive impairments that have become emblematic of the condition — collectively known as “brain fog.”

But despite these cognitive symptoms being present in nearly 90 per cent of long COVID cases, the biological mechanism behind why brain fog happens — and how we can treat it — has remained largely elusive. Until now.

A new paper, published in peer-reviewed journal Brain Communications, found that people living with long COVID had more significantly higher levels of a certain brain receptor than their healthy peers. The more they had, the worse their symptoms tended to get, the study suggested.

Long COVID, often attributed to a psychosomatic mechanism, has biological causes, a study reveals. Months after the infection, the virus was still active, at low levels, in the brainstem of hamsters.

“We hope to bring relief to the patients who may have heard that they are not sick, that it is ‘in their heads.’ What we are showing in the laboratory is that long COVID has a biological cause!,” says Guilherme Dias de Melo, a veterinarian and researcher in infectious diseases and neuropathologies at the Institut Pasteur. Eighty days after the initial infection, the COVID-19 virus was found, still infectious, in the brainstems of hamsters affected by symptoms similar to those of long COVID, according to the work that he has directed and published in the journal Nature Communications.