As larger numbers of people recover from COVID-19, researchers are learning more about "brain fog" in those affected by the virus.

For months, doctors and researchers have been aware of a range of longer-term symptoms afflicting people after recovering from an active COVID-19 infection. One such symptom, generally referred to as "brain fog," can take the shape of confusion, difficulty thinking and concentrating, short-term memory loss, and in severe cases, has even been reported to cause delirium and psychosis.

While scientists still don't know for sure what causes brain fog, they're zeroing in on a few theories. Mainly, scientists increasingly believe brain fog happens when cells that are involved in response to an infection make their way to atypical places, such as the brain.

A key finding emerged when researchers autopsied brains of COVID victims, discovering certain cells that shouldn't have been there. These large cells, known as megakaryocytes, might be taking up precious space, leaving less room for blood to pass to the brain.

This phenomenon might be unique to COVID, according to David Nauen, MD, PH.D, a professor of pathology at the Johns Hopkins University School of Medicine.

"To have megakaryocytes in the brain has never been seen before, I couldn't find any reference in my search this past summer with megakaryocytes noted in human brain capillaries. This is very new for COVID that they are doing this," Nauen told ABC News. "This could help us bring up a better picture of what's going on."

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