Long COVID’s brain fog finally has a biological explanation: Dopamine loss

For years, long COVID has been defined almost entirely by what patients report feeling: fatigue, brain fog, memory lapses, a loss of motivation that won’t lift.

Doctors have struggled to treat a symptom with no clear physical marker, and the condition has reshaped workplaces as employers scramble to accommodate it.

But despite the shared symptoms, there’s been little for doctors to point to and say, “this is what changed in your body.” Now, a new study from researchers at the Centre for Addiction and Mental Health and the University of Toronto may start to change that.

Led by Jeffrey Meyer, a psychiatry professor at the University of Toronto, researchers used PET imaging to measure a protein called VMAT2, found on the nerve terminals that release dopamine, in 24 long COVID patients and 24 healthy people who’d had only mild or moderate initial infections.

The study found patients with long COVID had significantly lower VMAT2 levels across the brain region tied to motivation, movement, and memory (the striatum).

The reduction ranged from 16% in the region tied to planning (dorsal putamen) to 20% in the region most closely tied to motivation and apathy (ventral striatum).

“By showing that there’s reductions in the nerves that release dopamine in these areas, and then showing the relationship of them to the symptoms, that’s two pieces of information that makes a strong connection to long COVID,” Meyer told Fortune .

This builds on a 2023 study from his team, which found elevated inflammation in these same brain regions.

That study measured a different protein, one found on inflammatory cells.

“They’re measuring fundamentally different processes, but it may be that one is leading to the other,” he explained.

Inflammatory cells can damage the ends of dopamine-releasing nerves, or injury to the nerves themselves could be generating the inflammation.

What sets the new study apart, Meyer said, is how closely the imaging results tracked with specific symptoms.

Reduced dopamine markers in the region associated with apathy (ventral striatum) lined up with memory problems.

Markers in the planning region (dorsal putamen) tracked with slowed movement.