The fatigue and “brain fog” of long COVID have been frustratingly hard to pin down — real to those who suffer them, but often invisible on standard tests. New brain-imaging research offers a possible physical explanation: a loss of dopamine-releasing neurons in key brain regions.
What the scans revealed
Researchers at Toronto’s Centre for Addiction and Mental Health (CAMH) used PET (positron emission tomography) scans to measure the health of dopamine neurons — brain cells that release dopamine, a chemical messenger central to motivation, movement and memory. Compared with healthy controls, long-COVID patients showed substantially reduced levels of a dopamine marker across major regions of the striatum, a deep brain structure — a signature of damage to dopamine-releasing neurons. The findings were published in eBioMedicine.
Matching damage to symptoms
What makes the study compelling is that the pattern of damage lined up with specific symptoms. Damage in the ventral striatum was linked to loss of motivation; damage in the dorsal putamen to slower movement; and damage in the caudate region to memory problems. That correspondence strengthens the case that dopamine-neuron loss isn’t incidental but may actually be driving the hallmark complaints of long COVID. “Long COVID involves the loss of dopamine-releasing neurons,” said Dr. Jeffrey Meyer, who noted the mechanism “may contribute to memory difficulties in other neurological conditions” as well.
Why this could lead to treatment
Crucially, dopamine is a system that medicine already knows how to influence — dopamine-targeting drugs are used in Parkinson’s disease and ADHD. If long-COVID fog stems partly from a dopamine deficit, then modifying dopamine activity might ease it. The researchers say a clinical trial is planned to test whether adjusting dopamine function can improve memory, motivation and fatigue in long-COVID patients — turning a mechanistic insight into a potential therapy.
The inflammation link
The finding also fits the team’s earlier work, which documented elevated brain inflammation in the very regions that house dopamine neurons. That suggests a plausible chain of events: infection triggers inflammation, inflammation damages dopamine neurons, and the resulting deficit produces fog, fatigue and slowed thinking — a coherent biological story for a condition often dismissed as vague.
Why it matters — and the caveats
For the millions with long COVID, evidence of a measurable, physical brain change is validating and, more importantly, actionable — it points to a specific target. But caution is warranted: this is a relatively small imaging study showing an association, not definitive proof that dopamine loss causes the symptoms, and the planned treatment trial has yet to show a dopamine-based therapy actually helps. It’s a strong, testable lead — a beginning, not a cure. Not medical advice.