The brain scans revealed lower overall cerebral blood flow — the amount of blood reaching the brain — in the long COVID group. The differences were largest in several regions involved in attention, sensory processing and cognitive control, the mental skill that helps us plan, focus and juggle tasks. Lower blood flow also tracked with slower reaction times.

The finding fits with earlier neuroimaging research. Previous studies have reported differences in brain blood flow or oxygen metabolism in people with post-COVID conditions, although results vary across studies and researchers have not established exactly how these changes relate to symptoms.

The researchers are careful about what the results do and do not show. The study found associations, not cause and effect. Lower cerebral blood flow might contribute to fatigue, result from another underlying process, or accompany symptoms for an unrelated reason. The small sample size also means the findings need testing in much larger groups before firm conclusions can be drawn.

The MRI method has its own limits. It cannot fully distinguish between reduced blood flow within brain tissue itself and changes in how blood moves through the brain's small blood vessels.

Long COVID is complex in its own right. Research suggests it can involve several body systems and biological processes at once, and the balance likely differs from person to person. Changes in immune and nervous system function have also been implicated, and no single explanation has emerged. The blood-flow differences in this study cannot account for everyone's fatigue.

The scan also cannot currently diagnose long COVID fatigue in an individual patient. Routine clinical tests, the authors note, may still fail to capture biological changes tied to symptoms that significantly disrupt someone's daily life — one reason patients with real, measurable physiology behind their exhaustion can come away from medical appointments without answers.

What the study does provide is another piece of evidence that persistent fatigue after COVID can coincide with measurable physiological differences in the brain. Whether reduced cerebral blood flow directly contributes to symptoms, and whether it could eventually help guide treatment, remains an open question. Answering it will require larger studies that follow people over time, rather than comparing groups at a single moment.

For the millions managing the condition in the meantime, the work adds to a growing body of research taking post-COVID fatigue seriously as a biological phenomenon — not simply a subjective complaint.