Even though the COVID-19 pandemic began several years ago, scientists are still working to understand all of its long-term effects.
One of the most troubling outcomes is Long COVID—a condition where people continue to experience symptoms weeks or months after recovering from the initial infection.
One of the most common and frustrating symptoms of Long COVID is called “brain fog,” a kind of mental cloudiness that affects memory, focus, and thinking.
This affects more than 80% of people with Long COVID and can make it very hard to work or do everyday tasks.
Despite how common brain fog is, experts still don’t fully understand what causes it.
Some brain scans have shown small changes in the brain’s structure, but until now, researchers have not been able to see the specific problems happening at the molecular level—the small particles that help brain cells communicate.
Without this information, it’s been hard to confirm diagnoses or develop treatments.
That’s why a new study from Japan is so exciting. A team of researchers led by Professor Takuya Takahashi from Yokohama City University has found new clues that may explain what’s going on in the brains of people with Long COVID. Their study was published on October 1, 2025, in the journal Brain Communications.
The team focused on something called AMPA receptors, or AMPARs. These are tiny structures in the brain that play a key role in learning and memory.
Past studies of mental illnesses like depression and schizophrenia have linked problems with AMPARs to brain dysfunction. The researchers wondered if AMPARs might also be involved in brain fog from Long COVID.
To investigate this, they used a new brain imaging method called [11C]K-2 AMPAR PET. This allowed them to see and measure AMPARs in the living human brain for the first time. They compared the brains of 30 people with Long COVID to those of 80 healthy people.
What they found was surprising. People with Long COVID had more AMPARs spread throughout their brains. The more severe their brain fog symptoms were, the more AMPARs they had.
This shows a clear connection between these molecules and the thinking problems seen in Long COVID. They also found that inflammation in the body might be linked to these changes, suggesting that the immune system could be involved too.
This discovery is a big step forward. For the first time, researchers can see a direct biological cause for brain fog in Long COVID.
This could lead to new treatments. For example, medicines that reduce AMPAR activity might help reduce brain fog symptoms. Their imaging method was so accurate it could tell who had Long COVID and who didn’t with nearly perfect precision.
Professor Takahashi says their goal is to use this technology to better understand Long COVID and find new ways to treat it. He hopes this study shows the world that Long COVID brain fog is real and needs serious attention.
In the future, their work may help doctors diagnose Long COVID more easily and offer better care to those who are struggling with it. For now, this research offers new hope to millions of people living with the long-term effects of COVID-19.
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The study is published in Brain Communications.
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