Long COVID brain fog is real — and now, we know what’s causing it. A breakthrough brain scan reveals the science behind the symptoms. Scientists in Japan have identified a biological cause behind the cognitive “brain fog” experienced by many Long COVID patients—a breakthrough that could lead to reliable diagnosis and treatment. A team at Yokohama City University used a cutting-edge brain imaging method to detect abnormal increases in AMPA receptors (AMPARs), molecules essential for learning and memory, in people suffering from Long COVID. These elevated receptor levels, observed using [11C]K-2 PET imaging, were closely linked to the severity of cognitive symptoms and inflammation markers, offering the first clear molecular explanation for the condition. The findings, published in Brain Communications, show that AMPAR density not only tracks with brain fog severity but also enables near-perfect distinction between affected and healthy individuals—100% sensitivity and 91% specificity. This offers promise for both diagnostic tools and treatments, such as drugs that suppress AMPAR activity. With brain fog affecting over 80% of Long COVID sufferers globally, this research marks a significant step toward validating the condition and accelerating efforts to address it with targeted therapies. [“Systemic increase of AMPA receptors associated with cognitive impairment of long COVID” by Yu Fujimoto et al., 1 October 2025, Brain Communications]