Biological Evidence of COVID-Related 'Brain Fog' Discovered by Scientists

Work on treating long COVID is still in its early stages.

Published: 10/8/2025, 4:19:41 PM EDT

Biological Evidence of COVID-Related 'Brain Fog' Discovered by Scientists — Brain fog can be frustrating, but the good news is there are a variety of treatment options. (Screenshot via NTD)

The biological cause of long COVID-related "brain fog" has been discovered by Japanese scientists, with their findings revealing interesting information about this confounding ailment, which cause is still not entirely understood.

The Japanese research team, led by Takuya Takahashi, a professor in the Department of Physiology at the Graduate School of Medicine at Yokohama City University, published the findings in Brain Communications magazine this month.

As explained in the publication, long COVID manifests as various symptoms, including cognitive or memory impairments, which are colloquially known as "brain fog." This side effect of "sluggish thinking" is said to impact over 80 percent of those with long COVID. And as the World Health Organization has acknowledged, six in every 100 people who have had COVID-19 later suffer from long COVID.

And while nearly six years have passed since the beginning of the COVID-19 pandemic, the cause of these COVID-19-related ailments is not fully understood.

The impact of long COVID's "brain fog" symptom is troubling for those afflicted with it, not just because of impairments to reasoning, memory and executive functions, but millions of sufferers may also have to scale back normal, daily activities, or even quit their job and find new employment, if they are even able to, in the wake of this crippling cognitive condition.

As Takahashi and his team noted: "Therefore, [long COVID] is considered a major burden not only to individuals’ daily activities but also in the global socioeconomic context, estimated at approximately $1 trillion resulting from over 400 million global cases of Long COVID."

Hypothesizing that patients might exhibit "disrupted expression of AMPA receptors (AMPARs)-key molecules for memory and learning-based on prior research into psychiatric and neurological disorders such as depression, bipolar disorder, schizophrenia, and dementia."

Thirty test subjects with long COVID were utilized for the Yokohama University study. Those 30 were then compared to the results of 80 healthy volunteers.

As noted in the study, not only was receptor density significantly higher in patients, along with higher AMPAR activity, but the worse the cognitive symptoms were. Additionally, inflammation was present, and higher levels of inflammatory markers were linked to the same receptor increases, suggesting that the brain’s immune response may be driving the molecular changes.

“By applying our newly developed AMPA receptor PET imaging technology, we aim to provide a novel perspective and innovative solutions to the pressing medical challenge that is Long COVID,” Takahashi said.

“Our findings clearly demonstrate that Long COVID brain fog should be recognized as a legitimate clinical condition. This could encourage the healthcare industry to accelerate the development of diagnostic and therapeutic approaches for this disorder,” explains Takahashi.

Work on treating long COVID is still in its early stages. However, the new findings could help going forward. Treatments reducing excessive AMPAR activity could potentially help those affected with the new disease.

NTD reached out to Takahashi via email, seeking additional comment on the reported findings. As of press time, NTD had not received a reply.