Feb 2024 | Trinity College | St. James’s Hospital | Nature

Study explores causes of “brain fog”

Researchers at Trinity College and St. James's Hospital in Ireland are currently investigating the causes of the so-called “brain fog”, which is affecting many people suffering from Long COVID. The symptom refers to impaired mental performance. This manifests itself, among other things, in a reduced ability to concentrate and memory difficulties.

The research team had already taken blood samples from 76 COVID-19 patients in the spring of 2020. Compared to a control group without COVID-19 disease, they observed increased levels of a protein (“S100 beta”), which is an indicator of an impaired blood-brain-barrier. The blood-brain-barrier is the transition between the bloodstream and the central nervous system and normally protects the brain from harmful substances. 

The researchers also examined 10 healthy persons, 11 persons with Long COVID without brain fog and 11 persons with Long COVID who suffer from the symptom of brain fog.

Using MRI images and a special contrast media, the research team was able to show that more contrast media passes through the blood-brain-barrier in people with Long COVID. The blood vessels have become more permeable due to the viral infection. The blood-brain-barrier can be disrupted both during an acute COVID-19 illness and in people suffering from Long COVID. Among other things, this allows cells and neurotransmitters of the immune system to reach the brain more easily. The researchers assume that more permeable blood vessels and an overactive immune system are primarily responsible for the “brain fog”. 

In future, the permeability of the blood-brain-barrier could be an important indicator of the neurological consequences of COVID-19 disease. More precise connections and possible treatment methods derived from this are still being researched.

Article in the journal Nature

Trinity College

Trinity College is a renowned university in Dublin, Ireland. Established in 1592, it is one of the oldest universities in the world. 

St. James’s Hospital

St. James's Hospital is a hospital in Dublin, Ireland. It co-operates with Trinity College as an academic partner. 


Nature is an important medical journal published monthly by the Nature publishing group. It publishes articles on current topics in biomedical research aimed at scientists and the medical profession.