New Studies Shed Light on Brain Fog Connected to Long COVID

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Scientists have catalogued more than 200 different long-term symptoms associated with COVID-19, from fatigue to cardiac problems. Some resemble autoimmune disorders, while others appear to be a result of swarms of microscopic blood clots circulating in the body, including the brain.

Long COVID can develop three to four weeks after the initial infection and can persist for months or even years after a person recovers from a bout with the disease. The more severe a person’s infection, the more likely they are to develop long COVID symptoms.

One of the most common symptoms of long COVID is the mental impairment known as brain fog.

Brain fog sufferers have difficulty thinking and processing information. New research published in July in the journal Cell has found many similarities between long COVID brain fog and the “chemo brain” cancer patients experience while undergoing chemotherapy treatments.

In both cases, the body’s immune system triggers chemicals known as cytokines to protect the body’s systems. Early in the COVID-19 pandemic, some people died from cytokine storms, in which their immune systems overreacted and fatally turned on their bodies.

With brain fog, a cytokine commonly triggered by allergies sets off a chain reaction in the brain and central nervous system that weakens the ability of nerve cells to build new memories and to communicate with each other. The impacts were visible within a week of infection, persisted for up to seven weeks and appeared in people whose infections were so mild they showed no symptoms of COVID-19.

“Given the scale of SARS-CoV-2 infection, this syndrome of persistent cognitive impairment represents a major public health crisis,” wrote the research team led by Anthony Fernández-Castañeda of Stanford University.

Researchers looked at the brains of patients who died during the first wave of COVID-19 infections and also studied the infection’s impact on laboratory mice.

They found that long COVID has its biggest impact on the subcortical white matter, which makes up about half the volume of the brain. White matter acts as the switchboard for the other parts of the brain that control body functions such as movement and speech.

According to the researchers, long COVID unleashes a set of cells that interrupt the formation of new cells in the hippocampus, the area of the brain crucial for memory. The same cells disrupt the creation of brain cells that create myelin, the fatty compound that insulates nerve cells so that, as with telephone wires, signals travel without getting mixed up.

While about a quarter of people who recover from COVID-19 develop long COVID, the discoveries made by Castañeda’s research team suggest that nearly everyone who contracts COVID-19 could be at risk of brain impairment for a time after their infection.

The researchers pointed out that other infections, such as influenza, can provoke some of the same responses in the nervous system. However, only long COVID has been associated with a drop in myelin production — a result that can have serious effects on a person’s nervous system and mental abilities.

“Taken together, the findings presented here illustrate that even mild respiratory infection with SARS-CoV-2 can result in persistent neuroinflammatory changes and consequent dysregulation of neural cell types important for healthy cognitive function,” the researchers wrote.