After being infected with COVID-19, more and more patients are complaining of the aftereffects of ‘brain fog’, which makes their heads feel dazed. It is noteworthy that results similar to those of cancer patients or Alzheimer’s patients who received chemotherapy appear in the brains of people who experience this phenomenon.
According to foreign media such as the Washington Post on the 29th, Michel Monze, a neuroscientist at Stanford University in the US, recently observed similarities between people who experienced brain fog after being diagnosed with COVID-19 and people with ‘chemo brain’. Chemo brain refers to a cognitive decline that occurs in people exposed to highly toxic drugs such as anticancer drugs or radiation.
The research team observed that the two groups of patients showed similar changes in ‘microglia’, which are related to the immune function of the brain. It is known that these cells malfunction and cognitive function declines in cancer patients who have received chemotherapy. Scholars also hypothesize that Alzheimer’s is caused by a failure of these cells to properly respond to cell damage caused by aging.
Monze’s research is part of an attempt to find similarities between the decline in popularity following COVID-19 infection and mechanisms of other brain diseases, such as chemo-brain and Alzheimer’s. “There are great similarities (between COVID-19 sequelae and other brain injuries),” said Avindra Nas, director of neurological disorders at the National Institutes of Health.
Many studies have been done before on the effect of COVID-19 infection on the brain. There are also reports of a link between COVID-19 infection and Parkinson’s, a degenerative brain disease.
The Van Andel Research Institute in the US analyzed three cases of Parkinson’s disease-like neurodegenerative symptoms after being infected with COVID-19 in 2020. All three had no early symptoms related to Parkinson’s disease before infection and had no family history. In addition, two out of three patients improved their symptoms after taking a Parkinson’s treatment. It is also noteworthy that loss of sense of smell, a typical symptom of Parkinson’s disease, is commonly observed in patients with COVID-19.
Experts believe that COVID-19 infection can cause or worsen neurodegeneration like Parkinson’s. Several recent studies of brain images of confirmed COVID-19 patients have observed marked damage to the nigrostriatal pathway of dopamine. Neurons in this pathway release the neurotransmitter dopamine to coordinate body movements, and when neurodegenerative diseases such as Parkinson’s disease occur, these neurons are degenerated or damaged.
How the COVID-19 virus affects the brain is not yet clear. Researchers pay attention to the role of ‘inflammatory cytokines’, which are immune substances.
Cytokines are substances that our immune system releases for signal transduction in the process of responding to external antigens such as viruses, but when overexpressed, it can cause an immune response that harms our body. Cytokines are known to move through the bloodstream and cross the blood-brain barrier. When exposed to the COVID-19 virus, normal cells can be damaged even if they are not directly infected with the virus due to the action of these cytokines.
Some studies suggest that COVID-19 infection can contract certain structures in the brain.
Recently, a research team led by Professor Gwenel Duod at Oxford University in the UK announced the results of analyzing the brain MRI images of 785 people, including 401 people infected with COVID-19 and 384 people who were not. The researchers compared and analyzed images of people infected with COVID-19 before and after infection with images of non-infected people with similar health and physical conditions.
As a result, it was found that the amount of gray matter in the brain related to memory and smell decreased more in the infected than in the uninfected. In healthy people, it is normal for gray matter to decrease by 0.2 to 0.3% per year with aging. However, the number of COVID-19 infections decreased by 0.7%. Most notably, this gray matter damage was observed even when COVID-19 symptoms were mild.
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Professor Duod analyzed that these abnormal changes observed in the brain appear to be largely related to the loss of smell. However, he estimated that “with time, the detrimental effects of the infection may be mitigated.”
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