Even a mild case of Covid-19 can damage the brain and thinking, scientists have discovered in a study that highlights the disease's worrying impact on brain function.
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Researchers - related brain damage months after infection, including in the area associated with smell, as well as shrinkage equivalent to a decade of normal aging. The changes are presented in a study published in the journal Nature.
The findings represent striking evidence of the virus's impact on the central nervous system. More research will be needed to understand whether the data from the Wellcome Centre for Integrative Neuroimaging at the University of Oxford means that Covid-19 will exacerbate the problem of dementia and other neurodegenerative conditions.
SARS-CoV-2 is widely considered a respiratory pathogen that attacks the lungs. However, it can also cause many neurological complications, including confusion, stroke, and neuromuscular disorders, which manifest during the acute phase of the disease. Other effects such as impaired concentration, headache, sensory disturbances, depression, and even psychosis can persist for months.
To investigate the changes in the brain, neuroscientist Gwenaelle Douaud and her colleagues tapped into the world’s largest database of magnetic resonance imaging. The initial brain MRI scans of 785 volunteers were taken before the start of the pandemic as part of the UK Biobank study , which combines large-scale genomic and detailed clinical data on half a million people.
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A follow-up scan was taken an average of 38 months later. By then, 401 participants had tested positive for Covid. The uninfected remainder served as a control group that was similar to the survivors in age, sex and several risk factors, including blood pressure, obesity, smoking, socioeconomic status and diabetes. The study participants were aged 51 to 81 and were mostly Caucasian.
Among those infected an average of 4.5 months before the second scan, the researchers found greater reductions in gray matter thickness in brain regions associated with smell, known as the orbital cortex and parahippocampal gyrus. The finding may help explain the impaired sense of smell experienced by many patients , as a result of either direct viral damage or inflammation caused by the body's immune response to the virus.
The loss of gray matter, which is the outer layer of the brain, represents degeneration, said Leah Beauchamp, a neuropharmacologist at the Florey Institute of Neuroscience and Mental Health in Melbourne. “This is really concerning,” she said.
The infected group also showed a 0.2%-2% greater reduction in brain size compared to those who were not infected with the virus and also showed greater cognitive decline based on their performance on complex tasks. This was associated with atrophy, or shrinkage, in a specific part of the cerebellum — a region at the back and bottom of the brain — that is associated with cognitive function. The differences between infected and uninfected participants were most pronounced in older people.
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The magnitude of the changes in individual scans was "small" and not visible to the naked eye, Douaud said. A 0.2 percent reduction in gray matter represents about one year of normal aging in an older person's brain. A 2 percent reduction represents about 10 years of aging.
The research suggests that brain changes can occur after infection , even in people who did not require hospitalization, said Joanna Hellmuth, a neurologist and assistant professor at the University of California, Berkeley. “Future research efforts can help us understand whether these brain changes are clinically relevant and whether they are related to specific neurological issues after Covid,” she said.
