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The SARS-CoV-2 coronavirus appears to be capable of generating changes in the human brain. An article published in “Nature” describes the ability of SARS-CoV-2 to modify the human brain, especially in areas associated with smell and memory.
The findings may reveal the damaging effects of Covid-19 and improve understanding of how the disease spreads through the central nervous system.
However, the researchers acknowledge that determining whether these effects can persist long-term or be partially reversed would require more research.
Although evidence suggests that Covid-19 can cause brain-related abnormalities, most studies have focused on hospitalized patients with severe disease and have been limited to post-infection imaging data.
Furthermore, the effects of SARS-CoV-2 on the brain in the milder (and more common) cases are unknown; however, investigation of these cases could reveal possible mechanisms contributing to brain disease or damage.
Researchers from the University of Oxford (United Kingdom) coordinated by Gwenaelle Douaud investigated the changes in the brains of 785 participants of the UK Biobank (ages 51 to 81) who underwent two brain scans, on average 38 months apart, as well as cognitive tests.
Of these, 401 participants tested positive for SARS-CoV-2 infection between their two scans, of whom 15 were hospitalized; the remaining 384 individuals acted as age- and sex-matched controls.
The authors identified several long-term effects after infection (averaging 141 days between participants receiving a Covid diagnosis and second imaging), including a greater reduction in gray matter thickness in the cortex orbitofrontal and parahippocampal gyrus, regions associated with smell and memory.
In addition, the participants who had Covid-19 showed evidence of tissue damage in regions associated with the olfactory cortex, an area related to smell, and an average reduction in the size of the entire brain.
On average, participants infected with SARS-CoV-2 also showed greater cognitive decline between their two scans, associated with atrophy of a region of the brain known as the cerebellum, which is involved in cognition.
The authors also performed a control analysis in people who developed pneumonia that was not related to Covid-19 to show that the changes were specific to the coronavirus disease and not due to the generic effects of contracting a respiratory illness.
David Nutt, from Imperial College London, explains that from the first moments of the pandemic, many psychiatry and neurology experts predicted that the virus would cause significant neuropsychiatric complications in some people. “This paper uses brain imaging to confirm our predictions.”
But does this mean that these cognitive changes are directly caused by SARS-CoV-2, an important and worrying possibility? The researchers give several arguments as to why they think this may be true, although they can’t be sure.
Most worryingly, for Rebecca Dewey of the University of Nottingham, while these kinds of changes are seen after many forms of disease, and even after healthy aging, “the key difference shown here is that they appear to be occurring faster than with aging.
The findings, the researchers conclude, may indicate the degenerative spread of Covid-19either through the olfactory pathways, inflammation of the nervous system, or lack of sensory input due to loss of smell.
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