But can it cause the brain to shrink and are the changes permanent?
Here’s what you need to know.
How does Covid impact the brain?
Changes to the human brain following Covid-19 have been described in a new paper.
Researchers investigated the changes in the brains of 785 UK Biobank participants aged 51–81 who had two brain scans, on average 38 months apart, and also underwent cognitive tests.
The research, titled Sars-CoV-2 is associated with changes in brain structure in UK Biobank and carried out by Gwenaelle Douaud from the University of Oxford and others, appeared in the Nature journal.
The UK Biobank is a large database that includes genetic and health information on half-a-million people living in the UK.
A total of 401 participants tested positive for infection with Covid between their two scans, with 15 of these admitted to hospital.
The authors of the study identified various long-term effects following infection, with an average of 141 days between participants receiving a Covid diagnosis and the second scan.
Effects on the brain included a greater reduction in grey matter thickness in the orbitofrontal cortex and parahippocampal gyrus, which are regions associated with smell and memory.
Those who had Covid displayed evidence of tissue damage in regions associated with the olfactory cortex - an area linked to smell - and an average reduction in whole brain sizes.
The participants who were infected with Covid also showed on average a greater cognitive decline between their two scans. This was associated with the atrophy of a brain region known as the cerebellum, which is linked to cognition.
What else did the research discover?
Dr Max Taquet, NIHR Oxford Health BRC senior research fellow, University of Oxford, said that this is the first large-scale study to investigate actual changes in the brain that can occur after contracting Covid.
He added: “It is well established that Covid-19 infection is associated with subsequent risks of neurological and psychiatric problems in some people including brain fog, loss of taste and smell, depression, and psychosis.
“But why this occurs remains largely unknown. This study starts to shed light on this important question by showing that brain regions connected to the ‘smell centre’ of the brain can shrink after Covid-19 in some people.”
Brain fog can include poor concentration, feeling confused, thinking more slowly than usual, fuzzy thoughts, forgetfulness, lost words, and mental fatigue.
Dr Taquet said these brain changes were not observed in every patient and were mostly subtle, but the findings “might help explain why some people experience brain symptoms long after the acute infection”.
“The causes of these brain changes, whether they can be prevented or even reverted, as well as whether similar changes are observed in hospitalised patients, in children and younger adults, and in minority ethnic groups, remain to be determined,” he added.
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