what to remember from the two studies which confirm cognitive damage up to one year after infection

Is there a link between Covid-19 infection and persistent cognitive problems? This is the question that researchers attempted to answer in two recent studies, notes The World, Friday October 4. They analyzed cognitive deficits, one year after infection, in young patients, for one, and in older patients, for the other.

“For some time we have known that after hospitalization due to Covid-19, many patients have complained of cognitive symptoms, often called ‘brain fog’. But what is less clear is whether there are measurable cognitive impairments in these patients, and if there are, whether the patients recover after a time”explains on YouTube one of the authors, Benedict Michael, professor of neuroscience at the University of Liverpool. Franceinfo summarizes what we can learn from these two studies.

One study carried out on young people, the other on older patients

A first study, published in the scientific journal Nature Medicine on September 23, was performed in the United Kingdom. She followed 351 patients aged 54 on average, specifies The Worldone year after their hospitalization for a severe form of Covid, by comparing them to 2,927 people called “controls”. “We tested their cognitive abilities, took blood samples and performed brain scans”explains on X Greta Wood, research fellow at the University of Liverpool and main author of the study.

The second study, published by a team of London researchers in The Lancet at the beginning of October, focused on “34 volunteers” aged 18 to 30 into whom researchers injected a dose of SARS-CoV-2 a year ago. Eighteen of them subsequently developed an infection, “one without symptoms and the others with mild illness”specifies the study, therefore without long Covid. “Volunteers completed daily physiological measurements and computerized cognitive tasks” in order to“examine the differences between ‘infected’ and ‘inoculated but uninfected’ individuals”. Tasks to assess their reaction time, their level of memory or even attention and distraction.

Twenty years of brain aging

The study on senior patients published in Nature Medicine concludes that“one year after Covid-19, the cognitive deficits measured were equivalent to aging by 20 years” of the brain, explains the author Greta Wood in her video published on X. A 50-year-old person has thus demonstrated cognitive abilities corresponding to those “of a person in their 70s”completes Benedict Michael.

The team of British researchers also detected, in the blood samples, the presence “abnormally high” of markers of brain damage, synonym “an ongoing problem”. Finally, brain scans revealed a “reduction in gray matter volume” in the anterior cingulate cortex, a region “which plays on cognition, attention and emotion”explains Greta Wood. However, the follow-up “demonstrated a tendency towards recovery” in 106 patients, completes the study of Nature Medicine.

Among the youngest, slightly reduced capacities

According to the second study on young patients, published in The Lancet, “Infected volunteers showed cognitive test scores (…) statistically lower than those of uninfected volunteers.” In the tasks that were asked of them, “decreased memory accuracy and executive function are the main factors contributing to decreased scores after infection”write the authors, who specify, however, that the disorders observed are mild.

Executive functions correspond to “mental processes that we implement when of a new situation (to find the solution to a game, solve a math exercise, know how to behave in front of a new colleague, etc.)”explain The World. Symptoms that patients have not detected themselves.

The mechanisms involved are still uncertain

If this confirms previous studies on the consequences on the brain of a Covid infection – like that of Inserm a year ago or that published in Nature in March 2022 – the causes of these attacks on cognitive abilities remain “blurred”write the researchers in The Lancet. “What’s next? We need to better understand the mechanisms at play”therefore exposes Greta Wood. In his article, The World mentions numerous hypotheses: “prolonged cerebral inflammation, destruction or blockage of microvessels, viral persistence at very low level in the brain, autoimmune process”.