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How can Covid-19 affect the human brain?

Cognitive impairment from severe Covid-19 is comparable to the decline that takes place between the ages of 50 and 70, according to a recent study from the University of Cambridge and Imperial College London.

Researchers said the degeneration was equivalent to losing 10 IQ points. The results, released earlier this month, were the latest in a series of studies suggesting that Covid-19 is affecting the brain.

The lingering impact of Covid-19 on the millions who have contracted it is still being assessed after more than two years of the pandemic, with few areas of uncertainty as pressing and troubling as the potentially lasting effects on the brain.

Scientists are investigating the exact mechanisms causing neurological effects and whether the symptoms prove transient or the most severe health burdens may still lie in the future.

What are the most striking findings about the effects of Covid-19 on the brain?

Amid a growing body of anecdotal evidence, Alzheimer’s Disease International, a federation of dementia associations, hinted in September that the degenerative effects of the coronavirus could be fueling the “dementia pandemic.” The World Health Organization estimates that the number of people with dementia will increase from about 55 million today to about 80 million by 2030 as the elderly population increases.

Diagram showing how the UK Biobank, a large scale biomedical database, was used to study the effects of Covid-19 on the brain

A study by Oxford University researchers published in March found tissue damage and shrinkage in parts of the brain linked to smell in people who had only mild bouts of Covid-19. Researchers analyzing nearly 800 brain scans from the UK Biobank – one of the world’s largest biomedical databases – found a reduction in overall brain size compared to uninfected people and, on average, greater cognitive decline.

The loss of sense of smell that people noticed in the early days of the pandemic could have been caused by damage to the olfactory nerve, which extends into the brain and mediates this function, according to a study published in JAMA Neurology Last month.

Diagram showing the body's olfactory mechanisms and how Covid-19 could affect them, the results of recent scientific studies show

How concerned are experts?

dr S. Andrew Josephson, Chair of Neurology at the University of California, San Francisco, and Editor-in-Chief of JAMA Neurology, said that people with even mild Covid described symptoms such as mental fatigue, which could be related to the brain. “We’re seeing more and more studies showing changes in the brain that might be related,” he said.

Difficulties in memory, speech and concentration are among a wide range of symptoms that fall under the umbrella term ‘Long Covid’. Defined as suffering symptoms for 12 weeks or more after a Covid-19 diagnosis, medical experts estimate that more than 100 million people are affected.

However, other experts agreed that superficially worrying results may not be as worrying as they first appeared.

“The majority of patients we see clinically have . . . a disturbance in concentration and the ability to direct your thinking,” said Alan Carson, consultant neuropsychiatrist at the University of Edinburgh. “It’s very uncomfortable, but it’s not a permanent neurodegenerative condition — it’s treatable.”

Serena Spudich, a professor of neurology at Yale School of Medicine, said it’s not clear how many changes in the brain are specific to Covid, nor what they mean. “People may lose some gray matter and it may have little meaning in real life,” she said.

What research is underway to find out more?

Research into the link between Covid-19 and dementia is still in its infancy. Scientists said it’s theoretically possible the disease could affect the brain in a similar way to some other viruses.

A 2020 US study found that people with HIV had a 50 percent greater risk of developing dementia. If Sars-Cov-2 “traveled along brain pathways in a similar way to HIV, then it’s possible that Covid infection increases the risk of Alzheimer’s disease,” reflected Dennis Chan, who conducted a cognitive impairment study funded by the long Covid leads UK National Institute for Health and Care Research.

Other scientists said the belief that the virus could reach the broader central nervous system via the olfactory nerve now appears wrong. “It has proven incredibly difficult to infect the brain with coronavirus,” Carson said.

Josephson said researchers were analyzing spinal fluid samples from living patients looking for “unusual antibodies or inflammatory cells” that could shed new light on long Covid.

So far, discouraging precedents from history have not been repeated, experts said.

Clinicians feared the pandemic “could be linked to an encephalitic Parkinson’s disease that had been described after the Spanish flu,” said Anna Cervantes-Arslanian, a neurologist at Boston University School of Medicine.

However, a study she led found that just 0.5 percent of people with severe Covid-19 had meningitis or encephalitis. About 10 percent had altered brain function or structure, according to the study published in the journal in April Explorations in intensive care.

Are new therapies being developed?

Researchers led by Chan are using MRI scans to understand the causes of Covid’s impact on memory, thought speed and decision-making. He said his team will also try cognitive rehabilitation techniques used to treat memory problems after a stroke, such as: B. Assigning tasks to increase mental concentration.

Other scientists are investigating the possibility of new pharmaceutical treatments. Studies are being conducted to examine changes in tissues and organs that cause or are caused by Covid-19 to test treatments.

Josephson said it was unclear whether the brain effects were caused by an overactive immune system or vice versa. But he said if that can’t be determined quickly, it might be best to test drugs that modify the immune system, either decreasing or boosting it, to help those whose symptoms suggest cognitive impairment.

But separating the effects of Covid from other elements only indirectly linked to the virus remains a mystery to researchers.

“The effects of Covid on the brain are real – some people have very discrete, defined conditions and some have things that we don’t understand that well,” Spudich said. “The problem is that there are so many other social factors, pressures and strains related to these pandemic times that this is definitely muddling the water.”

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