Brain Changes Caused by COVID Could Help Understand Effect on Smell, Memory

New research appears to show the damaging effects of COVID on the brain, including areas associated with smell and memory. The findings could reveal the effects of COVID in greater detail and how the virus spreads through the central nervous system.

Evidence that COVID causes brain-related abnormalities has been provided by previous studies which have focused on hospitalized patients who experienced severe infections as a result of the virus.

The difference between this study, conducted by Gwenaëlle Douaud and colleagues and published in Nature, and those conducted previously is that this study looks at effects in milder cases of COVID. That means it could potentially reveal the mechanism that contributes to brain disease or damage due to COVID.

University of Oxford senior research fellow Max Taquet, whose work involves using brain imaging to characterize and treat psychiatric disorders, said: "This is the first large-scale study to investigate the actual changes in the brain that can occur after a COVID-19 infection.

"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."

Taquet added that it sheds light on this important question by showing that brain regions connected to the "smell center" of the brain can shrink after COVID-19 in some people.

The study's lead author, Douaud, and her colleagues reached their findings by investigating the changes in the brains of 785 COVID patients aged 51 to 81 who had received two brain scans around an average of 38 months apart.

Of this sample, 401 of the UK Biobank participants had suffered a COVID infection between the two scans, and a further 15 of these had been hospitalized.

The team identified a reduction in grey matter thickness in regions of the brain associated with smell and memory.

Patients who had suffered from COVID also seemed to display tissue damage in regions associated with the sense of smell and a reduction in brain sizes. The team compared their results to patients who had suffered from pneumonia, finding the changes exclusive to COVID sufferers.

Chair in neuropsychopharmacology at Imperial College London, David Nutt, believes that this study confirms the opinions of experts in psychiatry and neurology who early in the pandemic predicted COVID would cause neuro-psychiatric complications in some people.

Nutt said: "What we now need is a concerted effort to deal with these brain disorders in the same way as we had a massive engagement with ways to deal with the respiratory impact of the virus for example with the rapid development of ventilators."

Honorary consultant neurologist at the University of Liverpool, Dr. Benedict Michael, told Newsweek: "The bottom line is, this is a very methodologically sound study with pre- and post-COVID controls. But now we need studies to determine what this actually means for people in terms of cognitive function and quality of life etc..."

Professor of Neuropsychiatry, Center for Clinical Brain Sciences, University of
Edinburgh, Alan Carson, urged caution when assessing the results of the study. He said his main concern was that the study was based on a hypothesis that COVID enters the brain via the olfactory nerve. But he pointed out there is now widespread agreement that this is not the case and in fact, direct infection of the central nervous system is rare

Carson also noted that the size and magnitude of the brain changes discovered by the team were small. There were bigger changes discovered in London cab drivers when they took a test to show they knew the city, he said citing a study.

He continued: "The loss of sense of smell seems to be down to damage in support cells in the nose, not the brain. What this study almost certainly shows is the impact, in terms of neural changes, of being disconnected from one's sense of smell."

What also remains unrevealed by this study are the more long-term effects of COVID on the brain and if changes the virus causes can be reversed or if they are permanent. These aspects of COVID infection will, therefore, require further and deeper investigation.

Researcher at Cooper Neurological Institute and Medical School at Rowan University, Cris Constantinescu, told Newsweek: "This is a very interesting study as it is the first one to look at brain abnormalities by quantitative imaging in people who were scanned before and after COVID-19 infection.

"The subtle abnormalities found to demonstrate that the SARS-Cov-2 virus leads to alterations in the brain microstructure, which may explain long-term neurological deficits that persist in affected individuals. It thus adds to the knowledge of the neurological complications of COVID-19."

Brain scan COVID
(Left) a stock image of a brain scan. (Right) an illustration of the COVID virus. Researchers believe they have isolated the effects that COVID has on the smell and memory centers of the brain. Ceren Demir/GETTY