COVID-19 Could Cause Long-Term Brain Tissue Loss

The disease could lead to a loss of gray matter over time. This is what the results of a British study suggest, which draws on data from nearly 800 volunteers. The comparison of their brain scans carried out before and after the infection indeed shows a loss of brain material in certain regions of the brain, even in the case of a mild form of the disease.

This new study, not peer reviewed to date, is based on data from UK Biobank, a health database that includes brain scans taken before the pandemic. In order to assess the impact of COVID-19 on the brain, the researchers invited 394 people who had been infected to perform follow-up scans; they also asked 388 volunteers who had never been sick to perform the same tests for comparison.

However, scientists have observed a significant loss of brain matter, especially in the limbal cortical areas directly linked to the primary olfactory and gustatory system – that is, the brain regions linked to smell and taste. However, most people who are ill have contracted a mild form of the disease, with mild to moderate symptoms or no symptoms; only about fifteen of them required hospitalization.

A significant loss that could promote the onset of dementia

The gray matter is part of the tissues of the central nervous system; it contains most of the neuronal cell bodies of the brain. It includes the brain regions involved in muscle control, sensory perception (smell, sight, hearing…), memory and emotions. In short, it controls the essential functions of our body. Thus, an abnormality in the gray matter of the brain can seriously affect the abilities of an individual.

This is not the first time that researchers have pointed out that an infection due to the coronavirus can damage the brain in the longer or shorter term. Many patients have reported neurological or memory problems after being ill. A study published in April in The Lancet Psychiatry further provided evidence of substantial neurological and psychiatric morbidity within 6 months of infection (estimated incidence was almost 34%); the risks being greatest in patients with severe COVID-19 (the incidence then climbed to 46%).

The results obtained suggested in particular that serious infections of COVID-19 can lead to long-term complications; such as stroke or dementia-like symptoms. A conclusion confirmed by this new study available in a preprint version: the loss of gray matter in regions of the brain linked to memory may increase the risk for these patients of developing dementia in the longer term.

The fact that the study involves participants who have developed a mild or even asymptomatic form of the disease is fundamental, as most of the previous work examining the neurological consequences has only involved moderate to severe cases of COVID-19. ” There is a fundamental need for more information on the brain effects of the disease, even in its mildest form. », Confirm the authors of the study.

Potential long-term effects on memory

Researchers report “significant effects of COVID-19 in the brain,” with loss of gray matter in the left parahippocampal gyrus, left lateral orbitofrontal cortex, and left insula – regions related to the sense of taste and sense of taste. smell, which is consistent with the main symptoms reported by patients.

Longitudinal comparison of the thickness of gray matter in three areas of the brain, between 394 former patients and 388 witnesses. © G. Douaud et al.

In people who had to be hospitalized, scientists noticed an even greater loss of gray matter, especially in the cingulate cortex (linked to decision-making, empathy, emotions), the central nucleus of the amygdala. (the “alert system” of our body, which conditions our behavioral response to fear) and the Ammon’s horn of the hippocampus (linked to memory and spatial navigation). However, no change was detected in the brains of people who were not infected with the virus.

The study authors point out, however, that more research is needed to determine whether or not individuals recovered from COVID-19 are likely to develop long-term problems with their ability to remember events involving emotions. Moreover, they cannot confirm to date whether the loss of gray matter is the simple result of the spread of the virus in the brain – the entry point probably being the olfactory bulb – or if it is a side effect of the disease.

Sources: Reuters and medRxiv, G. Douaud et al.

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