Brain shrinkage linked to COVID-19

A large study suggests that COVID-19 may shrink the brain's gray matter, primarily in areas of the brain involved in smell and memory processing.

The study, published in the journal Nature, found that the brain structure of people who required hospitalization for COVID-19 had different changes than those who had less severe infections. The structural brain changes that normally occur with age were seen in the study participants, according to Jessica Bernard, a neuroscientist and associate professor at Texas A&M University.

Bernard, who studies how normal age-related brain changes affect people's ability to think and move, said that this definitely is statistically, reliably, above and beyond that.

Why is gray matter gray?

The data from 785 people who had previously contributed brain scans to the U.K. Biobank was included in the new research. Between March 2020 and April 2021, about 4% of these participants were hospitalized for their infections.

The 384 people who did not catch COVID-19 were closely related to the people who did, for example, whether they smoked or had diabetes. The participants who tested negative for the disease had no record of confirmed or suspected COVID-19 from primary care, hospital records or a diagnostic test. The researchers were able to determine how and where their brains differed from their initial Biobank scans after all the participants underwent a second brain Scan.

The real power of the U.K. Biobank is that they have pre- and post-infection images of the participants' brains.

To peer inside the participants brains, the team used a technique that uses a strong magnetic field and radio waves to generate images of soft tissues in the body. The average time before participants caught COVID-19 was 4.5 months. The scans showed that the damage to the brain of people who caught COVID-19 was more extensive than in people who didn't.

The control group showed no tissue loss in the areas of the cerebral cortex that are wrinkled. A region just above the eye sockets, called the orbitofrontal cortex, plays an important role in decision-making by receiving signals from brain areas involved in sensation, emotion and memory. The parahippocampal gyrus surrounds the hippocampus, a seahorse-shaped structure in the middle of the brain that is important for storing new memories.

There are 10 fascinating brain findings.

Shrinkage was most pronounced in these areas, but the control group showed a greater reduction in brain size. The primary olfactory cortex, a structure that receives sensory information from scent- detecting neurons in the nose, has been found to have tissue damage.

The areas that are involved in memory being affected, and connections to the olfactory cortex and the limbic system being involved, are some of the things that are being shown.

Over the course of three years, the control group showed no greater tissue loss or damage than the infectious group. According to a report in the journal Neurobiology of Aging, aging adults lose about 2% to 3% of their gray matter in regions related to memory each year, so additional loss beyond that would be out of the ordinary.

The study authors repeated some of the cognitive assessments the study participants completed to see how their scores had changed. The infections performed worse on the trail making tests than the controls, which are designed to test attention and executive function.

There is a difference in quantitative, cognitive testing, as well as the structural data from theMRIs, she said.

The new study has a few limitations, but it has many strengths. While the authors know which participants developed mild or severe COVID-19, they don't catalog exactly what symptoms each person experienced. It would be interesting to know which participants had symptoms of smell loss or olfactory function, as that might provide clues as to why damage occurred in brain areas connected to the primary olfactory cortex. She noted that a loss of sensory information from the nose could cause the area to become smaller.

The loss of sensory information could explain the damage. They suggested in their report that the coronaviruses may cause an inflammatory immune response that damages the brain.

I don't know if there is anything that suggests one way or another at this point, Bernard said.

I don't think we know mechanistically what's underpinning this She said that based on recent studies, she doesn't think that there is direct invasion of the brain by the coronaviruses.

The mind and body change with age.

She said that a recent study in the journal Cell supports this idea. According to the research, the brain could theoretically be served by a highway into the nose. The cells that the virus infections are embedded in the lining of the nose. The inflammation caused by this infection messes with the function of the olfactory neurons, causing them to produce fewer scent receptors. The authors concluded that this causes smell loss.

It is possible that the mechanism for the observed brain shrinkage is different between coronaviruses. The study only included people who were most likely to have caught the original strain of the disease. She noted that future studies could zoom in on how more recent variants, such as omicron, affect the brain, and others could focus on whether these findings extend to people with long COVID, many of whom report memory problems and brain fog.

The individuals from the U.K. Biobank should be studied to see how their brains change over time.

Bernard asked, "What will we see five, 10, 15 years down the road?" She said that the rate of structural change will be relatively stable after the participants have been bitten. There is a chance that the brain damage caused by COVID could cause cognitive decline at a faster rate than would normally be expected.

Bernard said that this is speculative and that it is too early to know.

Many other research groups are tackling these questions. Individuals who recovered from COVID-19 will be assessed for markers of neurodegenerative disease, including Alzheimer's, with the help of Magnetic Resonance and cognitive assessments.

It was originally published on Live Science.