The possibility that a Covid infection could damage your brain is terrifying. Scientists have established that long Covid often manifests itself with neurological changes — brain fog, memory problems, fatigue. And some researchers have found changes in the brain after even mild cases of the virus. Every time I go on Twitter I see another horrible personal anecdote, often reflecting changes in brain processing speed and an increase in confusion and errors.  There’s also potentially a deep societal and economic cost. One Brookings Institution report estimated that perhaps 4 million Americans have been unable to work due to long Covid; some of these sufferers have blamed brain fog for ruining their ability to think. What will happen to human beings if our brainpower gets blunted? It’s enough to make you wonder: Even if I feel fine, is my brain really unscathed?  The scientific paper that’s most often cited in media scare stories on brain damage and Covid came from the Wellcome Center for Integrative Neuroimaging and Oxford University. Researchers there made clever use of brain scans taken from 785 people before the pandemic. By bringing them back some months into the pandemic, the scientists could compare those who’d had Covid with those who hadn’t. All the brains showed small fluctuations, but on average, the previously infected showed a small decrease in the amount of grey matter, concentrated in the region that governs smell and memory.  The researchers noticed a similarity to changes associated with aging — and that led to headlines saying that Covid ages your brain by up to a decade. But there were big unanswered questions raised by that study — ones I wrote about when it published last March.  The brain difference was an average — some people’s brains aged 10 years, while others only seemed a year older. And it’s possible that some people recovered from Covid with no changes in their brains. The researchers noted that the brain changes were more pronounced in older people and those with more severe infections — ones that required a trip to the hospital. The paper didn’t connect the brain changes to any experience of long Covid, and neurologists I spoke with at the time said it’s hard to know what’s clinically significant. And there was no way to know back then whether these changes were likely to be permanent.  The researchers declined my requests for an interview, but I did find other experts who had jumped in with their own studies. Neurobiologist Maria Mavrikaki of Beth Israel Deaconess Medical Center in Boston had become fascinated by the imaging study and pointed out that the researchers also saw one form of cognitive decline in Covid patients over 60 — an increase in the time it took to complete a connect-the-dots puzzle. “These individuals that are recovered from mild Covid demonstrate cognitive decline and they are losing gray matter in the brain,” she said. The changes might not be permanent. But they are still worrisome. Mavrikaki pointed to another study, which was carried out in France in 2020 using PET scans performed during Covid infections, after recovery, and six months later. The subjects all improved, although not everyone recovered completely. She and her colleagues tried a different approach — looking for changes at the molecular level by studying the brains of people who died from Covid and comparing them to brains of people who died from other causes. They published their results last December in Nature Aging.    She said the brains, which come from a source called NeuroBioBank, could be categorized so she could compare those who died from Covid with those who suffered no psychological or cognitive diseases when they died.  The Covid-infected brains showed activation in genes associated with immune responses, and decreased expression of genes associated with cognition, learning and memory. Worse still, the changes resembled those other researchers had found for people who showed what she called “low cognitive performance” before they died.  How scared should we be? She said it’s not like 100% of people who get Covid — especially a mild case — will see cognitive decline. “But it is a possibility for a percent of them,” she said.  There are various mechanisms scientists are studying to understand how Covid might cause brain damage, including infection in some brain cells, and an errant immune response that stays switched on after the infection is gone.  At the National Institutes of Health, neurologist Avindra Nath has also been using imaging to study Covid and the brain. He specializes in the way different viruses affect the brain — from HIV to Ebola.  When I stopped by his lab earlier this month, he estimated that long-term neurological problems affected about 10% of people before vaccines were available, and some smaller percentage of people now. That’s bad — the meaning of the word decimate is to take out one of ten soldiers. But there’s still hope that people are either slowly recovering or will respond to one of the treatments that’s being developed. He’s launching a clinical trial that will use an antibody treatment in an attempt to tamp down excess inflammation in people with long-term neurological problems.  What about those of us who feel okay but had a bout with Covid despite getting vaccinated? If you feel fine, he said, you probably are fine. It’s a roll of the dice and we’re the lucky ones. He said people’s brains can show age-related degeneration from all kinds of factors including injuries, alcohol consumption and possibly other viruses, such as flu. So maybe the root of my anxiety comes down to the awareness that so much hinges on this three-pound organ that can be so easily inflamed by viruses that are all around us, as well as damaged from minor injuries and youthful drinking binges. That mild case of Covid might have been less damaging than getting the flu a couple of decades ago, drinking too much and getting minor bumps playing sports when I was younger and more reckless. The best we can do is be thankful we’re still alive and functioning, get a flu shot as well as Covid boosters, wear a helmet for dangerous sports, and don’t waste too much mental energy agonizing about the past. Bloomberg