Not long ago, Mark Chiverton, a 33-year-old in the U.K., noticed he was making a lot of silly mistakes. He’d mix up words when writing emails, or blank on a basic term while talking to his wife. None of these slip-ups were all that concerning on their own—but they were happening frequently enough that Chiverton worried he was, to put it bluntly, “getting dumber.”

“At first I thought, ‘Maybe it’s just general aging, or maybe I bashed my head and didn’t realize it,’” he says. But eventually, a thought occurred to him: could COVID-19 be the reason for his mental slips? Chiverton thinks he caught the virus in early 2020, before tests were widely available, and he knows for sure he had it in 2022. Though he has no lingering physical effects from those infections (and has periods of time when his brain cramps get better), he sometimes wonders whether those mental slips are mild signs of Long COVID, the name for chronic symptoms following an infection.

He’s not alone in experiencing these problems—and he may not be wrong that COVID-19 is to blame. In the U.S. alone, about a million more working-age adults reported having serious difficulty remembering, concentrating, or making decisions in 2023 compared to before the pandemic, according to a New York Times analysis of Census Bureau data.

Every mental mistake isn’t cause for concern, says Andrew Petkus, an associate professor of clinical neurology at the University of Southern California’s Keck School of Medicine. Blunders like forgetting why you walked into a room or spacing out on an appointment can be totally normal parts of being busy, distracted, often under-rested humans. Even though you likely did those things before and brushed them off as nothing, they may seem more significant in the wake of a life-altering event like the pandemic. “If we didn’t have COVID, you might have still forgotten,” Petkus says.

Still, it’s not outlandish to think the pandemic has had an effect on our minds, says Jonas Vibell, a cognitive and behavioral neuroscientist at the University of Hawaii at Manoa. Vibell is currently trying to measure post-COVID inflammation and neuronal damage in the brains of people who report symptoms like brain fog, sluggishness, or reduced energy. When he began publicizing the study, he says, “I got so many emails from lots of people saying the same thing”: that they’d never fully bounced back after the pandemic.

But why? It’s probably a mix of things, Vibell says. The SARS-CoV-2 virus can affect the brain directly, as many studies have now shown. But the pandemic may have also affected cognition in less-obvious ways. Months or years spent at home, living most of life through screens, may have left a lingering mark. Even though society is now mostly back to normal, the trauma of living through a terrifying, unprecedented health crisis can be hard to shake.

Your brain on SARS-CoV-2

It’s clear by now that SARS-CoV-2 is not just a respiratory virus, but also one that can affect organs throughout the body—including the brain. Researchers are still learning about why that is, but leading hypotheses suggest that SARS-CoV-2 may cause persistent inflammation in the brain, damage to blood vessels in the brain, immune dysfunction so extreme it affects the brain, or perhaps a combination of all the above. Studies have even found that people’s brains can shrink after having COVID-19, a change potentially associated with cognitive issues.

COVID-19 has been linked to serious cognitive problems, including dementia and suicidal thinking. And brain fog, a common symptom of Long COVID, can be so profound that people are unable to live the lives and work the jobs they once did. But COVID-19 also seems able to affect the brain in subtler ways. A 2024 study in the New England Journal of Medicine compared the cognitive performance of people who’d fully recovered from COVID-19 with that of a similar group of people who’d never had the virus. The COVID-19 group did worse, equivalent to a deficit of about three IQ points.

That’s not a dramatic difference. Our cognitive abilities naturally fluctuate a little from day to day—and in a July interview with TIME, study co-author Adam Hampshire, a professor of cognitive and computational neuroscience at King’s College London, said a three-point IQ difference is “well within” the range of that normal fluctuation, so small that some people might not even notice it.

But could such a drop be enough to lead to, say, extra typos and absentmindedness? Maybe. In Hampshire’s study, people who’d had COVID-19 consistently performed worse on cognitive tests than people who hadn’t.

If the brain suffers “mild but ubiquitous” changes after an infection, Vibell says, those effects could feasibly “impact the brain, behavior, and social behavior in so many subtle, but maybe [cumulatively] quite bad, ways.”

Beyond the virus

Even for the lucky few who have never been infected, living through a pandemic can impact the brain.

For a recent study in PNAS, researchers conducted pairs of MRI brain scans on a small group of U.S. adolescents: one in 2018 and one in either 2021 or 2022. Over those years, they observed a notable thinning in parts of the kids’ (and especially girls’) brains, including those that control social cognition tasks like processing facial expressions and emotions. Although the researchers did not analyze the effects of SARS-CoV-2 infections, they concluded that the stress of living through pandemic lockdowns was likely to blame for the change, which they likened to an extra four years of brain aging for girls and an extra year for boys.

Stress and trauma have well-documented effects on the brain. Plenty of studies show that people who experience trauma tend to be at greater risk for cognitive decline as they age. Stress can also impair someone’s ability to think clearly, reason, and remember, studies suggest.

“COVID was a generational traumatic event,” says USC’s Petkus. “Everybody was exposed to it.” It’s feasible, then, that the population at large is suffering some of these side effects from trauma and stress.

Even beyond the mental toll of living through a scary and unsettling time, many people had to abandon habits that are good for the brain—things like socializing, staying physically and cognitively active, and seeking out novel experiences—when they were stuck at home early on, Petkus says. It’s too soon to say whether that dramatic but short-lived period will have long-lasting effects—but four years after the virus emerged, some things are still not as they were.

For example, student test scores are recovering but have still not bounced back to pre-pandemic levels; declines have been particularly dramatic in low-income school districts as well as those that had remote learning in place for a long time, says Sean Reardon, a professor at Stanford University’s Graduate School of Education and one of the leaders of the Education Recovery Scorecard, a research project focused on pandemic learning loss. The long recovery process probably speaks to a combination of things, Reardon says: not only did kids miss in-person school for a while, they also experienced seismic disruptions in their lives, endured a period of significant stress and anxiety, and are now being asked to learn new material in school while also making up for pandemic-related learning gaps.

“Falling behind on your math skills or your reading skills is not really about a change in your intelligence,” Reardon says. “It’s a change in your skills, how much you’ve had the opportunity to learn.” 

It’s hard to say whether the same trends appear among adults, because grownups aren’t taking standardized tests every year at work. Adults were certainly exposed to the same mix of stress, trauma, boredom, and isolation as kids—but Reardon says his hunch is that adults may have an easier time rebounding, since they’ve already developed the skills they lean on to perform complex tasks.

Returning to normal

“There might have been a shock for a couple years, but things are getting back to normal,” Petkus agrees. 

Those who feel like their minds melted a little during the pandemic can likely benefit from adopting or resuming the kinds of brain-boosting habits that fell by the wayside during Netflix-fueled lockdowns, like social interaction and mental and physical exercise, Petkus says. Even the effects of stress and trauma can often be counterbalanced with social support and healthy coping strategies, he says. People who recover well from hard events sometimes even experience what’s known as post-traumatic growth, a blossoming of their mental and emotional health after a difficult period.

It’s harder to say whether brain changes that result directly from SARS-CoV-2 infections are reversible, as researchers are still studying that question. But there are some positive signs. Some of the potential causes of chronic brain fog—like persistent inflammation or damage to blood vessels—are theoretically reversible with the right treatments.

Even in Hampshire’s study on post-COVID IQ differences, there was cause for optimism. Hampshire’s team found that people with Long COVID symptoms were, on average, about six IQ points beneath people who’d never had COVID-19. But those whose Long COVID symptoms resolved over time also saw their cognitive scores improve.

That finding is “quite positive,” he said. “There could be some hope for people who are struggling.”