The brains of teenagers who lived through the Covid pandemic show signs of premature ageing, research suggests. The researchers compared MRI scans of 81 teens in the US taken before the pandemic, between November 2016 and November 2019, with those of 82 teens collected between October 2020 and March 2022, during the pandemic but after lockdowns were lifted. After matching 64 participants in each group for factors including age and sex, the team found that physical changes in the brain that occurred during adolescence – such as thinning of the cortex and growth of the hippocampus and the amygdala – were greater in the post-lockdown group than in the pre-pandemic group, suggesting such processes had sped up. In other words, their brains had aged faster. “Brain age difference was about three years – we hadn’t expected that large an increase given that the lockdown was less than a year [long],” said Ian Gotlib, a professor of psychology at Stanford University and first author of the study. Writing in the journal Biological Psychiatry: Global Open Science, the team report that the participants – a representative sample of adolescents in the Bay Area in California – originally agreed to take part in a study looking at the impact of early life stress on mental health across puberty. As a result, participants were also assessed for symptoms of depression and anxiety. The post-lockdown group self-reported greater mental health difficulties, including more severe symptoms of anxiety, depression and internalising problems. Gotlib said the findings chimed with those from other researchers studying the impact of the pandemic on teens’ mental health. “Deterioration in mental health is accompanied by physical changes in the brain for teens, likely due to the stress of the pandemic,” he said. But it is not yet clear whether the poorer mental health captured in the study is driven by faster brain ageing, or even whether the latter is bad news for teens. “We don’t know that yet – we are starting to rescan all of the participants at age 20, so we’ll have a better sense of whether these changes persist or start to diminish with time,” Gotlib said. “In older adults, these brain changes are often association with reduced cognitive functioning. It’s not clear yet what they mean in adolescents. But this is the first demonstration that difficulties in mental health during the pandemic are accompanied by what seem to be stress-related changes in brain structure.” Michael Thomas, a professor of cognitive neuroscience at Birkbeck University of London, who was not involved in the study, said the research confirmed the struggles that teenagers in particular experienced in the pandemic, with increases in anxiety and depression. But, he added, it was hard to know what differences in the size of brain structure meant for current or future behaviour. “Large-scale measures of the brain don’t tell us about the detailed circuits that drive behaviour. I would say it’s very speculative what, if any, long term consequences there will be, and whether these brain changes will be enduring or fade away.” Thomas also stressed that it was not clear that potential impacts would necessarily be negative, noting some of the accelerated changes reported by the team were also associated with higher performance, such as in intelligence tests. “Famously, London taxi drivers were reported to have larger hippocampuses too,” he said. “In short, these are interesting data to show that the pandemic may have had profound effects on teenagers, enough to be reflected in measures of brain structure; but these data can’t tell us whether negative long-term outcomes are inevitable, or whether the plasticity of the brain will allow this generation to bounce back.”