A startling new study finds that the pandemic prematurely aged the brains of adolescents by at least three to four years. Researchers at Stanford University said that the stress of living though the troubled period physically altered key portions of the brain.

While the American Academy of Pediatrics sounded the alarm on the soaring rates of mental health challenges in this age group, actual neurological evidence of the changes has been scarce, says Axios. By comparing MRI scans of 163 teenagers taken before the pandemic and then afterwards, the scientists found that half the “after” group displayed accelerated signs of aging often seen in children experiencing violence and neglect.

For example, a 16-year-old teenaged girl’s brain post-COVID looked more like that of a 19-or 20-year-old’s before the pandemic. Researchers noted that both the hippocampus, the section of the brain associated with memory and learning, and the amygdala, which processes emotions, were enlarged. The youths were also more likely to report severe anxiety, depression, and internalization of mental health problems.

The study published Thursday in the Journal Biological Psychiatry: Global Open Science was initially started eight years ago to analyze the gender differences in depression among adolescents, says CNN. But the pandemic interrupted the research, and the Stanford team resumed their investigation in 2020, with a new purpose. They decided to study the effects of the pandemic on kids’ developing brains, since they already had initial MRI scans.

Ian Gotlib, lead author of the study, said the research team had expected to find the mental health problems, adding that “the pandemic has not been kind to adolescent mental health.” Gotlib, a professor of psychology at Stanford University and the director of the Stanford Neurodevelopment, Affect, and Psychopathology Laboratory, said the team wasn’t exactly sure what they would find in the MRI scans.

“It’s always interesting to do research like this when you’re not really sure what’s going to happen,” he said. “These effects are interesting and happened pretty quickly.” The team plans to scan the same children later to track their future brain development.

School closures and separation from peers created toxic stress for teenagers, said John Richardson-Lauve, a licensed clinical social worker and mental health director at ChildSavers, a nonprofit focused on trauma therapy for children in low-income communities. He explains this stress alters portions of the brain so that the kids do not process trauma and memories in the same way. While the brain has the ability to bounce back and heal, says Axios, Richardson-Lauve warned that “we can never erase the events of the trauma of the experience. Things never go back to normal after bad things. It’s kind of a myth.”

Gotlib hopes parents and guardians are aware that the lockdowns and school closures may have affected their kids and that the consequences may be lingering.

“Be sure that your adolescent or your teen is getting any help that he or she, that they, might need if they’re experiencing symptoms of depression, anxiety or being withdrawn,” he said, according to CNN.