he COVID-19 pandemic affected people of all ages and from different walks of life, but just how much did it impact adolescents? In a new study, a team of researchers found that it may have physically altered teens' brains.

For their study, published Thursday in Biological Psychiatry: Global Open Science, the researchers compared the brains of teens before the pandemic (pre-COVID) and after experiencing the pandemic-related shutdowns (peri-COVID).

The researchers weren't initially aiming to make the comparison, according to the news release from Stanford University. Before the pandemic, the researchers were conducting a longitudinal study on the effects of early life stress on adolescents in the San Francisco Bay Area, wherein they were invited for assessments every two years.

However, the study — just like most things across the world — came to a halt when the pandemic hit. As such, the researchers then had to have a "hard restart," study first author, Ian Gotlib of Stanford University, said as per the news release.

This, however, gave them a unique opportunity to look at the impacts of the pandemic on adolescents' brains.

"(I)t is not clear whether youth who lived through the pandemic and its shutdowns are comparable psychobiologically to their age- and sex-matched peers assessed before the pandemic," the researchers wrote.

To find out, the researchers compared the peri- and pre-COVID participants, matching them "as closely as possible" in terms of age and sex.

Indeed, they found that the pandemic appeared to have physically altered the adolescents' brains. Those who experienced the pandemic shutdowns had "reduced cortical thickness, larger hippocampal and amygdala volume, and more advanced brain age."

Their internalizing of mental health problems was also more severe.

Although it's quite natural for people's brains to change as they age, the results of the scans show that the process appears to have "sped up" in the teens they scanned after the shutdowns. The features in those teens' brains, researchers say, "are more typical of individuals who are older or who experienced significant adversity in childhood."

According to the researchers, this shows that the pandemic not only affected these young people's mental health but also affected their brain maturation, with the features indicating "older-appearing brains."

This, they say, is something that researchers conducting longitudinal studies halted by the pandemic may want to take note of.

The question now is whether the changes are permanent or merely temporary, Gotlib said, noting that there's also the question of whether their chronological age will "eventually catch up to their 'brain age,'" and how this may affect them in the long run.

"(I)t is important that we continue to follow and assess individuals who were recruited and assessed prior to the pandemic; this type of research offers the strongest possibility for us to examine the effects of a major stressor experienced on a global scale," the researchers wrote.