Brain scans show teen girls aged 4 years faster than boys during COVID lockdowns. We asked the researcher what that means long-term.

• A new study found that teen girls' brains aged faster during the pandemic.
• Researchers measured cortical thinning, a natural process that can be accelerated by stress.
• Quicker cortical thinning is linked to higher risks of anxiety and depression.

This week, a new scientific paper sent a ripple through the world of child psychology.

Researchers at the University of Washington published brain scans of teenagers taken three years apart, in 2018 and 2021.

The team expected significant findings, since the second scans were taken after all of the kids had their lives suddenly upended and socially stunted by COVID lockdowns.

They hypothesized that girls would be more impacted, because they're more reliant on peer relationships for emotional support than teen boys. But "we didn't expect it to be as dramatic a difference," lead author Dr. Neva Corrigan told Business Insider.

The average acceleration for teen girls was 4.2 years, compared to 1.4 for boys.

While more research is needed, the study offers a glimpse into the effects the pandemic had on brain development. It comes at a time when teen girls have seen a sharp rise in sadness and hopelessness , often attributed to social media use.

Isolation may have played a role

The original intention of the study was to track typical adolescent brain development, Corrigan, who specializes in MRI data acquisition and analysis, told BI. In 2018, her team took MRI data from 160 adolescents ages 9, 11, 13, 15, and 17, and planned to follow up at a later date.

But after the pandemic, "we realized that we could no longer call this typical development," Corrigan said. "These kids had undergone a huge change in their lives." Her team knew they had a unique opportunity to examine how aspects of the pandemic, such as remote learning , affected the brain.

In 2021, about 130 of the subjects returned for more testing. The team measured cortical thinning, a natural process that usually begins in late childhood and is believed to improve cognitive performance .

The age acceleration was more than double the size in teen girls, and the regions most impacted were all related to social cognition, such as facial recognition and language comprehension.

Because females generally rely more on relationships for emotional support than males, loneliness during the pandemic could have caused teen girls more stress, speeding up their cortical thinning.

Cortical thinning isn't always negative

Corrigan said there's a lot we still don't know about cortical thinning, such as whether it's reversible.

However, she said past studies have shown that accelerated cortical thinning can put people at higher risk for neurodegenerative disorders in old age, such as Alzheimer's and Parkinson's.

It can also increase the odds of developing psychiatric disorders such as depression or anxiety.

At the same time, quicker brain aging isn't necessarily all bad. It's believed that the cortex thins to reduce the effect the environment has on brain development, Corrigan said. If the brain is less vulnerable to external stressors, "that could make these kids a little bit more resilient to stress," she said.

There are still many unknowns

Bradley S. Peterson, a pediatric psychiatrist at Children's Hospital Los Angeles who wasn't part of the study, told The New York Times that it had some limitations. One was that the data came from different subsets of the group, rather than measuring each individual's brain changes.

The study also didn't track the participants' individual habits, so it can't confirm if other elements of the pandemic, such as increased screen time , contributed to quicker cortical thinning.

Corrigan said the biggest takeaway for parents is to be mindful of the potential risks of their teens developing anxiety or depression. "Perhaps they can help stave that off by talking to their kids and providing emotional support for them."