The pandemic's impact on teens has been profound, with numerous studies reporting challenges with their mental health, social lives, and more.
Now, a new study suggests that these phenomena caused some adolescents' brains to age much faster than normal: an average of 4.2 years faster in girls and 1.4 years faster in boys, according to the research published Monday in the journal Proceedings of the National Academy of Sciences.
By being the first to provide detailed information on differences in aging based on sex, the study adds to existing knowledge from two previous studies on the Covid-19 pandemic and accelerated brain aging in adolescents.
"The findings are an important wake-up call about the vulnerability of the teenage brain," said senior study author Dr. Patricia K. Kuhl, the Bezos Family Foundation Endowed Chair in Early Childhood Learning and co-director of the Institute for Learning and Brain Sciences at the University of Washington in Seattle, via email. "Teens need our support now more than ever."
Significant social-emotional development occurs during adolescence, along with substantial changes in brain structure and function. The thickness of the cerebral cortex naturally peaks during childhood, declines steadily through adolescence, and continues to decline throughout a person's life, the authors wrote.
The researchers originally wanted to track the normal development of adolescent brains over time, starting with MRIs the authors performed on the participants' brains in 2018. They planned to scan them again in 2020.
The pandemic delayed the second MRI by three to four years, when the 130 participants in Washington state were between the ages of 12 and 20. The authors excluded adolescents who had been diagnosed with a developmental or psychiatric disorder or who were taking psychotropic medications.
The team used the pre-pandemic MRI data to create a "normative model" of how 68 brain regions were likely to develop during typical adolescence, which they could compare to the post-pandemic MRI data and see if it deviated from expectations. This normative model is analogous to the normative growth charts used in pediatric clinics to track height and weight in young children, the authors said. It has also been used by other researchers to study the effects of circumstances or conditions such as socioeconomic disadvantage, autism, depression, attention deficit hyperactivity disorder or traumatic stress.
The study revealed accelerated cortical thinning in the post-pandemic brains of teenagers - occurring in 30 brain regions across both hemispheres and all lobes in girls, and in only two regions in boys. The prevalence of the thinning was 43% and 6% of the brain regions studied in girls and boys, respectively.
The study "is not a major revelation, as the authors acknowledge," but it does add to our knowledge on the topic, Dr. Max Wiznitzer, a professor of pediatrics and neurology at Case Western Reserve University School of Medicine, said via email. Wiznitzer was not involved in the study.
How Adversity Affects the Brain
The study has a number of important limitations, including the fact that lead author Kuhl submitted the study to the journal. This means that she was also an editor of the study and, with limitations, could choose who would peer-review the study.
And because everyone was affected by the pandemic, the authors had no control group. So they had to use normative models to approximate what normal controls would have been, Wiznitzer said - "which is not as good as real controls, but probably the best they can do."
The authors also did not have data on the jobs, financial or food security of the participants' families, or on the participants' exercise, sleep or eating habits, they said. It is also unknown whether the fact that the participants may have had Covid-19 could have contributed to the findings.
"Their study is good, but even then the sample size is probably not large enough to say that the sex difference in brain aging is a reliable finding," said Dr. Ian Gotlib, author of a 2022 study on the topic and director of the Stanford Neurodevelopment, Affect, and Psychopathology Laboratory at Stanford University, via email.
However, "after reading this paper, we examined the sexual differences in the data we used in our study - the same direction of sexual differences as the authors reported, but not statistically significant with our slightly smaller sample," added Gotlib, who was not involved in the study.
The regions with the greatest acceleration in thinning in girls are linked to social-cognitive functions, such as recognizing and processing faces and expressions; processing social and emotional experiences; the ability to have empathy and compassion; and language comprehension, the study found. The affected regions in boys' brains are involved in processing objects in the visual field and faces.
Based on previous research, the authors believe the findings may be due to a phenomenon known as the "stress acceleration hypothesis." This hypothesis states that in a high-stress environment, development may shift toward earlier maturation to protect emotional circuits and regions of the brain involved in learning and memory - thereby reducing the damage of adversity on structural development.
There are also reports of correlations between salivary cortisol levels and cortical thickness in the frontal lobe in adult humans. Sex differences could be due to the differential effects of stressors on boys versus girls, based on what is important to each, the authors said.
What you can do
Another factor researchers don't yet know is whether these effects on the brain are permanent, Kuhl said.
"The brain doesn't recover and it doesn't get thicker, we know that, but one measure of whether teens show recovery after the pandemic is over and social normalcy is fully restored is whether their brains are thinning more slowly," Kuhl added. "If that were the case, we could say that teen brains showed some recovery. That's a study we can actually do in the future."
It's crucial to make sure young people are supported in their mental health, Gotlib said. Encourage quality personal time, limit social media use and watch for behavioral changes that reflect a shift in mental health or mood so you can intervene as early as possible, Wiznitzer said.
It is important to recognize that while the "pandemic is largely over," its effects are still being felt, Gotlib said.
"A full return to 'normal' may never happen," Kuhl said via email. "These are all powerful reminders of human fragility and the importance of investing in the science of prevention and preparation for the next (inevitable) pandemic."
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