Research shows that depression increases in difficult environments in young people with a larger left hippocampus

While the mental health crisis is impacting young people of all ages, new research from Northwestern University finds that the presence of a difficult social environment and the absence of a positive social environment predict greater increases in depressive symptoms among young people ages 9 to 11 over a two-year period.

In addition to environment, left hippocampal volume also enhanced the effects of social context, suggesting that youth with larger left hippocampal sizes experience greater increases in major depressive disorder symptoms in challenging social situations.

“Our research not only has implications for future research, but we also hope it will raise awareness among parents, educators, mental health professionals, and policymakers,” said lead author Claudia Haase, an associate professor of human development and social policy in Northwestern’s School of Education and Social Policy (SESP).

“Over the years, the pendulum has swung back and forth between some researchers and practitioners emphasizing the role of nature and others emphasizing the role of nurture. And we’ve really come to realize that we need to look at both and their interactions together.”

The studyin Proceedings of the National Academy of Sciencesunderscores the importance of families, peers, and schools in the development of depression during adolescence, and how variation in neural structure can amplify or attenuate sensitivity to their environment.

The study was first authored by Matías Martínez, a doctoral student at SESP, with senior co-authors Haase and Yang Qu, an associate professor of human development and social policy at SESP. The study, titled “Depressive symptoms during the transition to adolescence: Left hippocampal volume as a marker of social context sensitivity,” is joined by authors including Tianying Cai; Beiming Yang; Zexi Zhou; Stewart Shankman; and Vijay A. Mittal.

“Our study highlights the importance of paying attention to individual differences and how some people are more sensitive to social environments than others,” Qu said. “We should never assume that the same environment has the same impact on everyone. There is no one size fits all.”

The findings

As neuroscience has made great advances in recent years, researchers focused on the sensitivity of the brain in the development of depressive symptoms.

“Previous studies focused on physiological processes or genetic variants, but thanks to the development of neuroscience, we can now look at the role the brain plays in sensitivity to environments,” Martinez said.

“There has long been debate about whether some people are more sensitive to their environment. In this study, we focused on sensitivity to social experiences, both negative and positive.”

The results concluded that the left hippocampus, a brain region primarily associated with memory, learning and how people perceive the world around them, plays a significant role in whether someone becomes depressed when they are in a challenging social environment. A larger hippocampus would lead to an individual being able to better recall an experience or memory.

“It’s one of the most plastic areas of the brain,” Martinez said. “It’s very responsive to the environment, especially in a person’s early years. Our findings show that this brain region plays a role in making young people more sensitive to difficult environments and to the lack of positivity in their life experiences, which leads to symptoms of depression.”

If that brain area is larger in a child, it may lead to that child being more sensitive to social experiences in adolescence, such as family conflict, depressive symptoms of the primary caregiver, peer victimization, parental warmth, and a prosocial school environment.

“Some people assume that we are ‘born this way’ when it comes to the human brain. But the more we learn about the brain, the more scientists understand how open and malleable our brain is, not only in childhood but throughout life,” Haase said.

“Our brains can change in response to the environment we are in. Research shows that this is certainly true for the hippocampus as a brain region.”

The method

The researchers examined two years of longitudinal data from the Adolescent Brain Cognitive Development study. The study, one of the largest studies in the U.S. conducted by 21 research sites across the country, aims to follow a diverse sample of 11,800 children ages 9 to 11 over a 10-year period to observe their cognitive, brain, social and emotional development over time.

“The ABCD study is phenomenal, and we are very grateful to the National Institutes of Health and all the researchers involved for making this possible, and of course all the young people and their families who are participating,” Qu said. “It is the largest long-term study of brain development and child health in the United States.”

The data showed that there was a stronger association between social-experiential environments and MDD symptoms in youth with larger left hippocampal volume. Also, there were no differences in MDD symptoms between individuals with different left hippocampal sizes at low levels of negative and high levels of positive context exposure.

What’s next?

The researchers hope the study will help parents, teachers and policymakers better understand and support young people’s mental health during adolescence. Martinez hopes their extensive research can better explain how children in difficult social environments adapt to their environment in the long term.

“The ABCD Study is such a large project that will continue to track youth development for many years to come,” Martinez said. “It will be exciting to explore what the interplay between environmental exposure, hippocampal volume, and depressive symptoms looks like as our youth navigate their teenage years.”