Inside Neuroscience: Scientists Examine How Brain Structure and Function Change During Adolescence
As many neuroscientists know, adolescence is a dynamic time of change in the brain. Research is now revealing active growth of teenagers’ social skills and decision-making processes during this period.
“Adolescence marks an important and dynamic time in brain development, both in terms of changes in connectivity and specialization,” said Jay Giedd of the National Institute of Mental Health (NIMH), who moderated a press conference on adolescence at Neuroscience 2012. As a result, adolescents represent a fascinating subject for neuroscientists to study.
During the press event, scientists described emerging research revealing the ways brain structure and function change during adolescence, and how early life experience influences behavior during this period.
Social Brain Continues to Develop During Adolescence
Social cognition equips people with the necessary skills to understand and interact with one another. While social skills continue to develop during adolescence, it was not previously well-understood how the regions of the brain related to social cognition develop during this time.
To examine these changes, press conference presenter Kathryn Mills and colleagues at the UCL Institute of Cognitive Neuroscience in London and the NIMH took multiple brain scans of nearly 300 individuals between ages 7 and 30. The researchers found decreases in gray matter volume and thickness in four regions of the “social brain” (medial prefrontal cortex, temporoparietal junction, posterior superior temporal sulcus, and anterior temporal cortex) between adolescence and adulthood.
“The ongoing development of the social brain during adolescence possibly helps adolescents navigate the new social demands they encounter after the onset of puberty,” Mills said.
Emotional Experiences Early in Life Influence Response to Reward in Late Adolescence
The brain’s reward system undergoes significant changes during the transition from childhood to adulthood. This period presents enormous opportunity for the brain, but also marks a period of increased vulnerability, with the emergence of several psychiatric disorders including depression.
Press conference presenter Erika Forbes of the University of Pittsburgh described how she and her colleagues studied whether emotional experiences early in life alter the brain’s response to reward in late-adolescence. As part of the Pitt Mother-Child project, Forbes and her colleague Daniel Shaw tracked the behavior of more than 100 young men over a 10-year period, beginning at age 10. They assessed mental health and observed the interactions between the young men and their mothers. At age 20, the men received an fMRI scan while performing a monetary reward task.
The researchers discovered that men who reported depression at any point in their lifetime had decreased activity in the ventral striatum and increased activity in the medial prefrontal cortex when performing the reward task compared with individuals with no history of depression. Additionally, men who displayed more positive emotions toward their mothers as children showed greater activity in the amygdala when performing the reward task.
“We’re reporting a long-term association between behavior and brain function — in this case, up to 10 years,” Forbes said. The findings suggest “positive family relationships and mental health could promote brain development.”
Cognitive Stimulation Early in Life Predicts Brain Structure in Late Adolescence
Animal studies have shown that early environment can have long-term consequences for how the brain develops and functions. However, less is known about how early life experience affects the human brain. Press conference presenter Martha Farah described how she and others at the University of Pennsylvania examined whether early experience might influence brain structure later in life.
For the study, the researchers visited the homes of more than 60 children at age 4 and again at age 8. There, they assessed the level of cognitive stimulation (i.e., presence of toys that teach numbers and letters or 10 or more books). The researchers also evaluated the degree of nurturing displayed by the parent toward the child. At age 19, the study participants received an MRI.
Farah’s group discovered that the degree of cognitive stimulation in the home environment at age 4 predicted the thickness of several regions of cortex in late adolescence. Neither the degree of cognitive stimulation at age 8 nor the parental nurturance at either age predicted cortical thickness later in life.
Farah cautioned that while findings cannot speak to causality, “the value of this research is that it’s a first step at looking at how early life experience impacts structure later in life.”
Early Diet May Influence Risk of Depression in Late Adolescence
Early diet also influences healthy brain development in adolescence, noted press conference presenter Christopher Butt of DSM Nutritional Products in Boulder, Colorado.
Although previous work suggests that diets rich in omega-3 fatty acids enhance mood in adults, it is unclear whether exposure to specific omega-3s during gestation alone is enough to produce these effects or whether it is required throughout the lifetime. Butt’s group fed pregnant rats and their offspring a diet that either contained the omega-3 fatty acid docosahexaenoic acid (DHA) or did not. Later, the researchers measured depressive-like behaviors in the offspring before and after puberty using the forced swim test.
While exposure to DHA had no bearing on behavior in the animals before puberty, after puberty, the animals on a lifelong DHA diet displayed a lower amount of depressive-like symptoms than rats that had no DHA in their diets. Additionally, rats fed DHA-rich diets had higher levels of brain-derived neurotrophic factor (BDNF) and serotonin — biomarkers that are typically low in people with depression. According to Butt, the study points out the important roles that diet and DHA likely play in brain development and health throughout the lifetime.
Teens are Willing to Wait for Larger Reward
While data presented during the press conference suggests that early diet and life experience can set the brain on a developmental trajectory during adolescence, press conference presenter BJ Casey of Weill Cornell Medical College described her interest in what goes on in the minds of teens when they are “in the heat of the moment,” and how their heightened sensitivity to reward drives them to act out in ways they might otherwise not.
Curious whether there might be a way to take advantage of teens’ sensitivity to reward to help guide them to better choices, Theresa Teslovich, Casey’s graduate student, and her colleagues asked teens and adults to perform a task in which they could earn a high or low number of points by correctly detecting the direction of dots moving on a screen. They found that teens spent more time deliberating before making a decision if greater point values were at stake. In contrast, adults made decisions faster as reward values increased. fMRI scans revealed the longer adolescents were willing to wait before making a decision, the greater the activity in the ventral striatum of the teens.
“What’s interesting is this same system, the reward system … can drive behavior in an impulsive way and it can also drive behavior in a very motivated, decisive way. It depends on what brain regions it’s talking to,” Casey said. “We think that these findings have huge implications for interventions for teens.”
Studies examining the development of the adolescent brain are just beginning to offer new details about how early life experiences can set teens on the right developmental path and encourage them to be more thoughtful about the decisions they make. During the press event, panelists expressed optimism that future studies may one day help scientists better understand how genes and experience shape the brain, and offer more insights for teens, caregivers, and teachers.