Increasingly, the courts are turning to neuroscientific data as additional evidence in making legal decisions. From examining questions of impaired ability to even issues of diversity and bias, neuroscience and the law are intersecting more frequently. A key question often at stake is at what age is are people’s brains “mature enough” to make and be responsible for their own decisions.
This question is also at the center of work by Leah Somerville of Harvard University. Somerville studies the adolescent brain to understand how its development affects behavior. Recipient of the CNS Young Investigator Award, she will present work at the CNS conference in San Francisco next month that suggests that the adolescent brain is uniquely “tuned” to particular types of motivation, such as rewards and social information. Exactly how that influences teens’ behavior depends on the goal at hand. For example, being driven by a reward such as going to a party with friends could lead to increased risky behavior – such as driving too fast or texting while driving. However, if the reward is, say, winning a speech competition, the motivation could lead to positive, innovative behavior.
Somerville spoke with CNS about the work she will be presenting at CNS 2017, including what makes the adolescent brain unique, the role neuroscience should play in policymaking, and new datasets on the horizon.
CNS: Why do you personally study the adolescent brain?
Somerville: Adolescence represents a precarious phase of the lifespan, marked by simultaneous achievement and vulnerability. My lab’s focus on the cognitive neuroscience of human adolescence reflects three intertwined research goals: to bolster fundamental understanding of human neurodevelopment, to inform relationships between circuit-level brain development and behavioral outcomes, and to gain insight into mechanisms of health risks that emerge during adolescence.
CNS: Briefly, what is most unique about the brain of adolescents compared to those of people younger and older?
Somerville: The adolescent brain, although it’s the same overall size as the adult brain, is still undergoing a host of changes that we believe influence adolescent-typical behavior. There are continuing changes in brain structure, neuroendocrine changes as a result of pubertal hormones, and also changes in brain function and connectivity. Our work has revealed that the connectivity amongst brain systems is continuing to become more refined throughout adolescence, and that these late shifts in connectivity influence adolescent typical behavior such as cognitive control, learning, and decision making.
CNS: Your work and others are suggesting that biased motivational drives are at work in influencing risky behavior for teens. Briefly, how do you characterize these biased motivational drives?
Somerville: We are really interested in the impact of motivational cues on adolescent goal-directed behavior. It’s a complex puzzle because on one hand, what is “motivating” to a person changes across development; on the other hand, these kinds of cues are encoded by the brain with different levels of robustness across development. During adolescence, rewards, high arousal, and social information seem to be especially motivating in terms of propelling approach behavior. Our work has shown that continued development of striatocortical circuit function and connectivity mediates the robust influence of motivational signals on adolescents’ choices and actions. Depending on the goal at hand, this can either be helpful or hurtful for adolescent goal-directed behavior.
CNS: How is this view different from the previous idea that risky behavior in adolescence is tied to immature cognitive control?
Somerville: Cognitive control processes are critically intertwined with a host of other processes that, together, shape goal-directed behavior and decision making. With that in mind, the slow-and-steady development of cognitive control throughout adolescence is just one of several components of adolescent risky behavior.
CNS: How do you define neurobiological maturity? Do you define it? If not, why?
Somerville: The concept of “brain maturity” is extremely complex and the field has not yet arrived at a consensus on the necessary or sufficient conditions for a brain to be mature. Different measurements of the brain – structural, functional, and connectivity – hit developmental “plateaus” at different times and to complicate things further, these trajectories are regionally and network-specific. We think of development as a progressive process that need not have a clear endpoint, so we are not that troubled by a lack of consensus. However, neuroscientists are being pulled into conversations about brain maturity given the interest of policymakers and the public at large.
Neuroscientific evidence is one piece of a much larger puzzle, and I believe that we should be very cautious to prescribe concrete policies based on it.
CNS: What role would you like to see this work play in policymaking and the law?
Somerville: The concept of biological maturity intersects with a host of societal issues centered on decision making. For example, when should people be considered ready to make their own healthcare decisions? And, when should people be held fully responsible for crimes they commit? While neuroscience has definitively shown that the brain continues to develop well past the legal definition of adulthood in the United States (age 18), there is still much to be learned about how this prolonged neurodevelopment shapes decision making in these domains. Neuroscientific evidence is one piece of a much larger puzzle, and I believe that we should be very cautious to prescribe concrete policies based on it. Clearer answers may be possible in the future with larger and more definitive datasets, cognitive neuroscience research that links neurodevelopment with adolescent-typical decision making, and clearer theoretical consideration of the concept of “maturity.”
CNS: What are the next steps for your work?
Somerville: Right now, we are very excited about being a part of the Human Connectome Project in Development; we have just started to collect data. The project will produce a dataset of more than 1,700 scan sessions focused on brain connectivity development in 5- to 21-year-olds. Large studies like these will allow us to take a closer look at the foundational mechanisms of neurodevelopment, such as the influence of age, pubertal hormones, pubertal timing, sex, environmental factors, and more. The studies we typically do – although we work very hard to have robust sized samples – aren’t usually large enough to tease apart these potential drivers of neurodevelopment. I’m extremely excited for my lab to be contributing to these efforts.
CNS: What are you most looking forward to about CNS 2017 in San Francisco?
Somerville: I am most looking forward to having the opportunity to feature the work of my trainees, and to acknowledge the many mentors, collaborators, and students who have contributed to the work I’ll present.
-Lisa M.P. Munoz