QnAs with Leah H. Somerville

Adolescence is a period of significant change during human development. During this period, the brain undergoes developmental changes that are often reflected in psychological and behavioral changes. Leah H. Somerville studies the interplay between brain and psychological development from childhood to adulthood. Somerville, a professor of psychology at Harvard University, is also a principal investigator on the Human Connectome Project in Development, an effort funded by the NIH to map the evolution of connections in the brain throughout development. In recognition of her achievements as an early-career researcher in the field of experimental psychology, Somerville was a recipient of the 2022 Troland Research Award (1). Somerville spoke with PNAS about her interdisciplinary approach to exploring how brain and psychological development are intertwined during human adolescence.

Leah H. Somerville. Image credit: Anna Olivella (photographer) and the Harvard Brain Science Initiative.

PNAS: How did you become interested in the intersection of brain and psychological development during adolescence?

Somerville: I’ve always been interested in human development and the potential for people to change over their lifetimes. When I was in college, I started volunteering at a crisis shelter for youth who are homeless or runaways, and that really stamped in a lot of interest about why this time of life is one that has such immense potential for both positive and negative trajectories to present themselves. I’ve been interested all the way since then about what might contribute to people progressing along a more positive or negative trajectory during this part of life.

PNAS: Much of your work takes an interdisciplinary approach, incorporating cognitive, social, and affective neuroscience, as well as clinical and decision science. What are the advantages of this approach?

Somerville: The most interesting questions to me [have] to do with how brain development shapes the way that we think, feel, make decisions, and function in daily life. Understanding what brain development looks like from a purely neuroscientific angle is really important but, as a psychologist at heart, the things that get me the most excited have to do with the linkages between brain development and some kind of consequence or outcome for a person’s behavior and functioning. That’s a naturally interdisciplinary space. Pursuing those kinds of questions requires an interdisciplinary perspective that’s considering both the measurement and characterization of brain development on one hand, and then also incorporating within those measures experimental tasks or other measures that will tell us something about a person’s functioning. These can be done simultaneously using functional brain imaging, where people would complete a psychologically minded experimental task at the same time as brain activity is being measured.

PNAS: What is an example of a typical milestone in adolescent brain development that is reflected in behavior and psychology?

Somerville: One example is in the domain of thinking about goal-directed behavior: the capacity to orchestrate our behavior in the moment according to a set of goals or rules imposed by the environment to make the right moves at the right times to maximize getting what we want. And that’s a broad umbrella topic. We’ve looked at topics like how value cues might shape goal-directed behavior. We can apply strategies as adults, for example, amping up performance when it really counts and slacking off performance when it counts less, in order to preserve … effort that we find costly. And one of the things we’ve found is that this capacity to take goal-directed objectives or plans for ourselves in our environments and implement them in the moment is something that seems to be getting better and better and refining itself as we develop through adolescence. That means adolescents can do many of the same tasks and even very challenging cognitive tasks, like adults can, but the tuning of effort and performance according to the bigger goals is something that they seem to be continuing to develop. We found that certain aspects of brain connectivity development mediate those performance gains so that, as we’re growing up and becoming more goal-directed in our daily actions, that seems to be supported by emerging [increases] in brain connectivity that are facilitating that performance. So that’s just one example that links behavior, its development, and brain development.

PNAS: What are some of the developmental health concerns common to adolescence?

Somerville: Adolescence is a time [when] brain development is continuing to unfold based on experience. It’s also a time [when] puberty hormones are remodeling the brain and body in a very active way. And so there are multiple, different co-occurring changes that could shape things like well-being and daily functioning. At the psychological level, adolescence is the most common period of life for first onset of mental illnesses. Most major mental illnesses emerge during adolescence, with an age of about 14 as the most common age of a first expression of mental illness. So what is it about this time of life that leads to this risk profile for mental health problems? It could be merely that this is a stressful period of life where there’s lots of changes, but it could also involve the unique biological and psychological state of this period of life as well. Unraveling what these contributions are is of really central interest to many researchers, including us.

PNAS: What potential opportunities do you see for the Human Connectome Project in Development to inform other areas of your work?

Somerville: One of the directions we’re taking is to try to understand the role of hormonal changes of puberty in shaping brain development and then, ultimately, psychological functioning in a number of domains. We know that the hormonal changes of puberty influence the brain from previous research. But how exactly, and when exactly, and for whom, and what that link looks like, remain fuzzy. To do this work, we need to have these large and diverse datasets that measure puberty in multiple different ways. And so we see a lot of opportunity here to try and unpack what about brain development specifically and what drivers of brain development may be shaping psychological functioning in … domains…, like goal-directed actions and social behavior. So, we’ve built in substudies within the Connectome Project to try and reveal that, and we’re bringing in additional measures of pubertal hormones that we hope will help us characterize what about the brain is changing, which I think will help us take a more mechanistic look at what brain development is all about.