Developing the Social Brain: Insights from the Science of Adolescence

Adolescence is the period between childhood and adulthood that largely coincides with the years of secondary schooling. This stage of life is characterized by many cognitive changes. One such change is in social signal sensitivity. Recent research has provided evidence for adolescence as a time of heightened receptivity and sensitivity to complex social signals in the environment, which are reflected in typical brain development patterns¹.

Developmental tasks

We are faced with certain developmental tasks at different points in our life. This means that we are expected to acquire certain skills or abilities at certain developmental stages. For instance, infants and young children are tasked to develop certain sensory and motor skills. And the human brain at this period of life reflects this, as it produces an excess number of connections between brain cells (called synapses) in sensory and motor cortices in early infancy, which are then pruned (or lost over time) to their adult levels across the first decade of life.

When it comes to the connections in the brain, more does not always mean better.

In fact, ‘synaptic pruning’ often allows the brain to communicate more efficiently.

The human brain also overproduces synapses in other regions of the cortex during infancy, such as the prefrontal cortex. However, unlike the sensory and motor cortices, the connections formed in this part of the brain continue to be pruned across the teenage years and into the twenties^2,3.

This prolonged development of the prefrontal cortex has intrigued developmental neuroscientists for decades. Given that synaptic pruning coincides with an increase in abilities associated with a given cortical area, perhaps the prolonged synaptic pruning of the prefrontal cortex coincides with the increased abilities associated with this part of the brain? This question underlies many developmental neuroscience studies.

In flux: The prefrontal cortex

The prefrontal cortex is often discussed as the hallmark of human cognition. Many complex cognitive abilities, such as inhibiting inappropriate behavior, planning for the future, and inferring the mental states of others, require the prefrontal cortex. It might be intuitive to many educators that an area of the brain involved in these complex behaviors and abilities is still developing throughout the teenage years.

However, the prefrontal cortex is not the neurological root of all behavioral changes between adolescence and adulthood.

The brain operates on a network level, which means that many different brain regions are constantly communicating with each other. While each region might have its own specific role, it is how the networks interact that ultimately matters. You can think of it as kind of like a team. Each member has its own role to play—and if a member gets weaker or stronger then it can change the way the team works—but the end result is a product of the whole team working together.

In flux: The nucleus accumbens

While the prefrontal cortex is often lauded as the seat of rational behavior, the nucleus accumbens is often demeaned as the cause of human hedonism or impulse. This subcortical brain region, hidden deep within the brain, is best known for its involvement in reward processing. Early research in rodents found evidence for dramatic remodeling of dopamine receptors in the nucleus accumbens during puberty⁴. This means that there was a change in how cells process dopamine, which is a neurotransmitter often connected to the experience of pleasure or rewards. Early fMRI studies then found increased recruitment of the nucleus accumbens in adolescence during reward processing⁵. This finding prompted developmental scientists to hypothesize that adolescent behaviors might be more influenced by nucleus accumbens signaling (or the sensitivity of this area to neurotransmitters like dopamine), which could explain why adolescents are drawn to risky or rewarding behaviors⁶. This heralded a change in thinking in developmental neuroscience. Rather than simply attributing adolescent changes to the developing prefrontal cortex, this new model posited that the changing interactions between the prefrontal cortex and nucleus accumbens underlie behavioral differences between adolescence and adulthood.

Not so simple

The model that I just described is more complex than can be described in a short blog post (see Further Reading). However, at its core is the interplay between two systems: one involved in socio-emotional processing and the other in cognitive control⁶. Subcortical regions such as the nucleus accumbens are considered part of the socio-emotional processing system because they are recruited during rewarding social interactions or emotional scenarios. However, we know that cortical regions are also involved in social cognitive processing (see previous blog post), and therefore these systems are starting to be taken into account when considering the neural correlates of adolescent behavior^7,8.

Social brain development

The network of brain regions involved in understanding or inferring the mental states of others (i.e. mentalizing) continues to develop across adolescence. Although they aren’t exclusively involved in mentalizing, these regions—the dorsomedial prefrontal cortex, temporal parietal junction, posterior superior temporal sulcus and anterior temporal cortex—are consistently recruited when individuals perform tasks that require understanding or inferring the mental states of others. Longitudinal studies of brain structure have found that these regions undergo substantial changes in structure throughout adolescence⁹.

And as described in my previous post, adolescents utilize the medial prefrontal cortex more than adults in tasks that require understanding the mental states of others¹⁰. Taken together, these changes in structure and function provide evidence for the continued development of a brain network involved in complex socio-cognitive processes that influence how we navigate the social world.

The developmental tasks of adolescence

Now, why would we expect adolescence to be a sensitive period for social brain development? The period of adolescence, which can be defined as beginning around puberty, is typically considered finished when one has reached a relatively stable role in society. Therefore, one of the major developmental tasks of adolescence is to learn how to navigate the complex social world of one’s society. Adolescents are more equipped to do this than children because they have the necessary cognitive abilities as well as the motivational drive to learn from their social environment. Educators can build on these capacities in learning settings if social motivation is used to bolster learning rather than seen as another behavior to inhibit in the classroom.

An aside on the nucleus accumbens and risk-taking

Earlier I described the nucleus accumbens being involved in reward processing. While this is true, it is also true that the nucleus accumbens is involved in learning. In a way, we can think of the nucleus accumbens as a sort of salience detector—it helps us know what to pay attention to in the environment. Therefore, the heightened sensitivity of the nucleus accumbens in adolescence presents a great opportunity for learning. Further, risk-taking is not inherently a bad behavior. In fact, we need to take many risks in order to succeed in the modern educational environment.

Encouraging these educational risks, which can be as minor as raising one’s hand to answer a question in front of one’s peers, or as substantial as spending the time to learn a new programming language, might be one way to take advantage of the natural inclinations of being young and flexible.

References

1. Blakemore, S.-J., & Mills, K. L. (2014). Is Adolescence a Sensitive Period for Sociocultural Processing? Annual Review of Psychology, 65(1), 187–207. [Paper]
2. Huttenlocher, P. R. (1979). Synaptic density in human frontal cortex — Developmental changes and effects of aging. Brain Research, 163(2), 195–205. [Paper]
3. Petanjek, Z., Judaš, M., Šimic, G., Rasin, M. R., Uylings, H. B. M., Rakic, P., & Kostovic, I. (2011). Extraordinary neoteny of synaptic spines in the human prefrontal cortex. Proceedings of the National Academy of Sciences of the United States of America, 108(32), 13281–13286. [Paper]
4. Andersen, S. L., Rutstein, M., Benzo, J. M., Hostetter, J. C., & Teicher, M. H. (1997). Sex differences in dopamine receptor overproduction and elimination. Neuroreport, 8(6), 1495–1498. [Paper].
5. Galvan, A., Hare, T. A., Parra, C. E., Penn, J., Voss, H., Glover, G., & Casey, B. J. (2006). Earlier Development of the Accumbens Relative to Orbitofrontal Cortex Might Underlie Risk-Taking Behavior in Adolescents. The Journal of Neuroscience, 26(25), 6885–6892. [Paper]
6. Steinberg, L. (2008). A Social Neuroscience Perspective on Adolescent Risk-Taking. Developmental Review: DR, 28(1), 78–106. [Paper]
7. Crone, E. A., & Dahl, R. E. (2012). Understanding adolescence as a period of social-affective engagement and goal flexibility. Nature Reviews. Neuroscience, 13(9), 636–650. [Paper]
8. Pfeifer, J. H., & Allen, N. B. (2012). Arrested development? Reconsidering dual-systems models of brain function in adolescence and disorders. Trends in Cognitive Sciences, 16(6), 322–329. [Paper]
9. Mills, K. L., Lalonde, F., Clasen, L. S., Giedd, J. N., & Blakemore, S. J. (2014). Developmental changes in the structure of the social brain in late childhood and adolescence. Social Cognitive and Affective Neuroscience, 9(1), 123–131. [Paper]
10. Blakemore, S.-J. (2008). The social brain in adolescence. Nature Reviews. Neuroscience, 9(4), 267–277. [Paper]

Further Reading

• Casey, B. J., Getz, S., & Galvan, A. (2008). The adolescent brain. Developmental Review: DR, 28(1), 62–77. http://doi.org/10.1016/j.dr.2007.08.003
• Gardner, M., & Steinberg, L. (2005). Peer influence on risk taking, risk preference, and risky decision making in adolescence and adulthood: an experimental study. Developmental Psychology, 41(4), 625–635. http://doi.org/10.1037/0012-1649.41.4.625
• Mills, K. L., Goddings, A.-L., Clasen, L. S., Giedd, J. N., & Blakemore, S.-J. (2014). The developmental mismatch in structural brain maturation during adolescence. Developmental Neuroscience. http://doi.org/10.1159/000362328
• Somerville, L. H., & Casey, B. J. (2010). Developmental neurobiology of cognitive control and motivational systems. Current Opinion in Neurobiology, 20(2), 236–241. http://doi.org/10.1016/j.conb.2010.01.006
• Somerville, L. H., van den Bulk, B. G., & Skwara, A. C. (2014). Response to: The triadic model perspective for the study of adolescent motivated behavior. Brain and Cognition. http://doi.org/10.1016/j.bandc.2014.01.003
• Steinberg, L. (2010). A dual systems model of adolescent risk-taking. Developmental Psychobiology, 52(3), 216–224. http://doi.org/10.1002/dev.20445