In psychological research, we tend to assume that people fall into just a few developmental groups: children (before puberty), adolescents (going through puberty), and adults (after puberty). However, if you were to approach the average college freshman and ask her if she felt like she behaved and thought like the average 40-year-old woman, she would probably say no. This idea of continued development after adolescence isn’t a particularly new one, having been described for decades now by various researchers in psychology, but it wasn’t until the year 2000 that Jeffrey Arnett, a researcher at the University of Maryland, proposed that it be recognized as a distinct period of development known as emerging (or early) adulthood (EA; Arnett 2000).
EA is a time period in an individual’s life that is characterized by both external and internal changes. Externally, secondary schooling ends at age 18, and graduates make the decision whether they want to continue into postsecondary education, join the workforce, or do something else entirely. Environments change, often multiple times, as these early adults move out of their parents’ homes and into dorms, apartments, or other living situations with friends, significant others, spouses, or strangers. Once high school is finished, the world opens up to seemingly endless possibilities of what one could do next. Any early adult is already aware of this phenomenon; a 20-year-old might have a friend in college, another who got married and had a baby right out of high school, and another who started their own company and is making a six-figure salary.
We often tend to think of things like self-exploration and identity formation in terms of adolescence, as teenagers begin to push away their parents and feel more influenced by their peers, but college is famous for being a coming-of-age sort of environment. Early adults in college start to associate more with peers that are like-minded and discover, out of the confines of high school class requirements, what they truly enjoy studying. Those who join the workforce start to figure out what kind of work they want to do for the rest of their lives and who they want to associate with in their spare time. With all of these external changes, it’s no wonder that things internally haven’t finished developing yet. Yet research and society still have a strong tendency to associate anyone over the age of 18 with the idea of adulthood. In the United States, at the age of 18, you have a voice in choosing the leadership of the nation; you can decide to join the armed forces; you no longer have to share any academic or medical information with your parents (including decisions to engage in psychological research). For all intents and purposes, you are an adult. But we have learned, increasingly so over just the past couple of decades, that both behaviorally and neurologically, you might not quite be there yet.
Research on this stage of life is still in its early years, so we don’t know everything yet that there is to know about how EA is different than adolescence or later adulthood. Many studies, though, have shown us time and time again that there are developmental trajectories that continue past puberty and into legal adulthood. In terms of the brain, we know that white matter (the axons and myelin sheaths that physically connect brain regions and transmit messages from one part of the brain to another) does not stop developing until the twenties (Lebel et al. 2008), with some tracts (or pathways) not reaching peak maturity until as late as age 40 (Lebel et al. 2012). What this means is that even after leaving behind the life stage of adolescence, early adults’ brains are still working to optimize connectivity between different regions.
One white matter tract in particular that continues to develop post-adolescence is the uncinate fasciculus. This tract connects the limbic system, which is associated with functions like emotion and episodic memory, to the frontal lobe, which is one of the evolutionarily newest parts of the brain and is associated with higher-order functioning like reasoning, decision-making, and planning. The uncinate fasciculus is one of the later tracts to develop, and, while its exact function isn’t entirely known, its association with clinical disorders such as autism spectrum disorders and conduct disorder provide some evidence for its role in socio-emotional functioning (Olson et al. 2015).
Looking at gray matter in the brain tells a similar story; the total amount of gray matter continues to change even past adolescence, with some of the most noticeable and important differences occurring in the prefrontal cortex, which is part of the frontal lobe mentioned earlier. Vijayakumar and colleagues (2017) showed this in a task-based context. They looked at a number of previously completed studies (a method called a meta-analysis) to see what brain regions were most associated with a social exclusion task known as Cyberball in an early adult sample. In this meta-analysis, they found that the ventrolateral prefrontal cortex continued to show changes in how it responded to social exclusion after the end of adolescence (Vijayakumar et al. 2017). Studies like these provide us with a biological lens through which to view the changes still occurring in EA.
On the other hand, we can also see differences between early adults as compared to adolescents and later adults without looking at the brain itself. An area that has caught the attention of some EA researchers is that of risk-taking. Here, we again see this story of continued development in EA, where early adults engage with risk differently than adolescents, but have not yet reached the optimal level of risk taking that adults generally achieve (Brodbeck et al. 2013). Not only does this bring into focus how some of the continued brain development might play out in EA (the higher-level functions of prefrontal cortex are needed in order to inhibit risky behaviors), but it also shines a light on where these developmental processes can lead to psychological issues like addiction (Sussman and Arnett 2014).
In general, psychological research tends to focus on adolescence as a period of heightened vulnerability to mental disorders, and while this is true, the field is starting to recognize that EA is also an important period that exhibits sensitivity to the development of disorders like addiction, but also like depression and schizophrenia (Taber-Thomas and Perez-Edgar 2015). EA is a life stage associated with great external and internal change, and this kind of instability can render a person vulnerable to additional changes that could develop into a full-blown disorder. To give just one example, schizophrenia has been shown to be associated with less gray matter in parts of the prefrontal cortex (e.g. Hooker et al. 2011), a region that is already undergoing changes during EA (as discussed above).
With so many illnesses exhibiting an increased prevalence during this life stage, and so many changes in the brain and behavior occurring even in normal development after adolescence, studying EA provides us with a wealth of knowledge that will help us both to understand what is happening in the internal life of early adults and what it looks like when something abnormal is happening. Continued research on EA will lead us to a clearer understanding of why a college freshman and a 40-year-old woman don’t think the same way, a fact that is often overlooked in many contexts both within and outside of psychological research.
References
Arnett, J. J. (2000). Emerging adulthood: A theory of development from the late teens through the twenties. American psychologist, 55(5), 469.
Brodbeck, J., Bachmann, M. S., Croudace, T. J., & Brown, A. (2013). Comparing growth trajectories of risk behaviors from late adolescence through young adulthood: An accelerated design. Developmental psychology, 49(9), 1732.
Hooker, C. I., Bruce, L., Lincoln, S. H., Fisher, M., & Vinogradov, S. (2011). Theory of mind skills are related to gray matter volume in the ventromedial prefrontal cortex in schizophrenia. Biological psychiatry, 70(12), 1169-1178.
Lebel, C., Walker, L., Leemans, A., Phillips, L., & Beaulieu, C. (2008). Microstructural maturation of the human brain from childhood to adulthood. Neuroimage, 40(3), 1044-1055.
Lebel, C., Gee, M., Camicioli, R., Wieler, M., Martin, W., & Beaulieu, C. (2012). Diffusion tensor imaging of white matter tract evolution over the lifespan. Neuroimage, 60(1), 340-352.
Olson, I. R., Von Der Heide, R. J., Alm, K. H., & Vyas, G. (2015). Development of the uncinate fasciculus: implications for theory and developmental disorders. Developmental cognitive neuroscience, 14, 50-61.
Sussman, S., & Arnett, J. J. (2014). Emerging adulthood: developmental period facilitative of the addictions. Evaluation & the health professions, 37(2), 147-155.
Taber-Thomas, B., & Perez-Edgar, K. (2015). Emerging adulthood brain development. In The Oxford handbook of emerging adulthood (pp. 126-141). New York, NY: Oxford University Press.
Vijayakumar, N., Cheng, T. W., & Pfeifer, J. H. (2017). Neural correlates of social exclusion across ages: A coordinate-based meta-analysis of functional MRI studies. Neuroimage, 153, 359-368.