7.3: The Brain and Cognition during Adolescence

During adolescence more complex thinking abilities emerge. Earlier researchers suggested this is due to increases in processing speed and efficiency rather than as the result of an increase in mental capacity—in other words, due to improvements in existing skills rather than development of new ones (Bjorkland, 1987; Case, 1985). However there has been a lot of research dedicated to studying adolescence and emerging adulthood. For example there is the Fundamentals of the Adolescent Brain Laboratory (FABLAB) at Yale University, the Developmental Social Neuroscience Lab at Univ of North Carolina, UCLA Center for the Developing Adolescent, and Society Youth Neuroscience Connected (SYNC lab) at Erasmus University in the Netherlands. (Casey, Getz & Galvan, 2008)

The brain undergoes dramatic changes during adolescence. Although it does not get larger, it matures by becoming more interconnected and specialized (Giedd, 2015). The myelination and development of connections between neurons continues. This results in an increase in the white matter of the brain, and allows the adolescent to make significant improvements in their thinking and processing skills. Different brain areas become myelinated at different times. For example, the brain’s language areas undergo myelination during the first 13 years. Completed insulation of the axons consolidates these language skills, but makes it more difficult to learn a second language. With greater myelination, however, comes diminished plasticity as a myelin coating inhibits the growth of new connections (Dobbs, 2012).

Even as the connections between neurons are strengthened, synaptic pruning occurs more than during childhood as the brain adapts to changes in the environment. This synaptic pruning causes the gray matter of the brain, or the cortex, to become thinner but more efficient (Dobbs, 2012). The corpus callosum, which connects the two hemispheres, continues to thicken allowing for stronger connections between brain areas. Additionally, the hippocampus becomes more strongly connected to the frontal lobes, allowing for greater integration of memory and experiences into our decision making.

The limbic system, which regulates emotion and reward, is linked to the hormonal changes that occur at puberty. The limbic system is also related to novelty seeking and a shift toward interacting with peers. In contrast, the prefrontal cortex which is involved in the control of impulses, organization, planning, and making good decisions, does not fully develop until the mid-20s.

Figure \(\PageIndex{1}\): In this sagittal section one can see the the subcortical regions of the brain like the amygdala and thalamus are responsible for emotions while prefrontal cortex (the front part of the outer covering) develops last and is responsible for inhibiting impulsive behavior. The locations of the brainstem, cerebellum and basal ganglia can be seen.

According to Giedd (2015) the significant aspect of the later developing prefrontal cortex and early development of the limbic system is the “mismatch” in timing between the two. The approximately ten years that separates the development of these two brain areas can result in risky behavior, poor decision making, and weak emotional control for the adolescent. When puberty begins earlier, this mismatch extends even further.

Teens often take more risks than adults and according to research, it is because they weigh risks and rewards differently than adults do (Dobbs, 2012). For adolescents, the brain’s sensitivity to the neurotransmitter dopamine peaks, and dopamine is involved in reward circuits so the possible rewards outweigh the risks. Adolescents respond especially strongly to social rewards during activities, and they prefer the company of others their same age. In addition to dopamine, the adolescent brain is affected by oxytocin which facilitates bonding and makes social connections more rewarding. With both dopamine and oxytocin engaged, it is no wonder that adolescents seek peers and excitement in their lives that could end up actually harming them.

Because of all the changes that occur in the adolescent brain, the chances for abnormal development can occur, including mental illness. In fact, 50% of the mental illness occurs by the age 14 and 75% occurs by age 24 (Giedd, 2015). Additionally, during this period of development the adolescent brain is especially vulnerable to damage from drug exposure. For example, repeated exposure to marijuana can affect cellular activity in the endocannabinoid system. Consequently, adolescents are more sensitive to the effects of repeated marijuana exposure (Weir, 2015).

However, researchers have also focused on the highly adaptive qualities of the adolescent brain which allow the adolescent to move away from the family towards the outside world (Giedd, 2015; Dobbs, 2012). Novelty seeking and risk-taking can generate positive outcomes including meeting new people and seeking out new situations. Separating from the family and moving into new relationships and different experiences are actually quite adaptive for society.

Prosocial behavior and complexity

For example, much research points out that the adolescent brain becomes more sensitive to social processing. Karan et al (2022) used fMRI analyses with charitable giving paradigms to provide further evidence for increased differentiation in prosocial behavior across the teenage years by which older adolescents increasingly give more to known others as compared to strangers. This differentiation in behavior was associated with age-related increases in brain activation in the lateral prefrontal cortex, suggesting an important role played by cognitive control networks in the developmental changes in prosocial behavior during the adolescent years. The significant patterns of activation in brain regions associated with cognitive control, social cognition, and reward processing highlight the important role played by developments in these networks for prosocial behavior during adolescence. Neural activation when giving to others increased with age in regions associated with cognitive control.

Greater stress and emotional wellness vulnerability

Zou et al’s (2022) study in China with more than 2000 11-17 year olds showed that high optimism is correlated with a subjective sense of wellbeing more than the absence of pessimism is. The latter is correlated more with depression. And these connections are mediated by positive reappraisal and acceptance.

References:

Casey, B. J., Getz, S., & Galvan, A. (2008). The adolescent brain. Developmental review : DR, 28(1), 62–77. https://doi.org/10.1016/j.dr.2007.08.003 (open access)

Dobbs, (2012). Beautiful brains. National Geographic, 220(4), 36.

Giedd, N. (2015). The amazing teen brain. Scientific American, 312(6), 32-37.

Karan, M., Lazar, L., Leschak, C. J., Galván, A., Eisenberger, N. I., Uy, J.P., Dieffenbach, M.C., Crone, E. A., Telzer, E.H., & Fuligni, A.J. (2022). Giving to others and neural processing during adolescence. Developmental Cognitive Neuroscience,
56, 101128. https://doi.org/10.1016/j.dcn.2022.101128 (open access)

Weir, (2015). Marijuana and the developing brain. Monitor on Psychology, 46(10), 49-52.

Zou, R., Hong, X., Wei, G., Xu, X., & Yuan, J. (2022). Differential effects of optimism and pessimism on adolescents’ subjective well-being: mediating roles of reappraisal and acceptance. International Journal of Environmental Research and Public Health, 19(12), 7067.

Attributions:

Child Growth and Development by Jennifer Paris, Antoinette Ricardo, and Dawn Rymond, 2019, is licensed under CC BY 4.0 (changes by Bhadha, 2023)

Parenting and Family Diversity Issues by Diana Lang, 2020, published by Iowa State University is licensed under CC BY-NC-SA 4.0