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The period of adolescence involves changes in almost every brain structure (Luciana 2010). Numerous studies have been able to identify how these changes link to cognitive, behavioral, and emotional changes (see Steinberg 2008). Although reviews and analyses tend to weave narratives that show consistent findings, some studies continue to offer mixed and contradictory results that challenge efforts to discern what neural and other changes cause particular cognitive, behavioral, and emotional changes (Spear 2000; Luciana 2010). This essay summarizes important emerging findings in this area of research as it underscores that this highly active area of research continues to present new findings that push the field in many different and innovative directions that often challenge earlier findings and offer new understandings of previously unknown phenomena. The essay ends by noting some key areas for future research.
Researchers have reported that while there seems to be large amounts of growth in childhood and subsequent synaptic pruning in gray matter during adolescence (Giedd et al. 1999), cognitive maturity increases during adolescence (Spear 2000). This pruning is especially seen in the cortex (Sowell et al. 1999), the frontal lobes (Giedd et al. 1999), and parietal lobes (Giedd et al. 1999). Instead of causing malfunction, pruning serves to refine connections that are overproduced (Purves 1998; Whitford et al. 2007). In their impressive review, Gogtay et al. (2004) report, for example, how gray matter develops in what appears to be an evolutionary-based sequence, namely, the sensorimotor cortex, frontal, and occipital lobes developing first, followed by a back-to-front maturation in the cortex. Finally, the superior temporal cortex develops an area that integrates object- and space-related information (Karnath 2001).
White matter, especially in the frontal lobe and hippocampus, also increases (Benes 1989; Benes et al. 1994), a development thought to reflect an increase in myelination (Paus et al. 2001). Paus et al. (2001) also documented an increase in myelination in a segment of the brain that connects Broca’s and Wernicke’s areas. These together have been associated with an increase in language and memory abilities in adolescence (Nagy et al. 2005; Paus et al. 2001). In addition, researchers also have noted an increase in myelination in the prefrontal cortex, a development thought to be associated with increased cognitive functioning (Paus et al. 1999). This process is similar to synaptic pruning, where highly used pathways become myelinated (Bengtsson et al. 2005).
As the brain matures, that maturity links to adolescents’ ability to engage in increasingly complex cognitive and emotional processes important for managing more effective social relationships. Maturation in the superior temporal sulcus may be seen, an area that influences the processing needed for various body movements (Paus 2005). Findings of fMRI studies corroborate electrophysiological evidence of maturation of nonverbal processing circuitry, which follows closely with the increase seen in an adolescent’s ability to process social cues (Paus 2005). For example, an increase in activity in the amygdala is seen in adolescence (Baird et al. 1999), which is responsible for the processing of emotions. Change in the prefrontal cortex also has been noted. Casey et al. (1997) demonstrated a refinement in functioning between children and adults in the dorsolateral prefrontal cortex, which is associated with planning and impulse control, while Galvan et al. (2006) demonstrated low activity in the orbital-frontal cortex, which is implicated in impulsivity (Galvan et al. 2006) and reward evaluation (Steinberg 2008). Functional maturity has been seen in the ventromedial prefrontal cortex (Hooper et al. 2004), which is responsible for decision-making and connected to the emotional center of the brain, the limbic system (Steinberg 2008).
Along with the amygdala, other changes in the limbic system occur, including myelination in the hippocampus (Benes 1989). Increases in levels of neurotransmitters in the limbic system are thought to influence social information processing, supporting the increase in peer interest during adolescence (Steinberg 2008). Researchers suggest that, because the limbic system matures quicker than the prefrontal cortex, adolescence is a time of increased risk-taking and behavioral problems (Steinberg 2008). Although it is important not to link certain brain developments to specific outcomes, it certainly does appear that brain maturation can play an important role in increasing certain vulnerabilities. And, of course, that vulnerability also means that the adolescent brain does have a high level of plasticity that makes this period a time of considerable opportunity for intervention.
Hormones are thought to play an integral role in adolescent brain development, although not much is known about the connection between behavior and pubertal changes (Luciana 2010). Dopamanergic systems undergo a significant increase in developmental changes, including the prefrontal cortex, striatum, and nucleus accumbens (Spear 2009). GABAergic circuits in the prefrontal cortex also appear to decrease during adolescence (Spear 2000). Some studies also indicate that changes in dopamine system activity may account for adolescents’ increases in reward seeking behavior (Luciana 2010). The strongest evidence examining the effects of hormonal changes emerges from research examining how pubertal changes influence behavior or vice versa. That research suggests that hormonal changes at puberty activate specific motivational tendencies that lead adolescents to pursue social experiences, such as increases in sensation-seeking as well as social reorientation toward peers (for a review, see Forbes and Dahl 2010). This line of research highlights how pubertal development may be central to understanding emotional and social development during adolescence.
Two other areas of research relating to brain maturation are important to highlight. The first involves reports that a number of sex differences characterize structural brain development during adolescence (for a review, see Lenroot and Giedd 2010). That research reveals, for example, that gray matter volumes peak earlier in males in the frontal, temporal, and parietal regions; it also reveals sexual dimorphism in white matter development, with males showing steeper increases in white matter volume across adolescence. The second key point relating to brain maturation and adolescent development is the well-established finding that adolescence is clearly a risk period for the emergence of clinical disorders (Paus et al. 2008). The risk for disorders may not be equivalent for all individuals, but links exist between brain development and schizophrenia, substance abuse, and affective pathology (see Gogtay and Thompson 2010). Importantly, the risks relate closely to sex differences as well, as shown in research on the rates and developmental peaks of depression and schizophrenia (see Lenroot and Giedd 2010).
No doubt exists that the brain matures quickly during the adolescent period, but how that development influences other aspects of development remains a challenging area to research. Much research has sought to identify specific links between parts of the brain and social, cognitive, or emotional outcomes. Research does show that the entire brain is maturing during adolescence as functional networks become more efficient in the processing of information, among other critical changes. The recent trend in research, however, increasingly focuses on viewing the widespread changes characteristic of adolescents’ brain organization in a more integrative fashion. As a result, research now aims to examine how structural changes relate more closely to functional changes and behaviors. Other important research seeks to understand the importance of hormonal changes’ interactions with structural brain changes and subsequent behavior. Still other areas focus on the importance of social contexts, as highlighted by research on social cognition and vulnerability to psychopathology. These avenues of research are but a few examples of efforts to understand how, and to what effect, dramatic changes in brain maturation occur during the period of adolescence.
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Levesque, R.J.R. (2011). Brain Maturation. In: Levesque, R.J.R. (eds) Encyclopedia of Adolescence. Springer, New York, NY. https://doi.org/10.1007/978-1-4419-1695-2_16
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