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(0) Comments. | Tags: adolescence, Barbara Ganzel, neurology, translational neuroscience, Evidence-Based Living
Reflection on our own adolescent years may include memories of excitingly risky activities or profound
emotional vulnerability, or both. Risk and vulnerability are at the heart of two critical themes in research on
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adolescence. Adolescence is a period of heightened risk-taking behavior (Steinberg, 2008) and it is also the peak
developmental period for the onset of psychological disturbance (Paus, Keshavan, & Giedd, 2008). However, a
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third theme in research on adolescence is at odds with these stereotypes of teenage emotional chaos and out-of-
Translational Neuroscience
control behavior. This third theme highlights youth resilience and the ability to adapt and thrive in the
expanding social world of the teenager (Crone & Dahl, 2012). Neuroscience unites these three themes by
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shedding light on the peculiarities of the adolescent brain and their impact on behavior. To understand
adolescent behavior, it is helpful to look at what is happening in the adolescent brain – and this is a story that
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In the developing human brain, there is a massive early
overgrowth in the number of connections or synapses
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between neurons (thus allowing a high degree of
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overabundance of synapses is countered by two major
malleability in the brains of the very young). This early
bouts of synaptic pruning, the first of which occurs in early
childhood (around age three) and the second of which
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occurs during adolescence. Pruning drives a 50 to 55%
decrease in the number of synapses across the entire cortex
between late childhood and early adulthood. This cortical
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thinning is a marker of brain maturation and is associated
with more adult-like cognitive abilities.
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Illustration of synapses. credit: Wellcome Images
During pruning, any neural connections that have not been
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consistently used are eliminated. Thus, when we were adolescents, pruning served to streamline the efficiency
of networks of neurons that we used most often. Our brains were sculpted to fit our own particular environment
(a real life example of “you are what you do”). At the same time, increasing thickness and density of fatty white
matter (myelin) served to insulate the “wiring” between neurons. This effectively boosted transmission power
across the long connections in the brain that underlie the extended neural networks responsible for complex
thought and behavior. Thus, during adolescence and young adulthood, pruning and myelination worked
together to establish and strengthen the higher-order neural networks that we use for planning and regulating
what we do.
Different brain areas develop at different rates and the prefrontal cortex
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(PFC) is among the last brain regions to mature. This is not surprising,
since it is the most interconnected area of the brain. The PFC is referred
http://www.bctr.cornell.edu/life-and-the-adolescent-brain/[5/8/2013 10:46:47 AM]
Life and the Adolescent Brain | Bronfenbrenner Center for Translational Research | BCTR
to as the ‘C.E.O’ of the brain since it is involved in executive functioning.
These executive functions include planning, decision making, and
direction of working memory, i.e., the ongoing thought processes that
allow us to complete tasks and plan for the future. The PFC is capable of
promoting such complex human thought because of its connections with
other members of the brain community. Within the adolescent PFC,
pruning and myelination are creating big improvements in the finetuning of local connections, as well as profoundly strengthening its longdistance communications with the rest of the brain. These long-distance
connections form the integrative neural networks responsible for higher
level processing such as self-perception and goal-directed behavior, and
credit: Ryan Mercer
so they are crucial to making rational decisions and regulating
emotional drives. These “smart circuits” finish their development last
because they are continuously refined and polished across adolescence and young adulthood. This is a big factor
in the unique way that adolescents process their experiences and navigate their environment.
First, there may be a lag in the connections between the
PFC and those regions of the brain devoted to motivated,
reward-seeking behavior. A substance in the brain called
dopamine is the primary chemical signaler in this network.
During adolescence, there are excessive levels of dopamine
in these regions, leading to increased activation of these
reward systems. In turn, adolescents demonstrate elevated
exploration and reward-seeking behavior. There is
neuroimaging evidence that the adolescent PFC is not yet
able to effectively inhibit this increased reward-seeking.
These ‘rewards’ that an adolescent is after could be
anything from drugs and alcohol to social acceptance. In
credit: Jeremy Eades
the pursuit of the positive feelings driven by this circuitry,
teens may drink, do drugs, or have unprotected sex.
The PFC has strong connections to brain regions that underlie emotion processing. These are areas of the brain
that direct our survival-related behaviors (sometimes called “the four F’s” – feeding, fight, flight, and sex). These
circuits also underlie the formation of social bonds, which have been key in our evolutionary history of
overcoming hardships through group cooperation. These brain regions initiate pleasant emotional states of
desire, as well as negative feelings when we feel fearful, ashamed, or rejected. When these ‘higher order’ social
networks include a mature PFC, they allow us to behave effectively in social situations. The PFC guides our
attempts to impress and comfort others, to empathize, and to having deeply meaningful exchanges with our
fellow man about what we experience.
Neuroimaging technology allows scientists to measure activity within the neural circuits that underlie these
behaviors. In one study, adolescents saw pictures of emotional images, such as the disapproving or angry face of
a peer, while their brains were being imaged in a magnetic resonance imaging (MRI) scanner. Those adolescents
who were less resistant to peer pressure showed evidence of weak connections between their prefrontal cortex
and their reward areas, and those who were more socially resistant showed stronger, more mature connections
between these areas. The authors of the study concluded that socially resistant adolescents were better able to
recruit their PFC to help them regulate their emotions when faced with negative social information. It was
suggested that this, in turn, may allow these young people to resist social pressure to engage in risky behavior
(Grosbras et al., 2007).
Adolescents are more attuned to how others respond to
them, picking up on subtleties of social exchanges and
attributing meaning to them. They tend to be highly
sociable and sensitive to acceptance and rejection from
peers -- more so than children or adults. This social
intensity may be due, in part, to higher adolescent levels of
another chemical signaler, oxytocin, a hormone that
enhances social emotions in mammals. A mature PFC is
http://www.bctr.cornell.edu/life-and-the-adolescent-brain/[5/8/2013 10:46:47 AM]
Life and the Adolescent Brain | Bronfenbrenner Center for Translational Research | BCTR
more able to modulate social highs and lows associated
with social acceptance and social rejection. The stillcredit: Joseph Vasquez
developing adolescent PFC is less able to do so, so that a
social threat is more likely to initiate the neural and
hormonal cascades and negative feelings that we
experience as stress. For example, an adolescent girl may angst over the details of exchanges with boys. Another
teen’s self-esteem may be decimated by being picked last in gym class. Happily, this increased sensitivity to the
social world may also allow social support to have an elevated beneficial effect for teens experiencing stress. For
example, research on social buffering investigates how the presence of supporting and comforting others can
help to decrease the intensity of the stress response and its associated negative feelings. These studies find that
social buffering effects are amplified during adolescence, so that teens more readily absorb the positive effects
of social support in the face of stress (Buwalda, Geerdink, Vidal, & Koolhaas, 2011). This finding suggests that
interventions that enhance healthy social buffering may be particularly helpful for our stressed teens.
Adolescent brain development provides some insight into why adolescents take more risks, have increased odds
of experiencing psychological distress, and rely heavily on peer approval. It has been argued, though, that study
of the adolescent brain has done more to reveal that this developmental period is ripe with opportunity.
Although the adolescent PFC is less efficient in inhibiting emotionally-driven impulses, a new line of research
suggests that this very lack of maturity allows greater cognitive and social flexibility (Crone & Dahl, 2012). Not
only is the adolescent brain is still changing and adapting to environments, it is able to more quickly switch
attention to novel social features of the environment. This gives adolescents an advantage in navigating their
complex social worlds, and in creatively pursuing new friendships and connections. Thus, neuroscience tells us
that the adolescent brain is not merely immature, but rather it is perfectly suited to foster exploration of new
environments, soak up the benefits of social closeness, and mold future adult capabilities.
Dr. Barbara Ganzel, Director, Laboratory for Lifespan Affective Neuroscience
[email protected]
Sarah Moore, graduate student, Human Development
References
Buwalda, B., Geerdink, M., Vidal, J., & Koolhaas, J.M. (2011). Social behavior and social stress in adolescence.
Neuroscience & Biobehavioral Reviews, 35(8), 1713-1721.
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.
Grosbras, M., Jansen, M., Leonard, G., McIntosh, A., Osswald, K., Poulsen, C., & Paus, T. (2007). Neural
mechanisms of resistance to peer influence in early adolescence. The Journal of Neuroscience, 27(30), 80408045.
Paus, T., Keshavan, M., & Giedd, J. N. (2008). Why do many psychiatric disorders emerge during adolescence?
Nature Reviews Neuroscience, 9(12), 947-957.
http://www.bctr.cornell.edu/life-and-the-adolescent-brain/[5/8/2013 10:46:47 AM]
Life and the Adolescent Brain | Bronfenbrenner Center for Translational Research | BCTR
Steinberg, L. (2008). A social neuroscience perspective on adolescent risk-taking. Developmental Review, 28(1),
78-106.
BCTR Resources on adolescent neurology
Video of talks on the adolescent brain from the 2011 Bronfenbrenner Conference, The Neuroscience of Risky
Decision Making, are available here. They include:
Eveline Crone, Adolescent Brain Development: A Window of Opportunity for Learning and Social
Cognition
Jay Giedd, The Adolescent Brain: New Views from Neuroimaging
Beatriz Luna, Adolescent Risk Taking: Immaturities in Cognitive Control and Reward Processing
Also see the recent book The Adolescent Brain co-edited by BCTR faculty affiliate Valerie Reyna and published
by the American Psychological Association.
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