Inside the Adolescent Brain

IN A longitudinal study of 1,800 teenagers over 13 years at the American National Institute of Mental Health (NIMH), Dr Jay Giedd, has shown that the brain seems to go through a process of developmental restructuring that accounts for both the aberrations of adolescent behaviour and the gradual transition to adult maturity.

Adolescents apparently lose up to 15% of their grey matter, matched by a corresponding increase in white matter throughout this transition. This process of neural ‘waxing and waning’ alters the number of connections, or synapses, between neurons. Along with the remodeling of the brain is a wiring upgrade as axons (long nerve fibers that neurons use to send signals to others) become more insulated with myelin (fatty white matter), which eventually boosts the axon’s transmission speed by a 100 times.

This process of myelination is critical for learning. If myelination was completed in our teens, we would lose flexibility for all the nimble learning that needs to take place as we separate and individuate from our family.

This period of brain plasticity is also the best time for teenagers to cultivate skills in areas like languages, instruments, sports and the performing arts.

So, if a teen is engaged in music or sports or academics, those are the cells and connections that will be hardwired for preservation into adulthood. If they are vegetative on the couch playing games, those are also the cells and connections that are going to survive.

Evolution Of The Brain

Throughout the adolescent years this slow wave of brain reconfiguration is advancing – starting with the back of the brain and slowly working its way towards the front. Those cells and connections that are used survive and thrive, while those that are not, wither and die.

The final part of the brain to be pruned and shaped to its adult configuration is the pre-frontal cortex and this is home of the so-called executive functions — planning, setting priorities, organizing thoughts, suppressing impulses, weighing the consequences of one’s actions, or governing a tribe.

Much has been made of this discovery of delayed development of the pre-frontal cortex. The fact that the pre-frontal cortex is still growing and re-sculpting throughout the teenage years and into the mid-20s, essentially means that the adolescent brain is functioning without its executive “override”, that tiny voice of caution that keeps young people from reacting impulsively and becoming a statistic for the Darwinian award.

Natural selection swings a sharp edge, and the teen’s sloppier moments can bring unbearable and tragic consequences.

While the more rational pre-frontal cortex is taking its time to develop, adolescents might be relying on the limbic system, the emotional seat of the brain, to make decisions and solve problems, and this spells trouble.

Part of the limbic system, the amygdala is thought to connect sensory information to emotional responses. Its development, along with hormonal changes, may give rise to newly intense experiences of rage, fear, impulsivity, aggression (including toward oneself), excitement and sexual attraction.

As additional areas of the brain start to help process emotion, older teens gain some equilibrium and have an easier time interpreting others. But until then, they often misread teachers and parents (Feinstein, 2009). You can be as careful and sensitive as possible with your teen and yet have tears, anger and angst at times because they will have misunderstood what you have said.

Chemistry Lessons

Other chemical changes are also taking place in the brain during this period of flux.

For instance, there’s a peak in the brain’s sensitivity to dopamine – the neurotransmitter most responsible for feelings of pleasure.

The early adolescent brain, with its increased number of nerve cells, has higher levels of dopamine circulating in the prefrontal cortex, but dopamine levels in the reward centre of the brain (nucleus accumbens) alter throughout adolescence. These changes in the dopamine levels in the reward centre suggest that the adolescent requires more excitement and stimulation to achieve the same level of pleasure as an adult.

So the teenager will attempt riskier behaviours to achieve euphoria. Drug use, gambling, video gaming, pornography, and sexual experiences can all become addictive pursuits as the individual strives to accomplish a dopamine-mediated pleasure.

This vulnerability of the developing brain may well explain why these behaviours identified in adults often have their onset during adolescence or early adulthood.

The teen brain is similarly attuned to oxytocin – the “cuddle hormone” that makes social connections more desirable and rewarding, which is partly why teens perceive social rejection as almost a dire threat to their existence. To them, the feeling of rejection is visceral. And although they understand the risks of unprotected sex and joining gangs for instance, they tend to give more weight to the pleasures of belonging and inclusion than to their costs or consequences.

Next Instalment:
Building A Healthy Teenage Brain

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References:
Feinstein, S. (2009). Parenting the teenage brain: Understanding a work in progress. Maryland: Rowman and Littlefield Education.
Giedd, J. N. (2008). The teen brain: insights from neuroimaging. Journal of Adolescent Health, 42(4):335 – 343.

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