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Under Construction – The Adolescent Brain

Friday, November 8, 2013

By Lisa Levinson, Learning 2030 Blog Contributor

Most teenagers would not attribute their emerging selves to neurons, synapses, dendrites, axons, or anything else packed into their cranial locker.  Recent research on brain development has confirmed what parents, educators, and others who work with adolescents have intuitively known for years: the adolescent brain is a work in progress, and is being continuously shaped by experience. 

For about 20 years now, non-invasive brain imaging techniques (e.g. MRI scans) have allowed scientists to study brain development as a dynamic process. Behind the scenes, evidence shows that functional maturation coincides with the developmental milestones of childhood and adolescents. 

Image © MyBrainNotes

What's that you say?

Brain cells (neurons) talk to each other using an incredible electrical and chemical signaling system. When a neuron initiates a “conversation” it sends an electrical signal down its cable-like axon to the axon terminal. Here, the electrical energy is transformed into a chemical signal, in the form of specialized molecules that carry the neuron’s message to the next brain cell in line. The receiving neuron then generates its own electrical signal and continues down the line. Like the game "telephone," It takes a lot of practice to get the conversation “right.” After birth, development largely takes the form of changes in the number of connections gained and lost between neurons. The axons also become more specialized, and faster at transmitting their message. 

Experience is encoded in the brain in patterns of signals between neurons (nerve cells). Vast networks of neurons contribute to an individual’s ability to solve math problems, understand text, share ideas, create, and connect with others. These networks are influenced by experience – good or bad. 




From walking the walk to talking the talk

First to mature is the sensorimotor cortex, brain areas associated with voluntary movement and body sensation. This happens roughly around age 6. By age 10, the areas responsible for handling spatial, sensory, auditory, and language functions (the parietal and temporal association cortices) have reached maturity. 

Image © Headway

Brain areas that deal with more complex functions take even longer to reach maturity. The lateral temporal cortex, associated with language, memory and understanding, along with the prefrontal cortex, charged with “executive functioning”, begin reaching maturity around age 16.  

Executive functioning skills are essential for navigating a first romance (any relationship), managing competing home and school demands, persistence in the face of adversity, and setting realistic goals.  As with most construction projects, things don’t work as well as they will until the job is done; and we now know that connections to the prefrontal cortex continue to myelinate well into a person’s 20s. 

Keep in mind that “maturity” does not mean achieving full potential. Each individual has his or her own developmental course and mastery is the product of experience and practice. 

Five to twenty in six

To capture the course of development, researchers at NIH's National Institute of Mental Health and UCLA created a time-lapse 3D movie from a decade-long MRI Study of normal brain development (clicking link starts an .mpeg download). In less than six seconds, watch how the brain matures from ages 5 – 20. What you see is the how gray matter (a type of brain tissue that contains neurons and synapses) is refined over time. This maturation is believed to the result of a “pruning” process where unused connections in the brain are eliminated to make the pathways that remain more efficient. 

Nurture and nature

Many aspects of development are dictated by genetics, but environmental factors and experiences contribute significantly. Experience changes the brain on a structural level as a result of making new connections (synaptic formation), the branching of nerve cells to make more complex networks (dendritic arborization) and improving the speed at which information can travel within the brain and nervous system (through a process called myelination).

During adolescence, it is the prefrontal cortex that continues to develop. Because this continued brain development is highly adaptive, it makes adolescence a period of susceptibility as well as possibility.

Schizophrenia, for example, is a disorder that is most frequently diagnosed in the late teens and 20s, just as the prefrontal cortex is reaching maturity. Schizophrenia has multiple symptoms that can include a decreased ability to manage the processes supporting problem-solving, reasoning, and the planning/execution of actions. 

Other issues, including drug abuse, depression, suicide, and eating disorders, can surface during adolescence.  What remains to be seen is whether disruptions in brain functioning cause behavioral problems or if environmental factors contribute to brain dysfunction.  The answer will likely come from a better understanding of the dynamic interplay between genes and environmental factors. 

You get what you give

Adolescence is a time of great possibility for developing social and cognitive abilities. While different cultures place different demands on this life stage, we all must consider the challenges we face in the 21st century. If we feel that skills like critical and creative thinking, self-awareness, and a tolerance for failure are necessary for addressing the challenges of this century, then those are the experiences we should be providing. 

Lisa Levinson is a doctoral student in the Department of Biobehavioral Sciences and a Researcher at the Neurocognition of Language Lab, both at Teachers College, Columbia University.