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Demysti ing thE

Adolescents can be mature one moment and frustratingly immature the next. The nature of brain development helps explain why.

Laurence Steinberg

n addition to being a transitional time and our understanding of brain maturation in physical, intellectual, emotional, has grown at breathtaking speed. Major and social development, adolescence contributions to our understanding have is a time of important changes in the come from studies using functional magnetic sn-ucture and function of the brain. resonance imaging (fMRI). This teclmique . ScientistsI are beginning to understand how enables researchers to take pictures of indi­ the psychological changes of adolescence are viduals' brains and compare anatomy (brain linked to brain maturation. structure) and activity (brain function). Before the development of brain imaging Some aspects of brain development in technology, scientists could only speculate adolescence are reflected in changes in brain about the workings of the adolescent brain. structure (for instance, certain parts of the Now, however, with the same scanners that brain are relatively smaller in childhood are used to identify tumors and tom liga­ than in adolescence, whereas other parts ments, researchers can see inside the adoles­ are relatively larger). Other aspects of brain cent's brain and watch what happens when development are reflected in changes in brain teenagers think. We now know that, other Junction (for instance, adolescents may use than the first three years of life, no period of different parts of the brain than children do development is characterized by more dra­ when performing the same task). matic brain changes than adolescence. In addition, greater interconnectedness among various regions of the brain allows for What We've Learned from fMRI better communication between parts asso­ It used to be thought that improved intel­ ciated with different functions. For example, lectual functioning in adolescence would be connections between regions of the brain reflected in larger brain size. However, the responsible for logical reasoning become brain has reached its adult size by age 10, better connected with those responsible for making it impossible that changes in thinking experiencing intense emotions; "cross-talk" during adolescence are the result of sheer between these regions enables better impulse increases in the brain's size or volume. control and self-regulation. That's one reason Since 2000, there's been an explosion in that older teenagers are so much better than research on adolescent brain development, younger ones at controlling their emotions. - L

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)' You may have had an MRI exam to whether the ways in which the presence opment is the development of connec­ diagnose the underlying cause of some of friends changes brain activity differs tions-synapses- between neurons. By sort of pain. Although the technology between teenagers and adults. We've age 2, a single neuron may have 10,000 used in this sort of imaging is the found that the mere presence of peers connections to other neurons. The for­ same as that used by neuroscientists activates adolescents' reward centers­ mation of some synapses is genetically who study brain development, the "f' but not those of adults. This may make programmed, but others are formed in fMRI refers to the use of the test teenagers more inclined to take risks through experience. The rate of synapse to examine how the brain functions, when they're with their friends because formation peaks at about age 1 and and not just its anatomy. Researchers they're more likely to focus on the slows down in early childhood, but the use fMRI to examine patterns of brain rewards of a risky choice than on the development of new synapses continues activity while individuals perfonn a spe- potential costs. throughout life as we learn new skills, build memories, acquire knowledge, and adapt to changing circumstances.1

Synaptic Pruning Initially, the brain produces many more connections among cells than it will use. The number of synapses in the brain of a 1-year-old is about twice the number in the adult brain. However, soon after birth, unused and unnecessary synapses start to be eliminated, a process called synaptic pruning. As a general rule, we tend to assume that "more is better," but that's not the case here. Imagine a meadow between two patches of forest. Hundreds of lightly trodden paths connect one side to the other (the unpruned brain). Over time, people dis­ cover that one path is more direct than cific task (for example, recalling a list of A Primer on Brain M aturation others. More people begin using this words, viewing photos of one's friends, Synapse Formation path more often, so it becomes wider or listening to music). Participants in an The human brain contains approxi­ and deeper. Because the other paths are fMRI study are asked to perform tasks mately 100 billion neurons, cells that not used anymore, the grass grows back on a computer while they lie inside carry information by transmitting elec­ and those paths disappear. That's what a brain scanner. With this setup, it's trical charges within the brain by means synaptic pruning is like. possible to study both how patterns of chemicals called neurotransmitters. The elimination of synapses con­ of brain activity differ during different Neurons do not actually touch; there's tinues through adolescence and is tasks (for example, when we actively a miniscule gap between them called normal and necessary to development read as opposed to being read to) and a synapse. When the electrical charge and functioning. j ust as pruning a rose whether people of different ages show travels through a neuron, it stimu- bush-cutting off weak and misshapen different patterns of brain activity while lates the release of neurotransmitters, branches- produces a healthier plant performing the same task. Many of the chemicals that carry the signal across with larger flowers, so synaptic pruning most important brain changes that take the synapse from one neuron to the enhances the brain's functioning. It place during adolescence are not in the next. Anytime we perceive somed1ing makes the brain more efficient by trans­ brain's structure, but in how the brain (for example, feel an itch); move some­ forming an unwieldy network of small works. thing (scratch the itch); or process infor­ pathways into a better organized system At Temple University, we're studying mation (wonder where the itch came of superhighways. how patterns of brain activity vary when from), this process of electrical trans­ In general, the development of syn­ individuals perform tasks either alone or mission is involved. apses is characterized by a period of with their friends watching them, and A key process in early brain devel- growth (when more and more synapses ?'-·- :; 7 --rl .. ~r .ll · ·\o I • _I I t ' i . . ' -i! ~ ; ~--- myelin encases the projec­ Imaging studies have also shown called dopamine is responsible for the tions of neurons that interconnect them, important changes in the functioning feeling of pleasure. When something a process called myelination . Myelin, of the prefrontal cortex in adolescence. enjoyable happens, we experience what which acts like plastic insulation around Patterns of activation within the pre­ some scientists have called a "dopamine an electrical wire, increases the speed frontal cortex typically become more squirt," which leads to the sensation of of neural impulses and so improves focused. For instance, in experiments pleasure. It makes us want whatever information transmission. Myelination in which participants are presented elicited the squirt because the feeling of occurs in waves, beginning in the with a rapid succession of images and pleasure it produces is so strong. (Some prenatal period and continuing into asked to push a button when a certain stimuli produce so much pleasure that adulthood. As with synaptic pruning, image appears but refrain from pushing we get a dopamine squirt just.antici­ examining where myelination occurs it when a different image appears, ado­ pating the experience.) most dramatically at a particular point lescents are less likely than children to We now know there's a rapid increase in development provides clues about activate prefrontal regions that are not in dopamine activity in early adoles­ the aspects of cognitive functioning that relevant to performing the task well. cence-in fact, there's more dopamine are changing most at that stage. In addition, individuals become more activity in the brain's reward center in likely to use multiple parts of the brain early adolescence than at any other time What This Means for the simultaneously and coordinate activity of life. Because things feel especially Adolescent Brain among prefrontal regions and other pleasurable during early adolescence, More Advanced Reasoning. .. areas of the ·brain, such as the limbic young adolescents go out of their way to During adolescence, the brain is system, a region that's important for our seek rewarding experiences. At all ages remodeled through synaptic pruning experience of reward and punishment we seek out things that make us feel and myelination in particular brain and for processing emotional and social good, of course. But the drive to do this regions. The most important part of the information, such as reading someone's is much more intense in early adoles­ brain to be pruned in adolescence is the facial expression or judging what a cence than before or after. prefrontal cortex, the region of the brain person thinks of us. The urge to seek out rewarding and directly behind your forehead, which pleasurable experiences is a mixed is most important for sophisticated But More Rish Tahing blessing. On the plus side, it's part of thinking abilities, such as planning, At the same time that the adolescent what makes it so much fun to be a thinking ahead, and weighing risks brain is maturing in ways that enable teenager. But sometimes this drive is and rewards. There's also continued teenagers to become more capable of so intense that adolescents can exhibit myelination of the prefrontal cortex reasoned thinking, it's also changing in a sort of reward tunnel vision. They're and its connections to other pans of the ways that make them do risky things. so driven to seek pleasure that they brain throughout adolescence, which Do you remember how good your may not pay attention to the associated leads to many cognitive advances, first passionate kiss felt7 How much you tisks. To teenagers, driving fast, having including improvements in our ability loved the music that was popular when unprotected sex, and drinking alcohol ·-- ;rr;=;;r •r •· . - I

feel so good that thoughts about a teenagers who get straight As in algebra the maturation of the brain systems speeding ticket (or worse), an unwanted can also do really dumb things when responsible for thinking ahead and pregnancy, or being grounded for out with their buddies. controlling impulses is influenced by coming home smelling of beer may not Teachers sometimes are surprised by the sorts of experiences young people even make it onto their radar screen. the inconsistency in students' behavior, have, including their experiences in the This combination of advanced (but especially dming the middle school classroom. Given the well-documented not yet totally mature) reasoning and years. Understanding the nature of finding that practicing something will heightened sensation-seeking explains brain development in adolescence helps strengthen the brain circuits that control why otherwise intelligent adolescents explain why adolescents can vacillate that behavior, it's important that, as often do surprisingly foolish things. so often between mature and immature educators, we provide adolescents More important, the fact that teen­ behavior. When it comes to more with opportunities to practice things agers' ability to control their impulses basic abilities, such as those involving like planning, anticipating the conse­ is immature at the same time that their memory, attention, and logical rea­ quences of a decision, and regulating interest in sensation seeking is stronger soning, especially under optimal condi- their own behavior. Although it can than ever makes them vulnerable to making mistakes. Early adolescence is like starting a car without having a Just as pruning a rose bush produces skilled driver behind the wheel. a healthier plant, so synaptic pruning What This Means for Adolescent Behavior enhances the brain's functioning. Although scientists agree about the ways in which the structure and function of tions, the average 15-year-old is just be frustrating to teachers and parents the brain change during adolescence, the as mature as the average adult. But when young adolescents push for more implications of these changes for ado­ research on brain maturation indicates autonomy, we need to respond by lescent development are still the subject that relatively more sophisticated cog­ gradually granting them more control. of a great deal of ongoing research and nitive abilities, such as thinking ahead, Assignments that require teenagers to considerable speculation. I'm often envisioning the consequences of a think ahead, make a plan, and carry asked when adolescents begin to think decision, balancing risks and rewards, it out may stimulate the maturation of like adults. This is hard to answer on or controlling impulses, are still devel­ brain systems that enable more mature the basis of brain science alone because oping at that age. self-regulation. it depends on which aspects of thinking Initially, adolescents who haven't you're concerned about. The Need to Practice Autonomy been given many opportunities to lt's important to keep in mind that the develop these capabilities may not Both Mature and Immature brain is very malleable, or "plastic," and always succeed. But be patient. Over Psychologists draw a distinction that its development is affected by expe­ time, with practice, as synapses are between "cold" cognition (when we lience as well as biology. Both synaptic pruned and neural circuits myelinated, think about something that doesn't have pruning and myelination are influenced adolescents' ability to exercise mature much emotional content, like how to by experience, such that repeated acti­ control over their own behavior will solve an algebra problem) and "hot" vation of a specific collection of neurons improve. m cognition (when we think about some­ as a result of engaging in a particular 1 Steinberg, L., Vandell, D., & Bomstein, thing that can make us feel exuberant behavior will actually strengthen the M. (2011). Development: Infancy through ado­ or excited, angry or depressed, like connections among those neurons, lescence. Belmont, CA: Wadsworth. whether to go joyriding with friends which, in tum, will make them function or throw a punch at someone who more efficiently. This is one reason that Laurence Steinberg is the Distinguished insulted a girlfriend). The systems of practicing the same task over and over University Professor of Psychology at the brain responsible for cold cognition again makes that task easier to perform Temple University, Philadelph ia, Penn­ are mature by the time most individuals each time. sylvania, and the author of You and are 16. But tpe systems that control hot Although research on brain plas­ Your Adolescent: The Essential Guide cognition aren't-they're still devel­ ticity during adolescence is just in its for Ages 10 to 25 (Simon and Schuster, oping well into the 20s. That's why infancy, many scientists believe that 201 1); [email protected].