One day a child is cheerful, loving and obedient, comes to a parent or teacher for advice, dresses in appropriate clothing, and turns in for the night at 10:00pm. Homework is done without nagging and parent/teacher conferences are a joy. Then somewhere between ten and twelve, a strange thing happens. Almost over night it appears someone has unzipped this child and put someone else inside. No longer could this child be called sweet and loving; surly and antagonistic would be better descriptors. Gone are the days when they ask for advice and if it is offered, you can be certain it will be ignored. This teen comes to breakfast in the morning dressed in an outfit on which you would like to pin a note stating, “What this person is wearing to school today is not my idea of good taste!” The teen spends hours on the computer, but homework doesn’t get done and teacher/parent conferences are no longer pleasant.
It doesn’t take a brain scientist to tell you that adolescents can be frustrating. Most of us understand that the teen’s life is shaped by factors such as family, friends, school, and community institutions. But there are also powerful neurological issues at play. Neuroscience has made great strides in shedding light on the changes occurring in the teen’s brains and why they behave the way they do. Interestingly, the new information focuses not only on the oft-blamed raging hormones, but on what’s going on above the neck as well. Many of the new insights into the adolescent brain have been gained using the brain-imaging techniques that were discussed in Chapter One. What the scientists are seeing is that the teen years are a time of significant change in the activity, anatomy and neurochemistry of the brain.
As we have seen, the brain grows by expanding and pruning the connections between cells, keeping the connections that are used the most and getting rid of the unused ones. We have also seen that one of the most active periods of reorganization occurs early in life around two years of age when there is a huge build up of neural connections in the child’s brain. Recall that this build up is followed by a massive pruning which allows the strongest and most efficient connections to function more effectively. Until recently, scientists assumed that this period of growth and winnowing away occurs only in early childhood and that most, if not all, of the major changes in brain organization and development occurred before adolescence. This view seemed reasonable in the light of the fact that the brain reaches its full size by puberty. The conventional wisdom had been that the adolescent brain is fully developed and functions similarly to an adult brain. This turns out–as many middle-school teachers and parents already suspected–not to be the case. Instead scientists have discovered that very complex changes are taking place in the brain during adolescence and that the brain is not fully “installed” until between ages twenty to twenty-five. The brain is still changing during the teen years!
Changes in the Adolescent Brain
In what parts of the adolescent brain are the greatest changes occurring? A central area of focus has been the frontal lobes. A long-range study by Jay Giedd and his colleagues at the National Institutes of Mental Health (NIMH.) has involved using functional Magnetic Resonance Imaging (fMRI) to scan the brains of nearly 1000 healthy children and adolescents aged 3 to 18. Giedd discovered that just prior to puberty, between ages 9 and 10, the frontal lobes undergo a second wave of reorganization and growth (Giedd, 2007). This growth appears to represents millions of new synapses. Then around age eleven a massive pruning of these connections takes place which isn’t complete until early adulthood. Recall that although it may seem like the more synapses, the better, the brain actually consolidates learning by pruning away connections. The brain is getting rid of the least-used pathways, a method for ensuring that the most useful synapses are maintained which in turn allows the brain to operate more efficiently.
In addition to this winnowing of connections in the adolescent brain, another developmental factor is also at play. One of the final steps in developing an adult brain is myelination. Recall that myelin develops in the more primitive areas of the brain first, gradually moving to the higher level functioning areas. Myelin increases the speed of the axon potential traveling down the axon, up to 100 fold compared to neurons that have no myelin. So, during the teen years not only does the number of connection change, the speed of the connections becomes faster. It is not surprising then to find that myelination occurs in the frontal lobes last. Researchers at the University of California at Los Angeles compared scans of young adults, 23 – 30, with those of teens, 12 – 16, looking for signs of myelin which would imply more mature, efficient connections. As expected, the frontal lobes in teens showed less myelination than in the young adults. This is the last part of the brain to mature: full myelination is probably not reached until around age 30 or perhaps later.
Why are these changes in the frontal lobes significant? The frontal lobes–specifically the area right behind the forehead called the prefrontal or orbitofrontal cortex–is often referred to as the CEO of the brain. It is in this part of the brain that executive decisions are made and where ethical/moral behavior is mediated. In fact, this part of the brain has been dubbed “the area of sober second thought.” Persons with damage to this part of the brain often know what they are supposed to do but are unable to do it. In these persons the damage also appears to impair their ability to imagine the future consequence of their actions. They tend to be more uninhibited and impulsive. Observations such as these suggest that teens may have difficulty inhibiting inappropriate behaviors because the circuitry need for such control is not fully mature. The chart below [Need #} summarizes the cognitive and behavioral functions of the prefrontal cortex.
- Organization of multiple tasks
- Impulse inhibition
- Self control
- Setting goals and priorities
- Empathizing with others
- Initiating appropriate behavior
- Making sound judgments
- Forming Strategies
- Planning ahead
- Adjusting behavior when situation changes
- Stopping an activity upon completion
These functions are practically a laundry list of characteristics that adolescents often lack. Many researchers suspect that an unfinished prefrontal cortex, with its excess of synapses and unfinished myelination, contributes to the adolescent’s deficits in these areas. Their brains often aren’t ready to take on the role of the CEO, resulting in a lack of reasoned thinking and performance.
Another factor is at play in the adolescent brain that sheds some light on their often over-emotional behavior. Scientists have discovered that in the teen brain, the emotional center matures before the frontal lobes. Emotion therefore often holds sway over rational processing. When we realize that the prefrontal cortex allows reflection while the amygdala is designed for reaction, we can begin to understand the often irrational and overly emotional reactions of teens. Our oft-asked question when teens engage in irrational behavior, “What were you thinking?” is difficult for teens to answer because in many cases they weren’t thinking reflectively; they were reacting impulsively. This phenomenon has been further validated by a team led by Dr. Deborah Yurgelun-Todd at Harvard’s McLean Hospital. They used functional Magnetic Resonance Imaging (fMRI) to compare the activity of adolescent brains to those of adults. They found that when identifying emotional expressions on faces, adolescents activated the amygdala more often than the frontal lobes. The opposite was seen in adults. In terms of behavior, the adult’s responses were more intellectual while the teens responses were more from the gut or more reactive. Giedd comments that adolescents can be thought of as trucks with no brakes!
The neurotransmitter dopamine plays an important role in the often reckless, sensation seeking behavior of adolescents. Recall that dopamine is a naturally produced stimulant. It is critical for focusing attention on the environment especially when there are conflicting options. When a goal is not obvious, reflection, not impulse, is necessary to make a good decision. Early in adolescent development levels are relatively low which may account for their reactive behavior. The good news is that dopamine inputs to the prefrontal cortex grow dramatically as the teen ages, resulting in an increased capacity for more mature judgment and impulse control. But until this system is mature, decisions are often made on impulse.
Substance Abuse During Adolescence
Now that it has become clear that, in contrast to previously-held assumptions, there is a tremendous amount of change taking place in the teen brain, we need to look at the possibility that alcohol and other drugs impact both brains and behavior differently in adolescents and adults. The shaping and fine-tuning of the frontal lobes is, at least in part, mediated by experience. This raises the possibility that drug abuse could alter normal development of the brain. This is an area of critical importance. Current estimates suggest that roughly 50% of high school seniors consume alcohol at least once a month while 17% regularly smoke cigarettes and nearly 50% have smoked some marijuana (Kann et al, 2000: Johnston et al., 2001). The National Institute of Alcoholism and Alcohol Abuse reports that alcohol kills six and a half times more individuals under age 21 than all other drugs combined.
Much of the research on the effects of alcohol has been conducted using animal studies. In studies of rats, Markwiese et al. (1998) found that alcohol disrupts the activity of an area of the brain essential for memory and learning, the hippocampus, and that this area is are much more vulnerable to alcohol-induced learning impairments in adolescent rats than adult rats. Rats are not humans, however, there is some evidence that the human hippocampus reacts in a similar manner. A recent study by De Bellis et al. (2000) found that hippocampal volumes were smaller in those who abused alcohol during adolescence and that the longer one abused alcohol, the smaller the hippocampus became.
Research by Sandra Brown and colleagues at the University of California, San Diego has produced the first concrete evidence that heavy, on-going alcohol use by adolescents can impair brain functioning. They found several differences in memory function between alcohol dependent and non-drinking adolescents, none of whom used any other drugs. In the study, the 15 and 16 year-olds who had drunk heavily (more than 100 lifetime alcohol use episodes) scored lower on verbal and nonverbal retention of information.
Additional research by Brown and Tappert (2000) is trying to answer is whether or not heavy drinking at 15 is more dangerous for the brain than at 20. Their preliminary hypothesis is that drinking may be more dangerous because the finishing touches on brain development (myelination and pruning) haven’t been completed and alcohol may interrupt or disturb these refining processes. Brown and Tappert point out that more studies will be needed to produce a definitive answer, but at least their work is an important step toward confirming what many scientists have suspected for some time, teenagers who drink may be exposing their brains to the toxic effects of alcohol during a critical time in brain development.
Not only are the frontal lobes of adolescents going through major changes, the molecular and chemical systems are being re-shifted as well. Many substances appear to have a heightened effect on teens. Researchers at Duke University found that adolescent brains respond more intensely to nicotine than do adult brains. In rat brains, the levels of dopamine receptors in the pleasure center (the nucleus accumbens) of the brain increase dramatically between 25-40 days–the rat’s adolescent phase (Spears, 2000). These receptors play a huge role in the pleasure producing properties of drugs. It is not yet clear if the human adolescent brain evidences this same increase, but many researchers think it is highly probable.
Adolescent Sleep Patterns
A common complaint of parents of teenagers is that their kids insist they can’t fall asleep until midnight but every morning means yelling at them to get out of bed in time to get to school on time. And parents aren’t the only ones with complaints about adolescents’ sleep habits. Teachers of early morning classes complain that their students seem to be in class in body only, frequently nodding off or at the least, drowsy and difficult to teach. It may not be the teens’ fault; biology may be behind their sleep problems. Recent research has shown that here is yet another area where adolescents’ brains move to the beat of a different drummer.
Our sleep cycles are determined by what is called circadian rhythms, a sort of internal biological clock that determines not only how much sleep we need but also when we become sleepy at night and when we awaken in the morning. Sleep researcher, Mary Carskadon in her sleep laboratory at Brown University’s Bradley Hospital, has discovered that teenagers need more sleep than they did as children and that their circadian rhythms appear to be set later than those of children or adults.
The conventional wisdom has been that young children need 10 hours sleep and that as we become adults, the need decreases to 8 hours. Teenagers have been included in the adult group. Carskadon has shown that teens, far from needing less sleep than they did as children, need more. In order to function well and remain alert during the day, they need 9 hours and 15 minutes, possibly because the hormones that are critical to growth and sexual maturation are released mostly during sleep. One survey of the sleep patterns of 3,000 teenagers showed that the majority slept only about 7-hours a night with more than a quarter averaging 6-hours or less on school nights. Given that sleep is a time when brain cells replenish themselves and when connections made during the day are strengthened, sleep deprivation can have a major negative effect on learning and memory.
A second finding from Carskadon’s research is that these teens’ biological clocks appear to be set later than those of children or adults. They do not get sleepy as early as they did when they were preadolescents and therefore tend to stay up later at night and sleep later in the morning. Most teenagers’ brains aren’t ready to wake up until 8 or 9 in the morning, well past the time when the first bells has sounded at most high schools. Teens who have to get up before their internal clock buzzes, miss out on an important phase of REM sleep that is important for memory and learning.
Not all scientists agree totally with the research on the adolescent brain. Giedd’s theory that brain changes are responsible for the often erratic behavior we see in teens is speculative. The theory is somewhat controversial because the roots of behavior are complex and cannot be easily explained by relatively superficial changes in the brain. However, if the theory turns out to be true, it would underscore the importance of providing careful guidance through adolescence, which isn’t a bad idea in any case. Giedd states “…unlike infants whose brain activity is completely determined by their parents and environment, the teens may actually be able to control how their own brains are wired and sculpted.” Adolescents are laying down neural foundations for the rest of their lives. As parents and teachers, we have an opportunity and an obligation to educate adolescents about what is going on in their brains and the role they play determining the structure and functioning of their brains for the rest of their lives.
Teaching the Adolescent
Later chapters in this book will focus on brain-compatible strategies designed for various ages, however given the unique characteristics of adolescents, it seems appropriate to take a look some general considerations which may help teachers when they plan classroom instruction for these students.
In a sense the adolescents’ brains are primed to learn, however we often see boredom and apathy in their behavior. When we consider the hyperactivity of the amygdala and high energy level at this stage of brain development this isn’t surprising. Too much classroom instruction is “sit and git,” adolescents’ least favorite classroom activity! Very few teens like to sit still and listen to a teacher deliver a lecture. While lectures are sometimes appropriate during the teen years, consider having the students use interactive note-taking guides. After hearing or reading new information, students can be asked to demonstrate their understanding of the content by various methods such as role play, poster demonstrations, teaching another student or writing their reflections in a journal. Most parents will attest to the fact that adolescents like to argue. This propensity can be put to good use in debates where students discuss the pros and cons of complex ethical issues. Project-based activities are especially motivating to teens. In collaborative groups they can be encouraged to seek answers to problems facing the school or community, perhaps interviewing other teachers, parents or adults for their points of view. When concepts have been learned, it is helpful to give students real-life problems to solve that require the use of the concepts.
Few of us are as proficient in current technology as adolescents. They text, download music and information on ipods, and surf the internet with ease. Teachers should consider ways to integrate teens’ ability to use technology in the classroom. Given the option, students might prepare multi-media presentations rather than book reports or use email to dialog with experts in biology, history, music, mathematics, neuroscience, or other fields of study. The internet provides a speedy manner for researching topics for term papers and projects however with its increasing use many students will need guidance in determining the validity of the data. Reading “URLs” may become one of the new basic skills for anyone capable of using a computer to obtain information.
Teens are full of promise. They are energetic, caring and capable of making many contributions to their communities. They are also able to make remarkable spurts in intellectual development and learning. But we must remember; they are not adults and need to be taught in a manner that enables their brains to make sense of information, to see what they are learning as relevant to their lives.
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