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“What Makes Teens Tick” by C. Wallis, A. Park Review Essay (Article)

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Updated: Oct 13th, 2021


A flood of hormones. The brain store structural changes. Is this what makes adolescence exciting and exasperating?

Five young men enter a waiting room in the National Institute of Health center in Bethesda. They take their seats in a classic collapsed -teenager mode, that is trailing backpacks, CD players, and laptops with computer games. It’s mid-afternoon and they should be tired but their presence changes the atmosphere of the institution. The two sets of twins Corey and Skyler Mann 16, Antony and Brandon 18, and their big brother Christopher 22 are here to have their scan. The five brothers are the latest recruits to join the giant study founded in 1991. Its goal is to study the development of the brain.

Dr. Jay Giedd, chief of brain imaging in the institute, has devoted 13 years to operating 1800 kids and teenagers using Magnetic resonance imaging (MRI). He creates a unique photo album for each volunteer by taking MRI snapshots every two years and builds a record as the brain grows. He started investigating the origins of attention-deficit/hyperactivity disorder (ADHD) and autism. He discovered that little was known about how the brain is supposed to develop and impossible to figure out where things might go wrong. This project is his attempt to establish a gigantic control group. “Normal brains are interesting, but adolescents’ studies are most surprising”, he marvels.

Before Geidds project, most scientists believed that the brain was a finished product by the age of twelve. It is not only fully grown in size but also in cognitive development, this is according to Swiss psychologist Jean Piaget. Giedds project proved that the brain undergoes extensive changes well past adolescence. To show that the brain of an adolescent is far from maturity.

The MRI is helping researchers to figure out whether the physiological changes might affect the behavior of adolescents, which include emotional outbursts, reckless risk-taking, rule-breaking, the impassioned pursuit of sex, drugs, and rock n roll. Some experts relate the timing of mental illnesses such as schizophrenia and bipolar to these changes. These disorders contribute to high rates of teen suicide. Wild behavior is associated with two factors: raging hormones and lack of cognitive controls needed for maturity.

Geidds study has shifted to twins which is why the Manns were recruited. Brain development follows a set plan which changes following pre-programmed cues. Changes in gray matter are affected by experience and environment. He hopes to follow twins whose brains are similar at birth but the programming changes as they take different paths in life. He hopes to find the influence of nature and nurture. Antony Manns plan to become a pilot and Brandon’s, a lawyer, will bring about differences in the brain which will be detected by the MRI.

The brothers go through various tests throughout the afternoon.

MRI involves removing all metallic objects from the body then an oil-filled capsule which is opaque is placed on the left cheek and ear. It helps to define a plane on the image. The test takes fifteen minutes and involves three tests. The first is a quick scan, the second look for damages and any abnormalities and takes two minutes, and finally the ten minutes test. The machine scans 124 thin slices. The computer takes 20 hours to process the images.

MRI does not involve any radiation thus making the study of healthy children possible.

Construction Ahead

The brain grows very little during childhood. By age 6 the brain is 90%-95% of its adult size. Humans have the maximum brain-cell density between the third-sixth month. The final month before birth the unnecessary brain cells are eliminated (pruning) and thus scientists believe that autism occurs if the unnecessary cells are not properly eliminated.

In the late teens, the second wave of pruning occurs. Unlike prenatal changes, this affects the number of connections between the cells. At age 6 to 12 the neurons grow bushier and the connections are many and the white matter thickens. This thickening grows between age 11 for girls and 12 ½ for boys. At this time the second wave of pruning is underway. Gray matter is a shade off at 0.7% per year. During adolescence, there are fewer but faster connections.

Scientists believe that pruning is a result of two principles: genetics and use it or lose it. Gerald Edelman described the process as “Neural Darwinism”. The cerebellum which coordinates the physical and mental activities responds to experience. But Geidd is not sure what drives the build-up or pruning process. The study of twins will help to determine this.

The development of any brain follows the same stages. The back part of the brain reaches maturity faster through pruning and proliferation than the front part. The back part of the brain is in direct contact with the environment, it controls the senses. The final part of the brain to mature is the prefrontal cortex, the part capable of reasoning and decision making.

Raging Hormones

Scientists say that bad decisions that are made by teenagers are caused by hormones. But MRI studies have shown that the part responsible for decision making is not yet mature during adolescence.

All the same, hormones remain a crucial factor in the teen’s brain. During this time the ovaries and testes start producing hormones-estrogen and testosterone. Studies have shown that adrenal sex hormones are active in the brain. They affect the serotonin and other neurochemicals that regulate mood and excitability. They affect the emotional center of the brain. That is why teenagers seek to thrill and excitement. This is because the brain is still under construction.

Dumb Decisions

During adolescence, the brain is still maturing and this explains some of the decisions made by teenagers. The fMRI (functional magnetic resonance imaging) is able to show the brain when a person is still working. During an experiment, it was clear that adolescents use their emotions while adults use judgment. The emotional outburst of teenagers can then be understood in this sense.

In another experiment, it was clear that peer pressure affects teenagers. Individually a teenager is able to make the right decision. Teenagers are normally affected by their emotions.

Teenagers are also affected by dopamine-a brain chemical involved in motivation and reinforcement. This makes teenagers more vulnerable. It is usually active in the teen years. The front part of the brain of teenagers is usually inactive. This is responsible for motivation. Any action that has rewards is encouraged by the teenagers.

Melatonin a chemical responsible for sleep takes longer to rise in teenagers than in adults. This is why teens have a problem sleeping.

Pruning Problems

Scientists believe that ADHD and Tourette’s syndrome is related to the brain proliferation period. Though both disorders have genetic roots rapid growth of brain tissue in childhood can cause increased motor skills. Symptoms recede during adolescence.

Schizophrenia is associated with two things: abnormal pruning of the prefrontal cortex (teenagers lose close to 15 percent cortical gray matter while those who develop schizophrenia lose about 25%) or prenatal origin but it is hidden as pruning takes place.

What Parents Should Know

Teenagers do not have much conscious control. Therefore parents should help them by organizing their time, guiding them through tough decisions even when they are resistant, and just be patient and love their teenagers.


Wallis, C. & Park, A. (2004), What makes Teens Tick, 163(19), 56-65.

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