First off, kids enterting puberty experience a big drop in their ability to read the emotions of others. So suddenly the likelihood for misunderstandings shoots way up:
Robert McGivern and his team of neuroscientists at San Diego State University found that as children enter puberty, their ability to quickly recognise other people's emotions nosedives. What's more, this ability does not return to normal until they are around 18 years old. McGivern reckons this goes some way towards explaining why teenagers tend to find life so unfair, because they cannot read social situations as efficiently as others.
Previous studies have shown that puberty is marked by sudden increases in the connectivity of nerves in parts of the brain. In particular, there is a lot of nerve activity in the prefrontal cortex. "This plays an important role in the assessment of social relationships, as well as planning and control of our social behaviour," says McGivern.
He and his team devised a study specifically to see whether the prefrontal cortex's ability to function altered with age. Nearly 300 people aged between 10 and 22 were shown images containing faces or words, or a combination of the two. The researchers asked them to describe the emotion expressed, such as angry, happy, sad or neutral.
The team found the speed at which people could identify emotions dropped by up to 20 per cent at the age of 11. Reaction time gradually improved for each subsequent year, but only returned to normal at 18 (Brain and Cognition, vol 50, p 173).
During adolescence, social interactions become the dominant influence on our behaviour, says McGivern. But at just the time teenagers are being exposed to a greater variety of social situations, their brains are going through a temporary "remodelling", he says. As a result, they can find emotional situations more confusing, leading to the petulant, huffy behaviour adolescents are notorious for.
This study may not have used subjects with an early enough starting age to detect the initial decline in ability detected in the previous study:
Another series of MRI studies is shedding light on how teens may process emotions differently than adults. Using functional MRI (fMRI), a team led by Dr. Deborah Yurgelun-Todd at Harvard's McLean Hospital scanned subjects' brain activity while they identified emotions on pictures of faces displayed on a computer screen.5 Young teens, who characteristically perform poorly on the task, activated the amygdala, a brain center that mediates fear and other "gut" reactions, more than the frontal lobe. As teens grow older, their brain activity during this task tends to shift to the frontal lobe, leading to more reasoned perceptions and improved performance. Similarly, the researchers saw a shift in activation from the temporal lobe to the frontal lobe during a language skills task, as teens got older. These functional changes paralleled structural changes in temporal lobe white matter.
During a time period when teens are already having a hard enough time sorting thru their own emotions they become far more sensitive to emotion-altering recreational drugs:
Researchers at Jefferson Medical College have evidence in animals that the young, adolescent brain may be more sensitive to addictive drugs such as cocaine and amphetamines than either the adult or newborn. The work may help someday lead to a better understanding of how the adolescent human brain adapts to such drugs, and provide clues into changes in the brain that occur during drug addiction.
Scientists led by Michelle Ehrlich, M.D., professor of neurology at Jefferson Medical College of Thomas Jefferson University in Philadelphia and a member of the Farber Institute for Neurosciences at Jefferson, and Ellen Unterwald, Ph.D., associate professor of pharmacology at the Temple University School of Medicine in Philadelphia, found a greater increase in a certain protein in the part of the adolescent mouse brain called the striatum following chronic exposure to drugs such as amphetamine or cocaine than they did in either very young mice or adults.
Such psychostimulant drugs affect the brain's striatum in different ways, potentially affecting both movement and locomotion, or the "reward" system. This "molecular adaptation," says Dr. Ehrlich, could be significant. "An increase in this protein may be important because it could also affect other molecules that could lead to long-lasting changes in the brain in response to psychostimulant drugs." The protein, called Delta FosB, is a transcription factor and plays a role in regulating gene expression. Earlier research by other scientists had shown increased amounts of Delta FosB in adult brains following chronic exposure to psychostimulants.
The team, which includes scientists at the Nathan Kline Institute in Orangeburg, New York, reports its findings November 1 in the Journal of Neuroscience.
Teens are at risk of developing life long harmful habits and their brains change in a way to puts them at greater risk of developing addiction to the demon weed:
When they did, researchers at Duke University found that adolescent brains respond more intensely to nicotine. The scientists injected rats with nicotine every day for more than two weeks, a dose comparable to what a typical smoker receives. In all of the rats the number of chemical receptors dedicated to nicotine increased -- a sign of addiction. But in adolescents, the number of nicotine receptors increased twice as much compared to adults.
"What we found is that the adolescent brain gets a lot more bang for the buck," says Theodore Slotkin, one of the scientists who performed the research.
A follow-up study published in the October issue of Brain Research showed that adolescent nicotine exposure caused permanent behavioral problems as well, especially for females. Even after two weeks with no nicotine, female rats were less interested in moving around and raising their young than counterparts who had never been exposed.
That may be because nicotine retards cell division in the hippocampus, a brain region that continues growing into adulthood in females, but not males.
The larger society is forcing teenagers to wake up earlier than their teen biological clocks are telling them to:
When teenagers insist that they are not tired at 9 or 10 p.m., they are very likely telling the truth. For reasons that are not fully understood, Dr. Carskadon said, their body clocks shift, so that their natural tendency is to stay up later at night and wake up later in the morning than when they were younger. But that inner clock often clashes with the outer world: early starting times in high school and demanding schedules of sports, clubs, music lessons, homework and part-time jobs.
There are consequences. For one thing, lack of sleep can interfere with learning: tired students have a hard time paying attention, and even if they do somehow manage to focus, they may forget what they were taught because memory formation takes place partly during sleep.
In "Adolescent Sleep Patterns," a book published in August and edited by Dr. Carskadon, she wrote, "The students may be in school, but their brains are at home on their pillows."
What's worse, the types of brain activities engaged in during adolescence probably have a significant impact on what cognitive abilities people will have the rest of their lives:
Even though it may seem that having a lot of synapses is a particularly good thing, the brain actually consolidates learning by pruning away synapses and wrapping white matter (myelin) around other connections to stabilize and strengthen them. The period of pruning, in which the brain actually loses gray matter, is as important for brain development as is the period of growth. For instance, even though the brain of a teenager between 13 and 18 is maturing, they are losing 1 percent of their gray matter every year.
Giedd hypothesizes that the growth in gray matter followed by the pruning of connections is a particularly important stage of brain development in which what teens do or do not do can affect them for the rest of their lives. He calls this the "use it or lose it principle," and tells FRONTLINE, "If a teen is doing music or sports or academics, those are the cells and connections that will be hardwired. If they're lying on the couch or playing video games or MTV, those are the cells and connections that are going to survive."
On the bright side, the spurts in cell growth in various parts of the brain during adolescence open up the possibility of therapies to boost intelligence by developing hormonal and/or gene therapies that would make the burst of nerve growth more intense. Also, with better understanding it may become possible to structure the institutions that deal with adolescents to better accommodate the developmental stages of their brains. Obviously, just moving starting times forward for schools is a fairly easy accommodation.
Update: These results provide a sense of just how much the mind changes during adolescence:
Researchers at studied the post-mortem cerebral cortexes of six 12- to 17-year-olds and five 17- to 24-year-olds. All of the individuals had been of normal health and intelligence. They studied 43 different areas in each brain hemisphere, measuring for cortical thickness, neuronal density and pyramidal neuronal size. Corrections were made for gender differences in the size of the brain.
The average pyramidal soma size was 15.5 percent smaller in the older age group than in the younger one. This suggests that these nerve cells undergo “pruning” or “streamlining” of their processing during adolescence, said de Courten-Myers.
Other measures of the brain were slightly larger in the older age group, including cortical thickness (1.9 percent), neural density (1.8 percent), the number of neurons/standard cortical columns (3.8 percent), neuropil volume/standard cortical column (3.1 percent), and neuropil volume/neuron (1.3 percent).
A National Institutes of Health study suggests that the region of the brain that inhibits risky behavior is not fully formed until age 25, a finding with implications for a host of policies, including the nation's driving laws.
"We'd thought the highest levels of physical and brain maturity were reached by age 18, maybe earlier -- so this threw us," said Jay Giedd, a pediatric psychiatrist leading the study, which released its first results in April. That makes adolescence "a dangerous time, when it should be the best."
So that is why teenagers are so reckless. Hardly comforting news. You can know this and they will still be reckless after all.
|Share |||Randall Parker, 2002 November 12 12:20 PM Brain Development|