New Studies of Adolescent Brains Challenge Assumptions

These new findings may enable doctors to create better treatments for young people, help teachers design and assess assignments, allow parents to understand their children better and help young people deal with the stresses of changing bodies and brains.

According to Jay Giedd, a neuroscientist at the National Institute of Mental Health who recently spearheaded research about growth and change in the adolescent brain, "[It's] not that the teens are stupid or incapable of [things]. It's sort of unfair to expect them to have adult levels of organizational skills or decision making before their brain is finished being built."

New gray matter has a big effect

	Synapses transmit electric brain signals between neurons.

While the human brain is called the most complicated 3-pound mass in the universe, there are some certainties about it. The brain produces neurons, brain cells and synapses -- the connections between cells. Originally, it was thought much of human brain development happened in the womb and the first few years of life, and that by age six, the brain was 95 percent of its adult size and structure.

Scientists have now pinpointed a second wave of production of neurons and synapses in the adolescent brain during puberty.

Perhaps most surprisingly, while young people continue to produce gray matter they are also pruning connections in the brain causing an overall reduction of gray matter of 1 percent a year during their teens, "much like a tree growing extra branches, twigs and roots" says Dr. Giedd.

Teen brain’s ‘CEO’ is not fully developed

	The brain's prefrontal cortex controls decision-making.

Dr. Giedd found that the prefrontal cortex, the part of the brain right behind the forehead that is involved in planning, working memory, organization and modulating mood -- often referred to as the CEO of the brain -- continues to grow and change throughout puberty. It is the last area of the brain to develop, which means that while teens become highly functional in other areas, they cannot reason as well as adults.

In a separate study, Dr. Yurgelun-Todd at McLean Hospital in Belmont, Mass., studied how teenage brains understood the emotions of others around them. While looking at pictures of adults with shocked faces, the teens mostly used the amygdala, a small region that guides instinctual reactions, while the adults relied on the frontal cortex. Beginning in the early 20s, the center of activity shifted more toward the frontal cortex and away from the cruder response of the amygdala.

Legal, health and behavior implications

	Some people think that teenagers should not be tried as adults because their brains are not fully developed.

The researchers argue that their findings have implications for public policy and juvenile justice.

The frontal lobe is "involved in behavioral facets germane to many aspects of criminal culpability," explains Dr. Ruben C. Gur, neuropsychologist and director of the Brain Behavior Laboratory at the University of Pennsylvania.

“The evidence now is strong that the brain does not cease to mature until the early 20s in those relevant parts that govern impulsivity, judgment, planning for the future, foresight of consequences and other characteristics that make people morally culpable…. Indeed, age 21 or 22 would be closer to the ‘biological’ age of maturity,” Gur said. 

The research also suggests that drug and alcohol addiction have different effects on adolescent brains.

With the frontal lobe not fully attached and developed, young people can be drawn to sensation-seeking behaviors, such as rollercoasters, driving fast or drug experimentation.

Dr. Frances Jensen a pediatric neurologist at Boston Children’s Hospital says "Addiction has been shown to be essentially a form of 'learning…[so drugs are] tapping into a much more robust habit-forming ability that adolescents have, compared to adults."

Dr. Geidd explains that adolescence brains are in a “use it or lose it stage.” He told PBS’ Frontline “So if a teen is doing music or sports or academics, those are the cells and connections that will be hard-wired. If they're lying on the couch or playing video games or MTV, those are the cells and connections that are going [to] survive.”