March 30, 2007
 
HEALTH AND MEDICINE: Just As You Suspected, Teen Brains Not Fully Developed
 
By Lee Bowman
Scripps Howard News Service
 
Brain researchers are increasingly confirming what auto-insurance actuaries have long known -- the powers of decision-making, especially under stress, don't fully mature in most people until they are in their mid-20s.
 
Boatloads of sophisticated imaging studies and other research show that the frontal lobe of the brain -- the part involved in judgment, organization, planning and strategizing -- gets all its gray matter by age 11 or 12. But the myriad connections from the frontal part aren't completely wired to function like an adult for at least another decade.
 
Imaging studies also suggest that because the braking system of the frontal lobe is still developing, signals from the primal emotions in the brain tend to get the upper hand.
 
Research indicates that using drugs or alcohol may not only disrupt the brain's tools for judgment in the short term, but also interferes with the long-term developmental process.
 
Jay Giedd, an imaging researcher at the National Institutes of Health, says for teens, "doing drugs or alcohol that evening, it may not just be affecting their brains for that night or even for that weekend, but for the next 80 years of their life."
 
Several research projects reported in recent weeks emphasize how important this final round of brain organization and pruning can be.
 
First, researchers at the University of Illinois in Champaign reported results from a study of adolescent rats that showed a substantial loss of neurons in the ventral prefrontal cortex, which is devoted to planning and social behavior.
 
While earlier studies in people had shown there are gradual reductions in the volume of this part of the brain in adolescence, "the finding that neurons are actually dying is completely new," said Janice Juraska, a professor of psychology and lead investigator of the study published in the Feb. 8 issue of the journal Neuroscience. "Some major changes are occurring in adolescence that no one suspected."
 
She suspects it is no accident that psychological conditions like schizophrenia and depression often develop at this point in life, and that addictions that begin at this stage are harder to overcome than those that start in adulthood.
 
Another small study on brain-damaged patients, by researchers at Harvard University and several other institutions, found that those who had lost function in the ventromedial prefrontal cortex, a center of empathy and social emotions, were more willing than those with damage elsewhere or with no damage to make coldhearted decisions.
 
For instance, they had no misgivings about killing a person infected with HIV if that was the only option to prevent others from becoming infected. That study appeared last week in the journal Nature.
 
At Emory University, researchers led by Dr. Greg Berns are pursuing yet another culprit in the adolescent decision-making process -- excess of the brain-signaling chemical dopamine.
 
"We propose that the reason that teenagers sometimes make bad decisions is because the reward system in their brains is hyperactive," said Berns, an associate professor in psychiatry and behavioral science.
 
"Studies in both humans and other animals have suggested that the dopamine system peaks in activity during adolescence. If this is true, the abundance of dopamine might lead to different considerations of short-term and long-term rewards and consequences," he said.
 
Other research has already shown that when dopamine levels are too high, the chemical can cause distorted perceptions of reality and trigger dangerous risk-taking.
 
With funding from the National Institute on Drug Abuse, Berns and colleagues are starting a new round of functional magnetic resonance imaging testing of teens to study how the dopamine system interacts with other parts of the brain during different types of decisions teens confront.
 
Specifically, they'll watch how different areas of the brain respond as teenagers weigh risk and reward for different types of things that are important to them -- money, music and food -- as well as how peer pressure impacts those decisions.
 
On the Net: www.nida.nih.gov
 
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