May 11, 2004: Scripps Howard News Service

New research shows stark differences in teen brains

By Lee Bowman

Recent pop­u­lar films depict­ing teenagers sud­den­ly housed in adult bod­ies have more than a lit­tle truth in them.

The lat­est brain research has found strong evi­dence that when it comes to matu­ri­ty, orga­ni­za­tion and con­trol, key parts of the brain relat­ed to emo­tions, judg­ment and ​“think­ing ahead” are the last to arrive.

“It seems that reg­u­la­tion of impulse con­trol is the last on board and often the first to leave in the brain as we age,” said Dr. Ruben Gur, a pro­fes­sor of psy­chol­o­gy and direc­tor of the Brain Behavior Laboratory at the University of Pennsylvania who has been research­ing brain devel­op­ment in young adults.

Until recent­ly, most brain experts thought the human com­mand cen­ter stopped grow­ing at around 18 months, and that neu­rons were pret­ty much set for life by age 3.

In fact, the brain’s gray mat­ter has a final growth spurt around the ages of 11 to 13 in the frontal lobes of the brain, the regions that guide human intel­lect and planning.

But it seems to take most of the teen years for young­sters to link these new cells to the rest of their brains and solid­i­fy the mil­lions of con­nec­tions that allow them to think and behave like adults.

At the same time, the release of a cas­cade of ado­les­cent hor­mones dur­ing and after puber­ty caus­es oth­er areas of the brain, par­tic­u­lar­ly the amyg­dala, which gov­erns basic emo­tion­al response, to fire up or expand.

The result is that teens look at things dif­fer­ent­ly than adults. This has tremen­dous impli­ca­tions for edu­ca­tion, men­tal health, drug abuse and moral and legal respon­si­bil­i­ty of adolescents.

Deborah Yurgelun-Todd of Harvard Medical School and McClean Hospital in Boston has stud­ied how teenagers and adults respond dif­fer­ent­ly to the same images. Shown a set of pho­tos of peo­ple’s faces con­tort­ed in fear, adults named the right emo­tion, but teens sel­dom did, often say­ing the per­son was angry.

When Yurgelun-Todd and her team did the same test while doing func­tion­al mag­net­ic res­o­nance imag­ing of the sub­jec­t’s brains, they found a stark dif­fer­ence in the parts being used. Adults used both the advanced pre­frontal cor­tex and the more basic amyg­dala to eval­u­ate what they had seen; younger teens relied entire­ly on the amyg­dala, while old­er teens (top age in the group was 17) showed a pro­gres­sive shift toward using the frontal area of the brain.

“Just because teens are phys­i­cal­ly mature, they may not appre­ci­ate the con­se­quences or weigh infor­ma­tion the same way as adults do,” Yurgelun-Todd said. ​“Good judg­ment is learned, but you can’t learn it if you don’t have the necessary hardware.”

There is more evi­dence of the differences:

A recent imag­ing study by researchers at the National Institute on Alcohol Abuse and Alcoholism found that teens tak­ing an exper­i­men­tal gam­bling test are less like­ly to acti­vate a region in the base of the brain that moti­vates behav­ior to work to obtain rewards than a con­trol group of young adults, ages 22 – 28, play­ing the same games.

Numerous stud­ies show alco­hol and per­haps oth­er drugs hit teen brains hard­er than they do adult brains. The frontal lobes and the hip­pocam­pus, which is involved in mem­o­ry for­ma­tion, are particularly vulnerable.

It has been known for some time that chil­dren have sharp growth spurts in brain con­nec­tions among regions spe­cial­ized for lan­guage and spa­tial rela­tion­ships between ages 6 and 12. That lan­guage capac­i­ty tends to reside most­ly in a per­son­’s non­dom­i­nant side — the left hemi­sphere of the brain in right-han­ders, for instance. But a recent imag­ing study by researchers at the University of Cincinnati Medical Center found that this dis­tinc­tion ends in the mid-20s when the brain shifts to use both sides in language processing.

The sto­ry of teen brain devel­op­ment lies in a process called myelin­iza­tion, in which a lay­er of fat coats wire-like fibers con­nect­ing regions of the brain, back-to-front, side-to-side, and every­where in between. Over time, this makes the oper­a­tion of the brain more pre­cise and effi­cient, affect­ing not just think­ing and prob­lem-solv­ing, but also coor­di­na­tion and mas­tery of skills rang­ing from throw­ing a base­ball to play­ing the trombone.

But there’s a price for this greater effi­cien­cy ‑brain cells that aren’t hooked up to oth­er parts tend to get killed off.

“If they’re not on the net­work, they die and their place is tak­en up with cere­bral flu­id. This goes on well beyond age 18,” said Dr. David Fassler, a psy­chi­a­trist at the University of Vermont.

Even in adult­hood, the wiring job is not com­plete­ly done. Imaging done on the brains of peo­ple in their 40s and 50s show there’s anoth­er surge of con­nec­tions being made, per­haps in response to menopause or to pre­pare the brain to bet­ter com­pen­sate for the loss of brain cells as we age.

Still, it’s a slow, ardu­ous road to matu­ri­ty and insight for teens.

“We have some new insight into the 16 year-old that does­n’t think twice about get­ting in a car with a friend who’s been drink­ing, but they’re still not going to appre­ci­ate adults argu­ments for why they should­n’t,” said Fassler.

At the National Institute of Mental Health, Dr. Jay Giedd, who helps run the ongo­ing imag­ing stud­ies that first detect­ed the mid­dle school growth spurt, said the new under­stand­ing of teen brains ​“argues for doing a lot of things as a teenag­er. You are hard-wiring you brain in ado­les­cence. Do you want to hard-wire it for sports and play­ing music and doing math­e­mat­ics, or for lying on the couch in front of the television?”

The new under­stand­ing of ado­les­cent brains leads to ques­tions of ethics and legalities.

The Supreme Court already has decid­ed that peo­ple should not be exe­cut­ed for crimes com­mit­ted when they were age 15 or younger, and in the fall is sched­uled to con­sid­er whether the restric­tion should be extend­ed to every­one under 18.

Two years ago, the court banned exe­cu­tion of men­tal­ly retard­ed peo­ple because of defi­cien­cies that ​“dimin­ish their personal culpability.”

“With the new bio­log­i­cal expla­na­tion that ado­les­cent brains are dif­fer­ent, we think there’s sci­en­tif­ic evi­dence that they, too, are less cul­pa­ble,” said Stephen Harper, an adjunct pro­fes­sor of juve­nile jus­tice at the University of Miami School of Law who spe­cial­izes in capital cases.

Gur said some sci­en­tists would put off the age of legal major­i­ty to 22 or 23, and said there will like­ly be con­sid­er­able debate over how to tell when a per­son­’s brain phys­i­cal­ly looks like an adult’s as imag­ing research con­tin­ues and efforts to set stan­dards and norms develop.

Fassler pre­dicts that with­in a decade, brain images will be sophis­ti­cat­ed enough to ​“help us deter­mine the age for appro­pri­ate treat­ment of addic­tions and ther­a­py mod­els for adults and ado­les­cents with disorders.”

Other researchers say that while it’s pos­si­ble to gain gen­er­al under­stand­ing about brain devel­op­ment and func­tion from the images, the notion that med­i­cine, law enforce­ment or any­one else should work from some ide­al, nor­mal brain mod­el is troubling.

“Each indi­vid­ual is not an exact map, and the dif­fi­cul­ties in deter­min­ing what the range of vari­a­tions are is real­ly dan­ger­ous. The data is incred­i­bly easy to be over-inter­pret­ed,” said Sonia Miller, a New York attor­ney who spe­cial­izes in cas­es deal­ing with new technologies.

Some courts are already accept­ing brain scans as evi­dence of a per­son­’s men­tal capac­i­ty in crim­i­nal cas­es, she said, and ​“as the neu­ro­science of inten­tion­al behav­ior devel­ops, the way we assign respon­si­bil­i­ty and blame will be chal­lenged. This rais­es a lot of ques­tions about how much neur­al pri­va­cy can we expect, how much the author­i­ties can get into your brain.”

Dr. Peter Bandettini, a brain-imag­ing researcher at the National Institutes of Health, said the sci­ence of under­stand­ing what small struc­tures and chem­i­cals are doing with­in the brain is far from a gold stan­dard for men­tal func­tion or age.

“Right now, I per­son­al­ly think you’d get more infor­ma­tion about a per­son­’s men­tal age by going to a set of behav­ioral tests. But I’d agree that as these tech­nolo­gies become more pow­er­ful, there’s going to be a greater need for checks and bal­ances to deter­mine how the imag­ing infor­ma­tion should be used.”

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