Crime, Culpability and the Adolescent Brain

By Mary Beckman
www​.sci​encemag​.org

Crime, Culpability and the Adolescent Brain

This fall, the U.S. Supreme Court will con­sid­er whether cap­i­tal crimes by teenagers under 18 should get the death sen­tence; the case for lenien­cy is based in part on brain stud­ies.

When he was 17 years old, Christopher Simmons per­suad­ed a younger friend to help him rob a woman, tie her up with elec­tri­cal cable and duct tape, and throw her over a bridge. He was con­vict­ed of mur­der and sen­tenced to death by a Missouri court in 1994. In a whip­saw of legal pro­ceed­ings, the Missouri Supreme Court set the sen­tence aside last year. Now 27, Simmons could again face exe­cu­tion: The state of Missouri has appealed to have the death penal­ty rein­stat­ed. The U.S. Supreme Court will hear the case in October, and its deci­sion could well rest on neu­ro­bi­ol­o­gy.

At issue is whether 16- and 17-year-olds who com­mit cap­i­tal offens­es can be exe­cut­ed or whether this would be cru­el and unusu­al pun­ish­ment, banned by the Constitution’s eighth amend­ment. In a joint brief filed on 19 July, eight med­ical and men­tal health orga­ni­za­tions includ­ing the American Medical Association cite a sheaf of devel­op­men­tal biol­o­gy and behav­ioral lit­er­a­ture to sup­port their argu­ment that ado­les­cent brains have not reached their full adult poten­tial. ​“Capacities rel­e­vant to crim­i­nal respon­si­bil­i­ty are still devel­op­ing when you’re 16 or 17 years old,” says psy­chol­o­gist Laurence Steinberg of the American Psychological Association, which joined the brief sup­port­ing Simmons. Adds physi­cian David Fassler, spokesper­son for the American Psychiatric Association (APA) and the American Academy of Child and Adolescent Psychiatry, the argu­ment ​“does not excuse vio­lent crim­i­nal behav­ior, but it’s an impor­tant fac­tor for courts to con­sid­er” when wield­ing a pun­ish­ment ​“as extreme and irre­versible as death.“

The Supreme Court has addressed some of these issues before. In 1988, it held that it was uncon­sti­tu­tion­al to exe­cute con­victs under 16, but it ruled in 1989 that states were with­in their rights to put 16- and 17-year-old crim­i­nals to death. Thirteen years lat­er, it decid­ed that men­tal­ly retard­ed peo­ple should­n’t be exe­cut­ed because they have a reduced capac­i­ty for ​“rea­son­ing, judg­ment, and con­trol of their impuls­es,” even though they gen­er­al­ly know right from wrong (see side­bar on p. 599). That is the stan­dard Simmons’s lawyers now want the court to extend to every­one under 18.

Cruel and unusu­al?

Simmons’s lawyers argue that ado­les­cents are not as moral­ly cul­pa­ble as adults and there­fore should not be sub­ject to the death penal­ty. They claim that this view reflects world­wide ​“chang­ing stan­dards of decen­cy,” a trend that has been rec­og­nized in many U.S. courts. Today, 31 states and the fed­er­al gov­ern­ment have banned the juve­nile death penal­ty. The lat­est to do so, Wyoming and South Dakota, con­sid­ered brain devel­op­ment research in their deci­sions. Putting a 17-year-old to death for cap­i­tal crimes is cru­el and unusu­al pun­ish­ment, accord­ing to this rea­son­ing. ​“What was cru­el and unusu­al when the Constitution was writ­ten is dif­fer­ent from today. We don’t put peo­ple in stock­ades now,” says Stephen Harper, a lawyer with the Juvenile Justice Center of the American Bar Association (ABA), which also signed an ami­cus curi­ae brief. ​“These stan­dards mark the progress of a civ­i­lized soci­ety.“

The defense is focus­ing on the ​“cul­pa­bil­i­ty of juve­niles and whether their brains are as capa­ble of impulse con­trol, deci­sion-mak­ing, and rea­son­ing as adult brains are,” says law pro­fes­sor Steven Drizin of Northwestern University in Chicago. And some brain researchers answer with a resound­ing ​“no.” The brain’s frontal lobe, which exer­cis­es restraint over impul­sive behav­ior, ​“does­n’t begin to mature until 17 years of age,” says neu­ro­sci­en­tist Ruben Gur of the University of Pennsylvania in Philadelphia. ​“The very part of the brain that is judged by the legal sys­tem process comes on board late.“

But oth­er researchers hes­i­tate to apply sci­en­tists’ opin­ions to set­tle moral and legal ques­tions. Although brain research should prob­a­bly take a part in pol­i­cy debate, it’s dam­ag­ing to use sci­ence to sup­port essen­tial­ly moral stances, says neu­ro­sci­en­tist Paul Thompson of the University of California, Los Angeles (UCLA).

Shades of gray

Structurally, the brain is still grow­ing and matur­ing dur­ing ado­les­cence, begin­ning its final push around 16 or 17, many brain-imag­ing researchers agree. Some say that growth max­es out at age 20. Others, such as Jay Giedd of the National Institute of Mental Health (NIMH) in Bethesda, Maryland, con­sid­er 25 the age at which brain mat­u­ra­tion peaks. Various types of brain scans and anatom­ic dis­sec­tions show that as teens age, dis­or­dered-look­ing neu­ron cell bod­ies known as gray mat­ter recede, and neu­ron pro­jec­tions cov­ered in a pro­tec­tive fat­ty sheath, called white mat­ter, take over. In 1999, Giedd and col­leagues showed that just before puber­ty, chil­dren have a growth spurt of gray mat­ter. This is fol­lowed by mas­sive ​“prun­ing” in which about 1% of gray mat­ter is pared down each year dur­ing the teen years, while the total vol­ume of white mat­ter ramps up. This process is thought to shape the brain’s neur­al con­nec­tions for adult­hood, based on expe­ri­ence.

In argu­ing for lenien­cy, Simmons’s sup­port­ers cite some of the lat­est research that points to the imma­tu­ri­ty of youth­ful brains, such as a May study of chil­dren and teens, led by NIMH’s Nitin Gogtay. The team fol­lowed 13 indi­vid­u­als between the ages of 4 and 21, per­form­ing mag­net­ic res­o­nance imag­ing (MRI) every 2 years to track changes in the phys­i­cal struc­ture of brain tis­sue. As pre­vi­ous research had sug­gest­ed, the frontal lobes matured last. Starting from the back of the head, ​“we see a wave of brain change mov­ing for­ward into the front of the brain like a for­est fire,” says UCLA’s Thompson, a co-author. The brain changes con­tin­ued up to age 21, the old­est per­son they exam­ined. ​“It’s quite pos­si­ble that the brain mat­u­ra­tion peaks after age 21,” he adds.

The images showed a rapid con­ver­sion from gray to white mat­ter. Thompson says that researchers debate whether teens are actu­al­ly los­ing tis­sue when the gray mat­ter dis­ap­pears, trim­ming con­nec­tions, or just coat­ing gray mat­ter with insu­la­tion. Imaging does­n’t pro­vide high enough res­o­lu­tion to dis­tin­guish among the pos­si­bil­i­ties, he notes: ​“Right now we can image chunks of mil­lions of neu­rons, but we can’t look at indi­vid­ual cells.” A type of spec­troscopy that picks out N‑acetylaspartate, a chem­i­cal found only in neu­rons, shows promise in help­ing to set­tle the issue. In addi­tion to grow­ing vol­ume, brain stud­ies doc­u­ment an increase in the orga­ni­za­tion of white mat­ter dur­ing ado­les­cence. The joint brief cites a 1999 study by Tomás Paus of McGill University in Montreal and col­leagues that used struc­tur­al MRI to show that neu­ronal tracts con­nect­ing dif­fer­ent regions of the brain thick­ened as they were coat­ed with a pro­tec­tive sheath of myelin dur­ing ado­les­cence (Science, 19 March 1999, p. 1908).

In 2002, anoth­er study revealed that these tracts gained in direc­tion­al­i­ty as well. Relying on dif­fu­sion ten­sor MRI, which fol­lows the direc­tion that water trav­els, Vincent Schmithorst of the Children’s Hospital Medical Center in Cincinnati, Ohio, and col­leagues watched the brain orga­nize itself in 33 chil­dren and teens from age 5 to 18. During ado­les­cence, the tracts fun­neled up from the spinal tract, through the brain­stem, and into motor regions. Another linked the two major lan­guage areas. ​“The brain is get­ting more orga­nized and dense with age,” Schmithorst says.

Don’t look at the light

Adults behave dif­fer­ent­ly not just because they have dif­fer­ent brain struc­tures, accord­ing to Gur and oth­ers, but because they use the struc­tures in a dif­fer­ent way. A ful­ly devel­oped frontal lobe curbs impuls­es com­ing from oth­er parts of the brain, Gur explains: ​“If you’ve been insult­ed, your emo­tion­al brain says, ​‘Kill,’ but your frontal lobe says you’re in the mid­dle of a cock­tail par­ty, ​‘so let’s respond with a cut­ting remark.’ ​“

As it matures, the ado­les­cent brain slow­ly reor­ga­nizes how it inte­grates infor­ma­tion com­ing from the nether regions. Using func­tion­al MRI-which lights up sites in the brain that are active-com­bined with sim­ple tests, neu­ro­sci­en­tist Beatriz Luna of the University of Pittsburgh has found that the brain switch­es from rely­ing heav­i­ly on local regions in child­hood to more dis­trib­u­tive and col­lab­o­ra­tive inter­ac­tions among dis­tant regions in adult­hood.

One of the meth­ods Luna uses to probe brain activ­i­ty is the ​“anti­sac­cade” test: a sim­pli­fied mod­el of real-life respons­es designed to deter­mine how well the pre­frontal cor­tex gov­erns the more prim­i­tive parts of the brain. Subjects focus on a cross on a screen and are told that the cross will dis­ap­pear and a light will show up. They are told not to look at the light, which is dif­fi­cult because ​“the whole brain­stem is wired to look at lights,” says Luna.

Adolescents can pre­vent them­selves from peek­ing at the light, but in doing so they rely on brain regions dif­fer­ent from those adults use. In 2001, Luna and col­leagues showed that ado­les­cents’ pre­frontal cor­tices were con­sid­er­ably more active than adults’ in this test. Adults also used areas in the cere­bel­lum impor­tant for tim­ing and learn­ing and brain regions that pre­pare for the task at hand.

These results sup­port oth­er evi­dence show­ing that teens’ impulse con­trol is not on a par with adults’. In work in press in Child Development, Luna found that vol­un­teers aged 14 years and old­er per­form just as well on the task as adults, but they rely main­ly on the frontal lobe’s pre­frontal cor­tex, where­as adults exhib­it a more com­plex response. ​“The ado­les­cent is using slight­ly dif­fer­ent brain mech­a­nisms to achieve the goal,” says Luna.
Although the work is not cit­ed in the brief, Luna says it clear­ly shows that ​“ado­les­cents can­not be viewed at the same lev­el as adults.“

Processing fear

Other stud­ies-based on the amyg­dala, a brain region that process­es emo­tions, and research on risk aware­ness-indi­cate that teenagers are more prone to errat­ic behav­ior than adults. Abigail Baird and Deborah Yurgelun-Todd of Harvard Medical School in Boston and oth­ers asked teens in a 1999 study to iden­ti­fy the emo­tion they per­ceive in pic­tures of faces. As expect­ed, func­tion­al MRI showed that in both ado­les­cents and adults, the amyg­dala burst with activ­i­ty when pre­sent­ed with a face show­ing fear. But the pre­frontal cor­tex did­n’t blaze in teens as it did in adults, sug­gest­ing that emo­tion­al respons­es have lit­tle inhi­bi­tion. In addi­tion, the teens kept mis­tak­ing fear­ful expres­sions for anger or oth­er emo­tions.

Baird, now at Dartmouth College in Hanover, New Hampshire, says that sub­se­quent exper­i­ments showed that in teenagers the pre­frontal cor­tex buzzes when they view expres­sions of peo­ple they know. Also, the chil­dren iden­ti­fied the cor­rect emo­tion more than 95% of the time, an improve­ment of 20% over the pre­vi­ous work. The key dif­fer­ence between the results, says Baird, is that ado­les­cents pay atten­tion to things that mat­ter to them but have dif­fi­cul­ty inter­pret­ing images that are unfa­mil­iar or seem remote in time. Teens shown a dis­co-era pic­ture in pre­vi­ous stud­ies would say, ​“Oh, he’s freaked out because he’s stuck in the ​’70s,” she says. Teens are painful­ly aware of emo­tions, she notes.

But teens are real­ly bad at the kind of think­ing that requires look­ing into the future to see the results of actions, a char­ac­ter­is­tic that feeds increased risk-tak­ing. Baird sug­gests: Ask some­one, ​“How would you like to get roller skates and skate down some real­ly big steps?” Adults know what might hap­pen at the bot­tom and would be wary. But teens don’t see things the same way, because ​“they have trou­ble gen­er­at­ing hypothe­ses of what might hap­pen,” says Baird, part­ly because they don’t have access to the many expe­ri­ences that adults do. The abil­i­ty to do so emerges between 15 and 18 years of age, she the­o­rizes in an upcom­ing issue of the Proceedings of the Royal Society of London.

Luna points out that the tumul­tuous nature of ado­les­cent brains is nor­mal: ​“This tran­si­tion in ado­les­cence is not a dis­ease or an impair­ment. It’s an extreme­ly adap­tive way to make an adult.” She spec­u­lates that risk-tak­ing and low­ered inhi­bi­tions pro­vide ​“expe­ri­ences to prune their brains.“

With all the prun­ing, myeli­na­tion, and reor­ga­ni­za­tion, an ado­les­cen­t’s brain is unsta­ble, but per­form­ing well on tests can make teens look more mature than they are. ​“Yes, ado­les­cents can look like adults. But put stres­sors into a sys­tem that’s already frag­ile, and it can eas­i­ly revert to a less mature state,” Luna says.

The ami­cus curi­ae brief endorsed by the APA and oth­ers also describes the fragili­ty of ado­les­cence-how teens are sen­si­tive to peer pres­sure and can be com­pro­mised by a less-than-pris­tine child­hood envi­ron­ment. Abuse can affect how nor­mal­ly brains devel­op. ​“Not sur­pris­ing­ly, every [juve­nile offend­er on death row] has been abused or neglect­ed as a kid,” says ABA attor­ney Harper.

Biology and behav­ior

Although many researchers agree that the brain, espe­cial­ly the frontal lobe, con­tin­ues to devel­op well into teen­hood and beyond, many sci­en­tists hes­i­tate to weigh in on the legal debate. Some, like Giedd, say the data ​“just aren’t there” for them to con­fi­dent­ly tes­ti­fy to the moral or legal cul­pa­bil­i­ty of ado­les­cents in court. Neuroscientist Elizabeth Sowell of UCLA says that too lit­tle data exist to con­nect behav­ior to brain struc­ture, and imag­ing is far from being diag­nos­tic. ​“We could­n’t do a scan on a kid and decide if they should be tried as an adult,” she says.

Harper says the rea­son for bring­ing in ​“the sci­en­tif­ic and med­ical world is not to per­suade the court but to inform the court.” Fassler, who staunch­ly oppos­es the juve­nile death penal­ty, does­n’t want to pre­dict how the case will turn out. ​“It will be close. I’m hope­ful that the court will care­ful­ly review the sci­en­tif­ic data and will agree with the con­clu­sion that ado­les­cents func­tion in fun­da­men­tal­ly dif­fer­ent ways than adults.” And per­haps, advo­cates hope, top­pling the death penal­ty with a sci­en­tif­ic under­stand­ing of teenagers will spread to bet­ter ways of reha­bil­i­tat­ing such youths.

SIDEBAR

Adolescence: Akin to Mental Retardation?

The human brain took cen­ter stage in 2002 when the U.S. Supreme Court ruled against the death penal­ty for men­tal­ly retard­ed per­sons. In that case (Atkins v. Virginia), six of the nine jus­tices agreed that exe­cut­ing a con­vict with lim­it­ed intel­lec­tu­al capac­i­ty, Daryl Atkins, would amount to cru­el and unusu­al pun­ish­ment. Instructing the state of Virginia to for­go the death penal­ty in such cas­es, Justice John Paul Stevens wrote: ​“Because of their dis­abil­i­ties in areas of rea­son­ing, judg­ment, and con­trol of their impuls­es, [men­tal­ly retard­ed per­sons] do not act with the lev­el of moral cul­pa­bil­i­ty that char­ac­ter­izes the most seri­ous adult crim­i­nal con­duct.“

When the case of Christopher Simmons, who com­mit­ted mur­der at age 17, comes before the same jus­tices in October, says law pro­fes­sor Steven Drizin of Northwestern University in Chicago, defense attor­neys hope to equate juve­nile cul­pa­bil­i­ty to that of men­tal­ly retard­ed per­sons. ​“Juveniles func­tion very much like the men­tal­ly retard­ed. The biggest sim­i­lar­i­ty is their cog­ni­tive deficit. [Teens] may be high­ly func­tion­ing, but that does­n’t make them capa­ble of mak­ing good deci­sions,” he says. Brain and behav­ior research sup­ports that con­tention, argues Drizin, who rep­re­sents the Children and Family Justice Center at Northwestern on the ami­cus curi­ae brief for Simmons. The ​“stan­dard of decen­cy” today is that teens do not deserve the same extreme pun­ish­ment as adults.

The Atkins deci­sion pro­vides advo­cates with a ​“tem­plate” for what fac­tors should be laid out to deter­mine ​“evolv­ing stan­dards of decen­cy,” says Drizin. These fac­tors include the move­ment of state leg­is­la­tures to raise the age lim­it for the death penal­ty to 18, jury ver­dicts of juve­nile offend­ers, the inter­na­tion­al con­sen­sus is on the issue, and pub­lic opin­ion polls. In 2002, the court also con­sid­ered the opin­ions of pro­fes­sion­al orga­ni­za­tions with per­ti­nent knowl­edge, which is how the brain research comes into play. Last, the jus­tices con­sid­ered evi­dence that the men­tal­ly retard­ed may be more like­ly to false­ly con­fess and be wrong­ly convicted‑a prob­lem that ado­les­cents have as well.

-M.B.