Age of Reason, continued...
Sep. 10th, 2007 06:26 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
semiotic_pirateEarlier today, I made a post where I mentioned the “age of reason” in an offhand manner. The age I quoted was 25, according to a source I couldn’t remember. I was called on that; and I decided to go digging around to see what I could see. Ruby Rod would be proud. Super-green?
I have culled evidence from various sites. Enjoy!
Wisdom teeth, also known as third molars, are the last teeth to erupt in your mouth. This generally occurs between the ages of 17 and 25, a time of life that has been called the "Age of Wisdom." Via The American Association of Oral and Maxillofacial Surgeons.
According to the Catholic Church, as quoted from the Catholic Encyclopedia, the age of reason is defined as follows:
The name given to that period of human life at which persons are deemed to begin to be morally responsible. This, as a rule, happens at the age of seven, or thereabouts, though the use of reason requisite for moral discernment may come before, or may be delayed until notably after, that time. At this age Christians come under the operation of ecclesiastical laws, such as the precept of assistance at Mass on Sundays and holy days, abstinence from meat on certain days, and annual confessions, should they have incurred mortal sin. The obligation of Easter Communion literally understood applies to all who have reached "the years of discretion"; but according to the practical interpretation of the Church it is not regarded as binding children just as soon as they are seven years old. At the age of reason a person is juridically considered eligible to act as witness to a marriage, as sponsor at baptism or confirmation, and as a party to the formal contract of betrothal; at this age one is considered capable of receiving extreme unction, of being promoted to first tonsure and minor orders, of being the incumbent of a simple benefice (beneficium simplex) if the founder of it should have so provided; and, lastly, is held liable to ecclesiastical censures. In the present discipline, however, persons do not incur these penalties until they reach the age of puberty, unless explicitly included in the decree imposing them. The only censure surely applicable to persons of this age is for the violation of the clausura of nuns, while that for the maltreatment, suadente diabolo, of clerics is probably so.
I did end up finding the source of my use of 25 years old as the Age of Reason, it is an NIH study described in this Washington Post article about brain immaturity and its relation to vehicular crashes. I’ve quoted bits and pieces below, the full article is at the end of the post:
By most physical measures, teenagers should be the world's best drivers. Their muscles are supple, their reflexes quick, their senses at a lifetime peak. Yet car crashes kill more of them than any other cause -- a problem, some researchers believe, that is rooted in the adolescent brain.
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.
About as thick and wide as a silver dollar, the region (the dorsal-lateral prefrontal cortex, just behind the brow) distinguishes humans from other animals. From it, scientists believe, come judgments and values, long-term goals, the weighing of risks and consequences -- what parents call wisdom or common sense and what science calls "executive functions."
While society and tradition have placed the point of intellectual maturity, the "age of reason," years earlier, the study -- an international effort led by NIH's Institute of Mental Health and UCLA's Laboratory of Neuro Imaging -- shows it comes at about age 25.
The process is generally completed a year or two earlier in women but varies greatly from person to person. Why that is, Giedd said, "we still don't know."
The pattern probably serves an evolutionary purpose, he said, perhaps preparing youths to leave their families and fend for themselves, without wasting energy worrying about it.
The findings imply that many life choices -- college and career, marriage and military service -- often are made before the brain's decision-making center comes fully online.
Temple's Steinberg said the NIH/UCLA research supports his theory that teen recklessness is partly the result of a critical gap in time -- starting with the thrill-seeking that comes in puberty and ending when the brain learns to temper such behavior. Since children today reach puberty earlier than previously, about age 13, and the brain's reasoning center doesn't reach maturity until the mid-twenties, Steinberg said, "this period of recklessness has never been as long as it is now."
Apparently, rental car companies agree with the 25 year old “Age of Reason” since they don’t rent to anyone under that age, and if they do, you’d have to be at least 21 and pay a sometimes hefty surcharge. Because of the high accident rate associated with drivers under 25 (and the severity of those incidents), "car-rental companies don't think it's worth the risk to rent to this age group," says William Maloney, chief operating officer for the American Society of Travel Agents.
An interesting anecdotal story found here about the stages we pass through as described by SAPARMURAT TURKMENBASHY THE GREAT (1940-2006):
In August 2002, the president of Turkmenistan, Saparmurat Niyazov, who's generally referred to by your average Turkman as "Turkmenbashi the Great," decreed that the country would change its perspective on how its citizens view aging. It's interesting to compare this worldview with our Euro-American take on time.
Turkmenbashi the Great, whom I will refer to as Niyazov for short, has defined and divided the Ages of Man into nine segments, each of which is a dozen or so years long. This lifetime calendar has stretched the potential life span to an optimistic 109 years, although statistics show a peculiar tendency of the average Turkman to come up about 49 years short of that goal.
The president declares that "childhood" shall last for 13 years from birth. That's pretty much what we in the West say, too.
Then come the years 14-25, which Niyazov categorizes as "adolescence." Here we begin to diverge in perspective. While there's not much disagreement about the initial teen year, thanks to such enlightened and progressive industrial world advancements as food laced with growth hormones and a popular media which uses sex to sell everything from soup to - er - nuts, our adolescence tends to end at, say, age 15. Then you're an adult, if not legally then certainly physically and attitudinally.
After adolescence comes a dozen years of "youth," terminating at 37. I can't think of anyone I know in that age bracket who would care to disagree with that definition, although some of their cardiologists might.
Until age 49, one enjoys the "Age of Maturity." Again, it's hard to disagree with the definition, although there is the bizarre Western tendency toward immaturity in the later stages of this phase. We call it "mid-life crisis," but obviously we may have to adjust that as acceptance of the Niyazov Numbers becomes more widespread.
An amusing pun comes forth in the next phase, the "Age of the Prophet," which lasts until one's 62nd year. Again, this closely follows our Western outlook, with only a spelling change to make it "Profit" instead.
Then the "Age of Inspiration" kicks in. This also is encouraging, especially for Turkmen, since this is greater than their actual expected life span. Nothing like a little inspiration to keep you going.
Starting at 73 comes the age of the "White Bearded Elder." Providing one still has hair, this time of one's life could be quite ego flattering.
And here's good news for the federal pension plan: under the Turkmen calendar "Old Age" doesn't kick in until age 85. This, of course, conflicts by two decades with our own definition. But you don't need to be an actuary to see how our country could benefit financially by delaying old-age benefit payments until people reached this new, imaginative chronological benchmark.
Next, at 97, Turkmenbashi the Great pays homage to Oguz Khan, an ancient figure who led his country presumably up until age 109. This will be, Niyazov declares, a person's "Age of Oguz Khan."Perhaps Oguz could, but not many others can, lead a nation at that age.
--------------------------------------
The weirdest, most disturbing measure of “reason” was when I found a wikipedia site that lists the age that people are allowed to marry in different countries (and states) around the world. Females are almost always “allowed” to marry at younger ages than males. A lot of places have one age for usual cases and another set – again females are younger than males – for cases with parental consent. The youngest allowed in the U.S. is 13 for females, 14 for males, with parental consent “or previous marriage.” That last bit is Utah. Yeah. Yemen, lists 9 with the caveat: “In 1999, the minimum marriage age of fifteen for women, rarely enforced, was abolished; the onset of puberty, interpreted to be at the age of nine, was set as a requirement for consummation of marriage.” Yeah.
Of course, age of consent and age of reason are two totally different things… Right? Of course, in the case of the 9 y/o, who is it that is consenting, really?
-----------------------------------------------
Brain Immaturity Could Explain Teen Crash Rate
Risky Behavior Diminishes At Age 25, NIH Study Finds
By Elizabeth Williamson
Washington Post Staff Writer
Tuesday, February 1, 2005; Page A01
By most physical measures, teenagers should be the world's best drivers. Their muscles are supple, their reflexes quick, their senses at a lifetime peak. Yet car crashes kill more of them than any other cause -- a problem, some researchers believe, that is rooted in the adolescent brain.
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."
Last month, Sen. William C. Mims (R-Loudoun) cited brain development research in proposing a Virginia bill that would ban cell phone use in vehicles by drivers younger than 18. It passed Friday.
In Maryland, Dels. Adrienne A. Mandel and William A. Bronrott said the research could bolster three bills the Montgomery County Democrats submitted to the legislature Friday. The bills would expand training and restrict passenger numbers and cell phone use for certain teenage drivers.
The measures also are supported by crash statistics and a soon-to-be-released study from Temple University, which used a driving-style test to show that young people consistently take greater risks when their friends are watching.
"This goes toward supporting evidence that the judgment of teens further deteriorates with distractions. These crashes are preventable," Mandel said. "I would welcome [researchers'] testimony at our bill hearings."
The research has implications beyond driving: Attorneys cited brain development studies as the U.S. Supreme Court considered whether juvenile offenders should be eligible for the death penalty. The court is expected to reach a decision by midyear.
Critics of brain-imaging research -- and Giedd himself -- emphasize that there is no proven correlation between brain changes and behavior. Giedd, however, said the duration and depth of the study mean "it's time to bring neuroscience to the table" in the teen driving debate.
"We can determine what is the relationship between brain development and driving ability and what we can do to make it better," Giedd said.
At Temple University in Philadelphia, psychology professor and researcher Laurence Steinberg plans a new study: scanning teenagers' brains while they perform a task that simulates driving decisions, in an effort to understand the biological underpinnings of risk-taking among young people.
Giedd intends to pursue similar studies with his subjects, focusing on ways to give young people, and those responsible for them, more tools for beating the odds.
Teenagers are four times as likely as older drivers to be involved in a crash and three times as likely to die in one, according to the Insurance Institute for Highway Safety.
"Right now our first subjects are reaching driving age," Giedd said. "What better application could there be than saving their lives?"
Environmental Impact
Lily and Zoe Ulrich, 15-year-old identical twins from Frederick, have been part of Giedd's study at NIH for two years. When they signed up, they answered questions about their diet, athletics, social habits, peer pressure, language skills and intellectual achievements.
The blond, 5-foot-4 sisters wear glasses, earn straight A's and often finish each other's sentences. They will receive their learner's permits this month. "I'm excited . . . it's really cool," Lily said. "I'm a little more nervous," said Zoe. "We think the same a lot of the time but not always."
Giedd would like to know why.
Sitting in his closet-size office in NIH's sprawling Building 10, he turns to his laptop, where the fruit of 13 years' work appears. It's an eight-second, time-lapse image of the brain, swept by a vivid blue wave symbolizing maturing gray matter. The color engulfs the frontal lobes and ends in "a direct hit," Giedd said, with the dorsal-lateral prefrontal cortex, just behind the brow.
About as thick and wide as a silver dollar, this region distinguishes humans from other animals. From it, scientists believe, come judgments and values, long-term goals, the weighing of risks and consequences -- what parents call wisdom or common sense and what science calls "executive functions."
While society and tradition have placed the point of intellectual maturity, the "age of reason," years earlier, the study -- an international effort led by NIH's Institute of Mental Health and UCLA's Laboratory of Neuro Imaging -- shows it comes at about age 25.
The process is generally completed a year or two earlier in women but varies greatly from person to person. Why that is, Giedd said, "we still don't know."
"We have to find out what matters. Diet? Education, video games? Medicine, parenting, music? Is the biggest factor whether you're a musician or a jock or the amount of sleep you get?"
As important, Giedd said, is the study's finding that the brain matures in a series of fits and starts. While it remains to be proved, he said, this "may be a key to when the brain is most receptive" to learning certain skills, such as driving.
The study, which is ongoing, involves scanning the brains of 2,000 people ages 4 through 26 using magnetic resonance imaging, a radiation-free tool that permits researchers to view the organs of healthy people in minute detail.
Every two years, study participants come to the Bethesda-based National Institute of Mental Health, where they are scanned and interviewed. Half the children are healthy, and half have brain-related disorders. In the next phase, researchers plan to focus almost solely on twins, hoping to expand beyond the 180 pairs participating now, to measure the impact of environmental factors on the maturing brain.
Giedd said he's been bashed by teenagers who said the study suggests they're brain-damaged. On the contrary, he said: "Teenagers' brains are not broken; they're just still under construction."
The pattern probably serves an evolutionary purpose, he said, perhaps preparing youths to leave their families and fend for themselves, without wasting energy worrying about it.
The findings imply that many life choices -- college and career, marriage and military service -- often are made before the brain's decision-making center comes fully online. But for young adults, "dying on a highway is the biggest risk out there," Giedd said. "What if we could predict earlier in life what could happen later?"
A 'Period of Recklessness'
Temple's Steinberg said the NIH/UCLA research supports his theory that teen recklessness is partly the result of a critical gap in time -- starting with the thrill-seeking that comes in puberty and ending when the brain learns to temper such behavior. Since children today reach puberty earlier than previously, about age 13, and the brain's reasoning center doesn't reach maturity until the mid-twenties, Steinberg said, "this period of recklessness has never been as long as it is now."
In a study to be published this year, Temple researcher Margo Gardner and Steinberg illustrated the impact of peer pressure on risk-taking. Volunteers in three age groups -- 13 to 16, 18 to 22 and 24 and older -- were told to bring two friends to the study, which involved an arcade-style driving game.
To "win," participants guided a car through a course as quickly as possible. Periodically, a yellow warning light flashed, and some time later a "wall" popped up. If players hit it, they lost all their "points."
Participants took the test alone and with their friends in the room. Researchers found that those in the two younger groups consistently took more chances with friends present. Those 24 and older behaved equally cautiously, regardless of whether friends were watching.
The results help show why teenagers are more likely to drink, take drugs or commit crimes in groups, he said. They're also reflected in auto crash statistics.
According to the Arlington-based Insurance Institute for Highway Safety, the chances of a crash by a 16- or 17-year-old driver are doubled with two peers in the vehicle and quadrupled with three or more. "Every passenger you add increases the risk," said Alan Williams, chief scientist at the institute. The brain and behavior studies, he said, "certainly tie in with what we know."
After a spate of teen driving deaths across the Washington region in the fall, Maryland is attempting to join Virginia and the District in limiting the number of unrelated passengers in cars with young drivers. In addition to cell phone restrictions that the Maryland and Virginia legislatures are considering, Maryland Gov. Robert L. Ehrlich Jr. (R) is backing a measure that would revoke the licenses of convicted drunk drivers under age 21, for as long as five years.
Steinberg said he agrees with such approaches. "We have to limit the harm adolescents [encounter], rather than to try and change them."
The best way to do that, he added, "is by passing laws."
I have culled evidence from various sites. Enjoy!
Wisdom teeth, also known as third molars, are the last teeth to erupt in your mouth. This generally occurs between the ages of 17 and 25, a time of life that has been called the "Age of Wisdom." Via The American Association of Oral and Maxillofacial Surgeons.
According to the Catholic Church, as quoted from the Catholic Encyclopedia, the age of reason is defined as follows:
The name given to that period of human life at which persons are deemed to begin to be morally responsible. This, as a rule, happens at the age of seven, or thereabouts, though the use of reason requisite for moral discernment may come before, or may be delayed until notably after, that time. At this age Christians come under the operation of ecclesiastical laws, such as the precept of assistance at Mass on Sundays and holy days, abstinence from meat on certain days, and annual confessions, should they have incurred mortal sin. The obligation of Easter Communion literally understood applies to all who have reached "the years of discretion"; but according to the practical interpretation of the Church it is not regarded as binding children just as soon as they are seven years old. At the age of reason a person is juridically considered eligible to act as witness to a marriage, as sponsor at baptism or confirmation, and as a party to the formal contract of betrothal; at this age one is considered capable of receiving extreme unction, of being promoted to first tonsure and minor orders, of being the incumbent of a simple benefice (beneficium simplex) if the founder of it should have so provided; and, lastly, is held liable to ecclesiastical censures. In the present discipline, however, persons do not incur these penalties until they reach the age of puberty, unless explicitly included in the decree imposing them. The only censure surely applicable to persons of this age is for the violation of the clausura of nuns, while that for the maltreatment, suadente diabolo, of clerics is probably so.
I did end up finding the source of my use of 25 years old as the Age of Reason, it is an NIH study described in this Washington Post article about brain immaturity and its relation to vehicular crashes. I’ve quoted bits and pieces below, the full article is at the end of the post:
By most physical measures, teenagers should be the world's best drivers. Their muscles are supple, their reflexes quick, their senses at a lifetime peak. Yet car crashes kill more of them than any other cause -- a problem, some researchers believe, that is rooted in the adolescent brain.
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.
About as thick and wide as a silver dollar, the region (the dorsal-lateral prefrontal cortex, just behind the brow) distinguishes humans from other animals. From it, scientists believe, come judgments and values, long-term goals, the weighing of risks and consequences -- what parents call wisdom or common sense and what science calls "executive functions."
While society and tradition have placed the point of intellectual maturity, the "age of reason," years earlier, the study -- an international effort led by NIH's Institute of Mental Health and UCLA's Laboratory of Neuro Imaging -- shows it comes at about age 25.
The process is generally completed a year or two earlier in women but varies greatly from person to person. Why that is, Giedd said, "we still don't know."
The pattern probably serves an evolutionary purpose, he said, perhaps preparing youths to leave their families and fend for themselves, without wasting energy worrying about it.
The findings imply that many life choices -- college and career, marriage and military service -- often are made before the brain's decision-making center comes fully online.
Temple's Steinberg said the NIH/UCLA research supports his theory that teen recklessness is partly the result of a critical gap in time -- starting with the thrill-seeking that comes in puberty and ending when the brain learns to temper such behavior. Since children today reach puberty earlier than previously, about age 13, and the brain's reasoning center doesn't reach maturity until the mid-twenties, Steinberg said, "this period of recklessness has never been as long as it is now."
Apparently, rental car companies agree with the 25 year old “Age of Reason” since they don’t rent to anyone under that age, and if they do, you’d have to be at least 21 and pay a sometimes hefty surcharge. Because of the high accident rate associated with drivers under 25 (and the severity of those incidents), "car-rental companies don't think it's worth the risk to rent to this age group," says William Maloney, chief operating officer for the American Society of Travel Agents.
An interesting anecdotal story found here about the stages we pass through as described by SAPARMURAT TURKMENBASHY THE GREAT (1940-2006):
In August 2002, the president of Turkmenistan, Saparmurat Niyazov, who's generally referred to by your average Turkman as "Turkmenbashi the Great," decreed that the country would change its perspective on how its citizens view aging. It's interesting to compare this worldview with our Euro-American take on time.
Turkmenbashi the Great, whom I will refer to as Niyazov for short, has defined and divided the Ages of Man into nine segments, each of which is a dozen or so years long. This lifetime calendar has stretched the potential life span to an optimistic 109 years, although statistics show a peculiar tendency of the average Turkman to come up about 49 years short of that goal.
The president declares that "childhood" shall last for 13 years from birth. That's pretty much what we in the West say, too.
Then come the years 14-25, which Niyazov categorizes as "adolescence." Here we begin to diverge in perspective. While there's not much disagreement about the initial teen year, thanks to such enlightened and progressive industrial world advancements as food laced with growth hormones and a popular media which uses sex to sell everything from soup to - er - nuts, our adolescence tends to end at, say, age 15. Then you're an adult, if not legally then certainly physically and attitudinally.
After adolescence comes a dozen years of "youth," terminating at 37. I can't think of anyone I know in that age bracket who would care to disagree with that definition, although some of their cardiologists might.
Until age 49, one enjoys the "Age of Maturity." Again, it's hard to disagree with the definition, although there is the bizarre Western tendency toward immaturity in the later stages of this phase. We call it "mid-life crisis," but obviously we may have to adjust that as acceptance of the Niyazov Numbers becomes more widespread.
An amusing pun comes forth in the next phase, the "Age of the Prophet," which lasts until one's 62nd year. Again, this closely follows our Western outlook, with only a spelling change to make it "Profit" instead.
Then the "Age of Inspiration" kicks in. This also is encouraging, especially for Turkmen, since this is greater than their actual expected life span. Nothing like a little inspiration to keep you going.
Starting at 73 comes the age of the "White Bearded Elder." Providing one still has hair, this time of one's life could be quite ego flattering.
And here's good news for the federal pension plan: under the Turkmen calendar "Old Age" doesn't kick in until age 85. This, of course, conflicts by two decades with our own definition. But you don't need to be an actuary to see how our country could benefit financially by delaying old-age benefit payments until people reached this new, imaginative chronological benchmark.
Next, at 97, Turkmenbashi the Great pays homage to Oguz Khan, an ancient figure who led his country presumably up until age 109. This will be, Niyazov declares, a person's "Age of Oguz Khan."Perhaps Oguz could, but not many others can, lead a nation at that age.
--------------------------------------
The weirdest, most disturbing measure of “reason” was when I found a wikipedia site that lists the age that people are allowed to marry in different countries (and states) around the world. Females are almost always “allowed” to marry at younger ages than males. A lot of places have one age for usual cases and another set – again females are younger than males – for cases with parental consent. The youngest allowed in the U.S. is 13 for females, 14 for males, with parental consent “or previous marriage.” That last bit is Utah. Yeah. Yemen, lists 9 with the caveat: “In 1999, the minimum marriage age of fifteen for women, rarely enforced, was abolished; the onset of puberty, interpreted to be at the age of nine, was set as a requirement for consummation of marriage.” Yeah.
Of course, age of consent and age of reason are two totally different things… Right? Of course, in the case of the 9 y/o, who is it that is consenting, really?
-----------------------------------------------
Brain Immaturity Could Explain Teen Crash Rate
Risky Behavior Diminishes At Age 25, NIH Study Finds
By Elizabeth Williamson
Washington Post Staff Writer
Tuesday, February 1, 2005; Page A01
By most physical measures, teenagers should be the world's best drivers. Their muscles are supple, their reflexes quick, their senses at a lifetime peak. Yet car crashes kill more of them than any other cause -- a problem, some researchers believe, that is rooted in the adolescent brain.
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."
Last month, Sen. William C. Mims (R-Loudoun) cited brain development research in proposing a Virginia bill that would ban cell phone use in vehicles by drivers younger than 18. It passed Friday.
In Maryland, Dels. Adrienne A. Mandel and William A. Bronrott said the research could bolster three bills the Montgomery County Democrats submitted to the legislature Friday. The bills would expand training and restrict passenger numbers and cell phone use for certain teenage drivers.
The measures also are supported by crash statistics and a soon-to-be-released study from Temple University, which used a driving-style test to show that young people consistently take greater risks when their friends are watching.
"This goes toward supporting evidence that the judgment of teens further deteriorates with distractions. These crashes are preventable," Mandel said. "I would welcome [researchers'] testimony at our bill hearings."
The research has implications beyond driving: Attorneys cited brain development studies as the U.S. Supreme Court considered whether juvenile offenders should be eligible for the death penalty. The court is expected to reach a decision by midyear.
Critics of brain-imaging research -- and Giedd himself -- emphasize that there is no proven correlation between brain changes and behavior. Giedd, however, said the duration and depth of the study mean "it's time to bring neuroscience to the table" in the teen driving debate.
"We can determine what is the relationship between brain development and driving ability and what we can do to make it better," Giedd said.
At Temple University in Philadelphia, psychology professor and researcher Laurence Steinberg plans a new study: scanning teenagers' brains while they perform a task that simulates driving decisions, in an effort to understand the biological underpinnings of risk-taking among young people.
Giedd intends to pursue similar studies with his subjects, focusing on ways to give young people, and those responsible for them, more tools for beating the odds.
Teenagers are four times as likely as older drivers to be involved in a crash and three times as likely to die in one, according to the Insurance Institute for Highway Safety.
"Right now our first subjects are reaching driving age," Giedd said. "What better application could there be than saving their lives?"
Environmental Impact
Lily and Zoe Ulrich, 15-year-old identical twins from Frederick, have been part of Giedd's study at NIH for two years. When they signed up, they answered questions about their diet, athletics, social habits, peer pressure, language skills and intellectual achievements.
The blond, 5-foot-4 sisters wear glasses, earn straight A's and often finish each other's sentences. They will receive their learner's permits this month. "I'm excited . . . it's really cool," Lily said. "I'm a little more nervous," said Zoe. "We think the same a lot of the time but not always."
Giedd would like to know why.
Sitting in his closet-size office in NIH's sprawling Building 10, he turns to his laptop, where the fruit of 13 years' work appears. It's an eight-second, time-lapse image of the brain, swept by a vivid blue wave symbolizing maturing gray matter. The color engulfs the frontal lobes and ends in "a direct hit," Giedd said, with the dorsal-lateral prefrontal cortex, just behind the brow.
About as thick and wide as a silver dollar, this region distinguishes humans from other animals. From it, scientists believe, come judgments and values, long-term goals, the weighing of risks and consequences -- what parents call wisdom or common sense and what science calls "executive functions."
While society and tradition have placed the point of intellectual maturity, the "age of reason," years earlier, the study -- an international effort led by NIH's Institute of Mental Health and UCLA's Laboratory of Neuro Imaging -- shows it comes at about age 25.
The process is generally completed a year or two earlier in women but varies greatly from person to person. Why that is, Giedd said, "we still don't know."
"We have to find out what matters. Diet? Education, video games? Medicine, parenting, music? Is the biggest factor whether you're a musician or a jock or the amount of sleep you get?"
As important, Giedd said, is the study's finding that the brain matures in a series of fits and starts. While it remains to be proved, he said, this "may be a key to when the brain is most receptive" to learning certain skills, such as driving.
The study, which is ongoing, involves scanning the brains of 2,000 people ages 4 through 26 using magnetic resonance imaging, a radiation-free tool that permits researchers to view the organs of healthy people in minute detail.
Every two years, study participants come to the Bethesda-based National Institute of Mental Health, where they are scanned and interviewed. Half the children are healthy, and half have brain-related disorders. In the next phase, researchers plan to focus almost solely on twins, hoping to expand beyond the 180 pairs participating now, to measure the impact of environmental factors on the maturing brain.
Giedd said he's been bashed by teenagers who said the study suggests they're brain-damaged. On the contrary, he said: "Teenagers' brains are not broken; they're just still under construction."
The pattern probably serves an evolutionary purpose, he said, perhaps preparing youths to leave their families and fend for themselves, without wasting energy worrying about it.
The findings imply that many life choices -- college and career, marriage and military service -- often are made before the brain's decision-making center comes fully online. But for young adults, "dying on a highway is the biggest risk out there," Giedd said. "What if we could predict earlier in life what could happen later?"
A 'Period of Recklessness'
Temple's Steinberg said the NIH/UCLA research supports his theory that teen recklessness is partly the result of a critical gap in time -- starting with the thrill-seeking that comes in puberty and ending when the brain learns to temper such behavior. Since children today reach puberty earlier than previously, about age 13, and the brain's reasoning center doesn't reach maturity until the mid-twenties, Steinberg said, "this period of recklessness has never been as long as it is now."
In a study to be published this year, Temple researcher Margo Gardner and Steinberg illustrated the impact of peer pressure on risk-taking. Volunteers in three age groups -- 13 to 16, 18 to 22 and 24 and older -- were told to bring two friends to the study, which involved an arcade-style driving game.
To "win," participants guided a car through a course as quickly as possible. Periodically, a yellow warning light flashed, and some time later a "wall" popped up. If players hit it, they lost all their "points."
Participants took the test alone and with their friends in the room. Researchers found that those in the two younger groups consistently took more chances with friends present. Those 24 and older behaved equally cautiously, regardless of whether friends were watching.
The results help show why teenagers are more likely to drink, take drugs or commit crimes in groups, he said. They're also reflected in auto crash statistics.
According to the Arlington-based Insurance Institute for Highway Safety, the chances of a crash by a 16- or 17-year-old driver are doubled with two peers in the vehicle and quadrupled with three or more. "Every passenger you add increases the risk," said Alan Williams, chief scientist at the institute. The brain and behavior studies, he said, "certainly tie in with what we know."
After a spate of teen driving deaths across the Washington region in the fall, Maryland is attempting to join Virginia and the District in limiting the number of unrelated passengers in cars with young drivers. In addition to cell phone restrictions that the Maryland and Virginia legislatures are considering, Maryland Gov. Robert L. Ehrlich Jr. (R) is backing a measure that would revoke the licenses of convicted drunk drivers under age 21, for as long as five years.
Steinberg said he agrees with such approaches. "We have to limit the harm adolescents [encounter], rather than to try and change them."
The best way to do that, he added, "is by passing laws."
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