The teenage brain is like a car with a good accelerator but a weak brake. With powerful impulses under poor control, the likely result is a crash.

And, perhaps, a crime.

Laurence Steinberg, a Temple University psychology professor, helped draft an American Psychological Association brief for a 2005 case in which the US Supreme Court outlawed the death penalty for crimes committed before age 18.

That ruling relies on the most recent research on the adolescent brain, which indicates the juvenile brain is still maturing in the teen years and reasoning and judgment are developing well into the early to mid 20s. It is often cited as state lawmakers consider scaling back punitive juvenile justice laws passed during the 1990s.

"As any parent knows," wrote Justice Anthony Kennedy for the 5-4 majority, youths are more likely to show "a lack of maturity and an underdeveloped sense of responsibility" than adults. "... These qualities often result in impetuous and ill-considered actions and decisions."

He also noted that "juveniles are more vulnerable or susceptible to negative influences and outside pressures, including peer pressure," causing them to have less control.

Some child advocates have pointed to the Supreme Court decision and the research as evidence that teens - even those accused of serious crimes - should not be regarded in the same way as adults in the criminal justice system.

Dr David Fassler, a psychiatry professor at the University of Vermont College of Medicine who has testified before legislative committees on brain development, says the research doesn't absolve teens but offers some explanation for their behavior.

"It doesn't mean adolescents can't make a rational decision or appreciate the difference between right and wrong," he said.

"It does mean, particularly when confronted with stressful or emotional decisions, they are more likely to act impulsively, on instinct, without fully understanding or analyzing the consequences of their actions."

(Agencies via China Daily December 3, 2007)