Washington ? Call it the science of peer pressure. When teenagers fail to just say no to drugs, Dr. Nora Volkow blames their brains, not their willpower – they lack links between some crucial brain regions that won’t fully form until they’re adults.

Age matters a lot when it comes to drug abuse. It’s an evolving view of addiction that Volkow brings as head of the government’s National Institute on Drug Abuse. And it’s a career born of a tragic family history – she’s the great-granddaughter of assassinated Russian revolutionary Leon Trotsky – that sparked an urge to help others.

“I do believe we all have a responsibility with our lives,” Volkow says with passion. “It’s just an extraordinary miracle that we exist, as a person with our unique characteristics.”

Unique is a word many use to describe Volkow, 49, who grew up in the Mexico City house where her famous ancestor was killed, and moved to the United States in her 20s to pioneer research peering inside living people’s brains to trace the effects of drugs.

She first achieved acclaim by discovering that cocaine was neurotoxic, a radical notion in the early 1980s. Since then, she has systematically probed alcohol, nicotine, heroin, methamphetamine, even overeating – obesity, she recently reported, shares many compulsive traits with drug abuse – to uncover the brain circuitry that underpins addiction.

Now, three years into a stint directing the government’s $1 billion anti-drug research program, Volkow is channeling new energy into determining exactly how the brains of addicts and those who never get hooked differ – so scientists can develop better ways to prevent and treat drug abuse.

“What is it that makes a person more vulnerable to take drugs or not?” she asks.

It’s a far more complex view of addiction than urging people to just say no, says Joanna Fowler, a chemist at the Brookhaven National Laboratory who has collaborated with Volkow for more than two decades.

Dr. Nora Volkow, head of the National Institute on Drug Abuse is seen in her office in Rockville, Md., Wednesday, March 22, 2006. Volkow is also an artist, one of her painting behind her shows blood flowing thorough an MRI scan of the body.

“Now we have Nora’s picture rather than a picture of fried eggs,” Fowler says, referring to an old government anti-drug campaign that compared a brain on drugs to a sizzling egg. “We can go beyond that knee-jerk picture of a brain to a real brain.”

Teens are particularly vulnerable to addiction because their brains don’t finish forming until the early 20s. The frontal cortex, among the last regions to mature, is where the brain’s cognitive or reasoning side creates connections with emotion-related regions.

So, put teens in an emotionally charged situation – say, surrounded by friends egging them on – and their ability “to stand up and say ‘I’m not going to do it’ is much harder than (for) an adult,” Volkow explains.

Also, teens are more willing to take risks, also because of weak links between the “why-not” side of the brain and the “remember the consequences” side.

In fact, Volkow fears anti-drug programs that attempt to scare teens may inadvertently spur drug experimentation.

“It is that notion of ‘I dare you,'” she says. “It may be appealing to an adolescent because they are seeking for danger in many instances.”

Volkow’s own research shows a promising avenue: Drugs essentially hijack a brain chemical called dopamine that’s involved with sensing pleasure, until eventually abusers can no longer sense pleasure from anything but a high. Social acceptance boosts dopamine, so something as simple as group therapy may help fight drug relapses.

“One of the most powerful things that makes us feel good is when someone we admire, appreciate, for example, values us,” Volkow explains.