Scientists using powerful scanners have documented nicotine triggering dramatic bursts of activity in certain brain areas - but only in people prone to anger and aggression, not more cheerful, relaxed types.
Researchers made the discovery when studying people wearing nicotine patches. Intriguingly, the nicotine jazzed up the brains of not just smokers who are aggressive, but of nonsmokers, too - and at very low doses.
It's the first biological evidence that people with certain personality traits are more likely to get hooked on smoking if they ever experiment with cigarettes.
And it may help explain why it's so much easier for some people to kick the addiction than others, says psychiatrist Steven Potkin of the University of California, Irvine, who led the study.
It's almost, he says, as if some people are born to smoke.
Other scientists won't make that leap, noting that it's not clear how much of a person's personality is genetic and how much stems from childhood environments. Smoking habits, too, can depend greatly on whether people grew up surrounded by smokers and the social and cultural conditions under which they try to quit.
Still, "we're looking for the variety of things that could make people likely to smoke, and this could be one of them," says William Corrigall of the National Institute on Drug Abuse.
It also has important implications for teenagers. Adolescents are prone to periods of aggression before parts of the brain that control impulse and behavior finish forming - and smokers almost universally pick up the habit as teens.
If doctors could predict who's most at risk of getting hooked after their first few cigarettes, perhaps they could better target those people with smoking prevention programs.
Previous surveys had suggested that Type A personalities are more likely to be big smokers, especially when nervous or irritated. Also, some scientists have put smokers into brain scanners while infusing them with nicotine, to see what brain areas the drug targets.
But Potkin's study took the crucial step of adding nonsmokers to the mix. And he asked 86 people to do various tests - such as computer games that showed who were the sore losers - while a PET scanner monitored their brain activity before and after receiving low- or high-dose nicotine patches or a sham patch.
"No one has looked at nicotine in this way," says Kenneth Perkins, a psychiatry professor at the University of Pittsburgh who also is studying predictive traits of smoking.
The PET scans showed no brain effects of nicotine on people whose personalities were more relaxed and cheerful.
But in people rated as having more hostile tendencies - easier to anger, more impatient or irritable - nicotine triggered dramatic changes in activity in brain regions important for controlling emotion and social response.
For some people, nicotine increased energy metabolism, for others, it decreased, depending on dose.
But despite the common assumption that nicotine can be calming, actually "nicotine made them even more aggressive," Potkin says. "They may smoke to feel better, but they don't feel better."
That's a curious finding, Perkins says, but it may be because the study used different doses. Low nicotine doses sometimes stimulate brain activity while high doses suppress other activity.
The next step: Seeing how the brain reacts when people smoke instead of having carefully controlled doses of nicotine administered via a patch. For that study, Potkin can't induce nonsmokers to start smoking, so he'll compare regular smokers to people who puff a few cigarettes every so often.
By Lauran Neergaard