Predicting Addiction

These days, it seems everyone from our parents to our presidents has a confession related to "experimentation" with drugs. But relatively few people who try drugs—only about 1 in 7, according to national surveys—actually become addicted. Thanks to new imaging devices and sophisticated computer tests, scientists hope to have techniques within the next few years that will help individuals determine if they are at high risk of addiction, or of relapse if they are trying to quit.

"Some people progress to dependence and addiction, and some people can exercise controlled drug use, which we generally don't talk about very much," said neuroscientist Steven Grant of the National Institute on Drug Abuse (NIDA). "There is a whole hidden strata of people who do not progress to addiction even with illicit drugs."

"People differ in how quickly and how irreversibly drugs become a habit versus just something that gives them pleasure," agrees Martin Paulus, a psychiatrist at the University of California.

A person's risk of addiction increases with the frequency of use. The greater the quantity, the faster the ride to dependence. But why do some people stop using before addiction sets in, or use drugs only occasionally?

A person's home and community life contribute, but studies show that an individual's genetic makeup accounts for 40 percent to 60 percent of his or her vulnerability to addiction. So researchers are taking a close look at brain activity, to see how genetic differences may be playing out.

How badly do you want it?

NIDA defines addiction as "compulsive drug seeking and use, despite harmful consequences." What's driving that compulsion is a powerful craving for the drug, yet people differ greatly in the strength of their cravings, says Grant.

"Nobody has quite figured out what these individual differences are due to ... it has always been a mystery," he says. "But we are beginning to get some clues."

One of those clues comes from studies on the effects of varying levels in the brain of dopamine, the brain's bearer of good feelings. Dopamine, along with the many neurons and receptors that enable it to strut around the brain, reward us with sensational sensations, such as for experiencing good sex and eating good food. But give the brain drugs, and eventually they hijack this vulnerable reward system.

Imaging the differences

Neuroscientist Teri Franklin and her colleagues used an imaging technique to watch how the reward centers of 19 smokers, who want to quit but haven't yet, responded to two brief movies. One featured people talking and looking happy, and the other showed smokers talking about and smoking cigarettes.

The smoking movie is so seductive it even "makes people who don't smoke want a cigarette," said Franklin, of the Addiction Treatment Research Center at the University of Pennsylvania.

Franklin screened all of the study participants for genetic variations that may influence their levels of dopamine in the brain. About half of the 19 smokers had a common genetic variation that may cause the dopamine that is released in response to cues—such as a movie of someone smoking—to linger longer in certain regions of the brain. Their brains reacted strongly to the movie, showing a lot of activity in the reward-related regions. However, how the smokers ranked the intensity of their cravings didn't match up with what was going on in their brain, the team reported in the online version of Neuropsychopharmacology in August.

Franklin thinks that this group of  study participants' brains may respond very actively to a lot of different types of tempting cues. But because they aren't aware of how their brain is "feeling," and therefore don't know to avoid such cues, "they have a greater risk—vulnerability—to get addicted," Franklin said. However, these are preliminary findings that need to be further investigated, she noted.

In the other study participants, the smoking movie triggered less brain activity, compared to the movie of people just talking. However, their ratings of their cravings while watching the movie matched up with how their brain reacted, said Franklin. These individuals may be less vulnerable to relapse, for example, when they actually do quit smoking.