Who's an Addict?

med0402addiction_A6.jpg WHAT BRAIN SCANS REVEAL

Clockwise, from top left: Normal brain, brain of an obese person, brain of an alcoholic, brain of a cocaine user.

The brightly colored areas in these images mark the nucleus accumbens, the brain's reward center. Red indicates a high number of receptors for dopamine, a brain chemical that transmits sensations of pleasure; yellow and green indicate fewer receptors. People short on dopamine receptors have difficulty feeling joy. Many scientists have been surprised by recent studies revealing that the biochemistry of classic addictions, such as alcoholism and drug abuse, is strikingly similar to that of compulsive activities, including gambling and overeating.

It's Martin Luther King Jr.'s birthday, and Hans Breiter, director of the Motivation and Emotion Neuroscience Center at Massachusetts General Hospital, has the day off. Sort of. He's sitting in his home art studio, gluing together a statue that broke soon after his 9-year-old son made it. Meanwhile, with his cellphone kinked against his neck, Breiter is fielding call after call, discussing the intricacies of neuroscience with people he couldn't squeeze into his hectic weekday schedule.


Breiter's life is a blur of family and research; he jokes that skimping on sleep is the only way he fits it all in. But ask him if he's a work addict and he becomes stone serious. "That stuff's controversial," he says, "very controversial."


The question of whether a behavior-like work, sex, exercise, or gambling-can be characterized as addictive in the same way drugs are is at the heart of an intense debate among neuroscientists and psychiatrists.


On one side are researchers like Breiter, who has recently published some of the most tangible evidence
yet that certain pathological human behaviors travel the same biological pathways as addictive drugs. Using brain-imaging technology, Breiter demonstrated that gamblers at slot machines show increased blood flow
in the same brain areas where cocaine produces a surge in dopamine-the transmitter that carries neural messages relating to pleasure and pain.


Eric Nestler, professor of psychiatry at the University of Texas Southwestern Medical Center, obtained results that point to another pathway shared by addictive drugs and some pathological behaviors. In a series of experiments on rodents, Nestler showed that the same proteins that regulate genes involved with drug addiction seemed to escalate tendencies toward pathological exercise. "These animals sometimes run 20 miles a day in a little wheel, and show the same changes in brain reward pathways that we've seen in drug addicts," he says. In fact, by manipulating these proteins, Nestler was able to stop the animals' apparent exercise compulsion.


Other investigators have used both animal and human studies to show that cocaine addicts and overeaters experience similar dopamine responses. And there is also evidence that medications for treating drug addictions, such as naltrexone for narcotics, can diminish the urge for gambling and shoplifting.


Still, many researchers are not so quick to buy into the conclusion that
so-called addictive behaviors and drug addiction should be classified together. "We can learn a lot by looking at the ways addictions are similar to behaviors, and we can learn a lot by looking at the ways they're different," says Roy Wise, chief of the behavioral neuroscience branch of the National Institute on Drug Abuse. "But we don't know if any of these things happening in the brain are causes of addiction, consequences of addiction, or predisposing factors for addiction."