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Aided by brain imaging advances, scientists are looking for evidence that compulsive nondrug behaviors lead to long-term changes in reward circuitry
People toss around the term "addiction" to describe someone's relationship to a job, a boyfriend, or a computer. But scientists have traditionally confined their use of the term to substances-namely alcohol and other drugs -that clearly foster physical dependence in the user.
That's changing, however. New knowledge about the brain's reward system, much gained by superrefined brain scan technology, suggests that as far as the brain is concerned, a reward's a reward, regardless of whether it comes from a chemical or an experience. And where there's a reward, there's the risk of the vulnerable brain getting trapped in a compulsion.
"Over the past 6 months, more and more people have been thinking that, contrary to earlier views, there is commonality between substance addictions and other compulsions," says Alan Leshner, head of the National Institute on Drug Abuse (NIDA) and incoming executive officer of the American Association for the Advancement of Science, publisher of Science.
Just where to draw the line is not yet clear. The unsettled state of definitions is reflected in psychiatry's bible, the Diagnostic and Statistical Manual IV. Addictions, obsessions, and compulsions-all related to loss of voluntary control and getting trapped in repetitious, selfdefeating behavior-are scattered around under "substance-related disorders," "eating disorders," "sexual and gender identity disorders," "anxiety disorders," and "impulse-- control disorders not elsewhere classified." In that last grab-bag are compulsive gambling, kleptomania, fire-setting, hair-pulling, and "intermittent explosive disorder."
Addiction used to be defined as dependence on a drug as evidenced by craving, increased tolerance, and withdrawal. But even some seemingly classical addictions don't follow that pattern. Cocaine, for example, is highly addictive but causes little withdrawal. And a person who gets hooked on morphine while in the hospital may stop taking the drug without developing an obsession with it.
Now many researchers are moving toward a definition of addiction based more on behavior, and they are starting to look at whether brain activity and biochemistry are affected the same way in "behavioral" addictions as they are by substance abuse. One who endorses this perspective is psychologist Howard Shaffer, who heads the Division on Addictions at Harvard. "I had great...