Researchers say that drugs may create "extreme" memories by overstimulating the brain's dopamine system, warping an ancient learning system to create addictions.

Harvard University neuroscientist Steven E. Hyman said that dopamine is deeply involved in human survival skills, helping to create memories of essentials like food and water sources. The chemical says to the brain, "This is very important; let's remember exactly how we did this," said Hyman.

When drugs cause an overabundance of dopamine, he said, it may cause the brain to "overlearn," creating a memory of drugs as "good." These memories and associations about drugs can remain strong for a long time, perhaps a lifetime. Hyman spelled out some his theories in an article entitled "Addiction: A Disease of Learning and Memory" in the American Journal of Psychiatry last year, and discussed them further at a recent forum held at the Massachusetts Institute of Technology.

The National Institute on Drug Abuse also is researching the "extreme memory" and "pathological learning" theories, with animal studies aimed at trying to replace unwanted drug memories with new memories to prevent relapse. NIDA director Nora Volkow said that medications that alter memory could "erase the memory of the pleasure associated with the drug." One such medication being tested is D-Cycloserine.

"We often think of treatment as quitting and staying quit," said Shelly F. Greenfield, associate clinical director of the Alcohol and Drug Abuse Treatment Program at McLean Hospital. "Most people, I think, would agree that the quitting part is easier than the staying quit."