BOSTON, MA — New research on the brain is showing that addiction is a matter of memories, and recovery is a slow process in which the influence of those memories is diminished, reports the January 2007 issue of the Harvard Mental Health Letter.

Studies have shown that addictive drugs stimulate a reward circuit in the brain. The circuit provides incentives for action by registering the value of important experiences. Rewarding experiences trigger the release of the brain chemical dopamine, telling the brain "do it again." What makes permanent recovery difficult is drug-induced change that creates lasting memories linking the drug to a pleasurable reward.

Recent research shows that addiction involves many of the same brain circuits that govern learning and memory. Long-term memories are formed by the activity of brain substances called transcription factors. All perceived rewards, including drugs, increase the concentration of transcription factors. So repeatedly taking drugs can change the brain cells and make the memory of the pleasurable effects very strong. Even after transcription factor levels return to normal, addicts may remain hypersensitive to the drug and the cues that predict its presence. This can heighten the risk of relapse in addicts long after they stop taking the drug.

Knowing more about how addiction works in the brain has not yet given us any strikingly effective new treatments, but it has suggested new possibilities while providing a better understanding of how the available treatments work. "The hardest job will be finding substances that lower the risk of addiction but do not interfere with responses to natural rewards," says Dr. Michael Miller, editor in chief of the Harvard Mental Health Letter. So far there is little evidence that any one type of therapy works better for addiction than another.