A part of the brain involved in both drug craving and judgment appears to be smaller in cocaine addicts than in healthy people, researchers have found.

Analyzing brain scans from 27 people addicted to cocaine and 27 healthy adults of the same age, the researchers found that in the drug abusers, a brain structure called the amygdala was smaller than normal.

Exactly what the finding means is not yet clear, but several pieces of evidence suggest that reduced volume in the amygdala may predispose a person to cocaine addiction, the study’s senior author told AMN Health.

The amygdala is a collection of nuclei in the brain involved in the processing of emotion. Brain-imaging studies have tied drug craving to activity in the amygdala, and recent research has also suggested that the brain structure aids in sizing up the potential negative outcomes of an action.

It’s such judgment that people with drug addiction typically lack, Dr. Hans C. Breiter of Massachusetts General Hospital in Boston noted in an interview with Reuters Health.

His team’s study, published in the November 18th issue of the journal Neuron, cannot answer the question of whether smaller amygdala volume is a contributor to or consequence of cocaine addiction, Breiter said.

However, he pointed to evidence that supports a causal role. For example, amygdala volume did not correspond with the level of a person’s drug abuse; cocaine users in the study had abused the drug for anywhere from one to 27 years, yet had similar reductions in amygdala size.

In addition, Breiter explained, during normal development, the right-hemisphere amygdala becomes larger than the left. However, in these cocaine addicts, he said, “there was a loss of this asymmetry.”

It seems unlikely, the researcher noted, that drug abuse would have affected only one side of the brain in these individuals. Instead, he said, such a loss of asymmetry in the amygdala would seem to have genetic underpinnings.

But if a reduction in amygdala volume is involved in cocaine addiction, the implications would be great regardless of whether it’s a cause or effect, according to Breiter.

If even short-term cocaine abuse can cause such “dramatic” degenerative change in the brain, he said, that would highlight a prime danger of the drug.

On the other hand, if smaller amygdala volume raises a person’s vulnerability to cocaine addiction, then it offers a potential way to reveal that risk. According to Breiter, it might become possible for people with a family history of any forms of addiction to get a brain scan of the amygdala to see if they have this structural predisposition.

The fact that the amygdala appears to be involved in judging the potential pitfalls of an action may help explain how an abnormality in its structure could make a person susceptible to cocaine addiction, according to Breiter.

However, there is also the amygdala’s role in drug craving. An interesting finding, Breiter noted, was that “the smaller the amygdala was, the more they craved for cocaine.”

Whether the findings are unique to cocaine is not yet clear. The study is part of a larger project by Breiter and his colleagues that is using advanced brain imaging to find potentially inherited “markers” in the brain - such as differences in structure or nerve activity - that are associated with addiction and mood disorders such as depression.

SOURCE: Neuron, November 18, 2004.