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Published in Neuron, researchers comparing the brains of cocaine addicts and normal individuals have found that the addicts show a significant reduction in the size of the amygdala.  By evaluating MRI scans of 27 cocaine addicts and a matched group of non-addicts, the scientists from Harvard Medical School determined the volume of the amygdala in the subjects. The cocaine addicts had amygdala that were an average of 13% smaller on the left side of the brain and a 23% smaller structure on the right side. To make sure that the amygdala was uniquely affected, they also compared the size of a neighboring structure, the hippocampus. They found no significant differences between addicts and controls in the volume of that structure.
Interestingly, the volume of the amygdala in the addicts did not correlate with measures of anxiety or depression, cocaine use, or age at which cocaine use began. In addition, it was also observed that the addicts' brains, compared to normal subjects, showed a loss of "laterality, in which the amygdala in the two sides of the brain was normally approximately equal in volume.
The researchers also noted that the smaller amygdala volumes in the addicts were different than in bipolar illness and Alzheimer's disease, in which both the hippocampus and amygdala can show a loss in volume. There are a number of studies indicating that the amygdala is involved in assessing the rewards or aversive aspects of goals, such as expecting negative outcomes of a course of action. According to this study, this deficit underscores the fact that cocaine-dependent subjects have significant difficulty identifying the potential negative outcomes of their behavior or acknowledging the impact of their behavior.
In a number of animal studies, amygdala changes represent changes in the brain or damage resulting from drug use. Alternatively, the observed amygdala abnormalities could be a developmental condition that predisposes subjects to cocaine abuse or addiction. Additional research is needed and these researchers plan on conducting family-based studies to evaluate if the decreased amygdala volume in cocaine addicts represents a brain-based phenotypic marker for illness that could facilitate genetic studies aimed at discovering the genes that modify the risk for addiction.
PubMed citation
Even Modest Cocaine Use May Cause Brain Changes That Could Contribute to Addiction
(NIDA report)
Cocaine and the Changing Brain
10:31:58 PM 
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