Hans Breiter and his colleagues wrote that the finding could not distinguish conclusively whether a smaller amygdala might predispose people to addiction or whether it was a result of the addiction. However, they said that their results indicate that the condition might pre-exist addiction. They suggested that family-based studies and longitudinal studies of cocaine addicts would reveal whether a reduced amygdala volume might underlie a vulnerability to addiction.
In their study, the researchers scanned the brains of 27 cocaine addicts and a matched group of nonaddicts. The scans were done using magnetic resonance imaging, a widely used technique in which harmless magnetic fields and radio signals are used to create three-dimensional images of the brain. The researchers used data from the brain scans to determine the volume of the amygdalas in the subjects.
The researchers found that the amygdalas of the cocaine addicts were significantly smaller than the control subjects--with an average 13% smaller amygdala 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, the researchers also compared the size of a neighboring structure, the hippocampus, which plays a role in learning reward and aversion. They found no significant differences between addicts and controls in the volume of that structure.
They found that 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. They also found 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 approximat
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