Decision making by methamphetamine-dependent subjects is associated with error-rate-independent decrease in prefrontal and parietal activation.

BACKGROUND One important aspect in decision making is how success or failure influences the selection of a response. In a previous investigation, methamphetamine-dependent subjects (MD) selected win-stay/lose-shift consistent responses than normal comparison subjects (NC), which may imply that MD are more influenced by success. This study examined whether the degree of success and the degree of predictability differentially affected MD's decision making. METHODS Using functional magnetic resonance imaging, 14 MD were compared with 14 NC while performing the two-choice prediction task at three success rates and the two-choice response task. RESULTS The increase in win-stay/lose-shift consistent responses by MD relative to NC was independent of success rate. Irrespective of success, MD showed less task-related activation in orbitofrontal cortex (Brodmann's area [BA] 10), dorsolateral prefrontal cortex (BA 9), anterior cingulate (BA 32), and parietal cortex (BA 7). Whereas NC showed success-related patterns of neural activation in the orbitofrontal, dorsolateral prefrontal, and parietal cortex, MD showed activation that was highest when the outcome was most unpredictable. CONCLUSIONS Our results are consistent with the hypothesis of a more rigid stimulus-response relationship during MD's decision making, which may be due to a shift from processing "success" toward processing the degree of stimulus "predictability."