We used fMRI to investigate how the information content of a stimulus influences activity in brain systems that support decision making. Subjects learned decision rules that were based upon the color, shape, or fill pattern of a series of stimuli. Each stimulus was classified by its information content, defined formally by the decision rules it excluded. While activity in dorsolateral prefrontal cortex (dlPFC) increased with increasing stimulus information, activity in the striatum did not. In contrast, within both the striatum and dlPFC, stimuli consistent with the rule evoked greater activity than stimuli inconsistent with the rule. This dissociation indicates that dlPFC supports modification of sets of stimulus-response contingencies while the striatum supports stimulus-specific learning.