Rule-dependent prefrontal cortex activity across episodic and perceptual decisions: an fMRI investigation of the criterial classification account.

Although lateral prefrontal cortex (LPFC) is clearly involved in decision-making, competing functional characterizations exist. One characterization posits that activation reflects the need to select among competing representations. In contrast, recent fMRI research suggests that activation is driven by the criterial classification of representations, even with minimal competition. To adjudicate between these hypotheses, we used event-related fMRI and contrasted tasks that required different numbers of criterial classifications prior to response in both perceptual and memory domains. Additionally, we manipulated the level of interstimulus competition by increasing the number of probes. Experiment 1 demonstrated that LPFC activation tracked the number of intermediate classifications during trials yet was insensitive to the number of competing probes and the behavioral decline accompanying competition. Furthermore, Experiment 2 demonstrated equivalent increases in LPFC activation for a task requiring two overt criterial classifications (independent classification) and one requiring two covert criterial classifications prior to the single overt response (same-different judgment). As found in Experiment 1, both tasks showed greater activation than a judgment requiring only one classification act (forced choice). These data indicate that LPFC responses reflect the number of executed criterial classifications or judgments, independent of the number of competing stimuli and the overt response demands of the decision task.