Criterion-setting in the left prefrontal cortex: the roles of process and domain

A large amount of previous evidence suggests that criterion-setting processes can be localized to the left prefrontal cortex (PFC). However, others point out that these results may be confounded by the task domain, namely verbal. Indeed, some studies show that right PFC activation is seen with spatial tasks. This study used fMRI to test the domain generality of the left PFC in a novel rule discovery task in both the verbal and spatial domains. Twenty healthy young adult participants were asked to discover the rule underlying the presentation of a series of letters in varied spatial locations. Twenty rules were presented in separate blocks: ten verbal rules, in which the letters formed words pertaining to a single semantic category, and ten spatial rules, in which the letters formed geometric figures. Additionally, in half of the blocks the domain to which the rule belonged was indicated, while in the other half the domain was not indicated and the participant needed to search both domains (parallel search). A conjunction analysis of the three search types (verbal, spatial, parallel) revealed that the left ventrolateral PFC is involved in all three search types. These data support a domain general role of the left PFC.