Binding of what and where during working memory maintenance.

Prefrontal cortex (PFC) supports the maintenance of currently relevant information in working memory (WM). How the PFC is organized for the maintenance of disparate information, how this information is conjoined into a unified whole, and how the representation may change with task demands is still debated. The pattern of neural activity during maintenance of either abstract visual patterns, locations, or their "conjunction" was measured in two experiments using functional magnetic resonance imaging (fMRI). During delays, common regions in PFC were active, but a dorsal-ventral/spatial-nonspatial functional topography distinguished among the three delay types. During conjunction delays, no additional neural architecture was recruited. Instead, conjunction delays were characterized by a significant reduction compared to the response of that cortical region while maintaining its "preferred" information. A model is presented, extending the principles of "biased competition" to the PFC and the dynamic maintenance of information in WM, that accounts for current and seemingly contradictory previous results from both imaging and physiological studies. In this schema, the PFC is not only the source of biasing signals targeting earlier processing regions, but is also the target of these signals. This model stands as an alternative to traditional "domain specific" and "domain general" models of frontal organization of WM, and as an extension of earlier models of PFC mechanisms related to the cognitive control of goal directed behavior.