| The frontal cortex plays an important role in the active maintenance of information in working memory (WM). While the dissociation between certain information types (i.e. verbal and visuo-spatial) is well established, less clear is a distinction between maintenance of spatial and nonspatial visual information. Two models, "domain specific" and "domain general", have been posited to reflect the organization of information for maintenance within the frontal cortex during WM. However, neither model fully accounts for the data concerning the maintenance of spatial, nonspatial, or the combination of this information. The pattern of neural activity during the maintenance of either abstract visual patterns, locations, or the "binding" of this information was measured using fMR1 during delayed-recognition tasks (Experiments 1 and 2). The patterns of delay period activation demonstrate a dorsal-ventral/spatial-nonspatial functional topography. Within this topography, the "binding" of spatial and nonspatial information as a unified representation recruits the same neural mechanisms as that for either information type alone. No additional neural architecture is recruited for this "bind", nor is the associated delay signal the addition of the responses for either information alone. Rather, the "binding" in WM results in significantly less activity within dorsal and ventral areas compared to the response these areas have to their "preferred" information. The representation of information during the delay periods of these tasks was probed in a series of dual-task behavioral Experiments (3a-e). Results indicate that representations in WM lead to attentional biasing of matching, task-relevant information over that of matching, task-irrelevant information. An aspect of the "to-be-remembered" samples is given attentional prioritization only when that aspect (nonspatial, spatial, or the "binding" of this information) is task relevant, suggesting that the representation for maintenance is highly task dependent. A model of WM is presented that integrates both the current results and results from previous imaging and single-cell physiology studies. This model extends the principles of "biased competition", relying on competitive interactions within, and biasing signals between, dorsal and ventral frontal cortex in order to maintain task-relevant information distributed across the frontal cortex. |
