Active Neural Representation of Stimulus Categories Outside of the Focus of Attention

Previous research on the brain correlates of working memory using functional magnetic resonance imaging (fMRI) and multivariate pattern analysis (MVPA) have shown that neural activity related to information currently needed to respond on a test is considered to be in the focus of attention (FoA). An ongoing controversy pertains to the neural representation of information in working memory that is not needed for the upcoming test but possibly for a subsequent one, which is considered to reside in an activated portion of long-term memory (aLTM). The key theoretical issue regarding aLTM is whether it corresponds solely to an activity-silent neural state. Here, by using a retrospective cuing task in which two arrays of stimuli from different categories were presented in succession on the same trial, and a pattern classifier trained on the first-presented category during the presentation of the second, we provide evidence that aLTM is associated with an active neural state. Specifically, the aLTM effect was demonstrated to be dissociable in direction from that related to the FoA, there was considerable overlap between brain regions representing information in a stronger form in the FoA and a weaker form in aLTM, and the two states appeared to be differentially subject to flexible cognitive control versus natural decay.