Abstract
Most working memory research focuses on our representations of the past. However, the utility of working memory lies in how it helps us prepare for the future. Despite this, little research examines representations that guide future cognition. Here, we examined neural representations of the past versus future in working memory. Participants followed a five-location sequence on the left and right side of the screen while being scanned with fMRI. On each trial, a cue pointed to the side that would be tested by an upcoming memory probe. After a delay, the probe tested for the identity of the stimulus that followed the previously presented item in the cued side’s sequence. We submitted the average activations for each time point to a multiple regression analysis to investigate the role of visual and parietal areas in memory for the past versus the future. Activation in visual cortex and intraparietal sulcus transitioned away from representing the presented probe (the past) by the onset of the cue, demonstrating a period of “activity-silence.” Following cue onset, we found ramping evidence for representation of the next item in the sequence (the future). Follow-up analyses indicated this future representation was part of a more general representation reflecting the probability of future stimuli. Hence, working memory appears to encode our expectations for the future. We argue that the retrospective codes commonly observed in working memory paradigms may be a reflection of the expectation of a test stimulus that matches the past. These findings begin to make clear that working memory is indeed “working” prospectively to guide thoughts and actions.