Are Representations in Working Memory Distinct From Representations in Long-Term Memory?

Neural activation in a 12-item probe-recognition task was examined to investigate the contribution of the hippocampus to long-term memory (LTM) retrieval and working memory (WM) retrieval. Results indicated a dissociation between the last item that participants studied and other items of the study list: Compared with all other serial positions, activation was reduced for the item in the most recent position (for which no items intervened between study and test). This finding suggests that this last item was in focal attention at test time, and, therefore, no retrieval operation was required to access it. However, contra the assertion that the hippocampus should selectively support LTM, activation of the medial temporal lobe was observed for all serial positions other than the last position, and activation level could be predicted from the underlying memory strength. Collectively, these findings support single-store accounts that assume there are similar operating principles across WM and LTM representations, and the focus of attention is limited.