During working memory retrieval, proactive interference (PI) can be induced by semantic similarity and episodic familiarity. Here, we used fMRI to test hypotheses about the role of the left inferior frontal gyrus (LIFG) and the medial temporal lobe (MTL) regions in successful resolution of PI. Participants studied six-word lists and responded to a recognition probe after a short distracter period. We induced semantic PI by using study lists containing words within the same semantic category (e.g., animals). We also measured PI induced by recent study, which should increase episodic familiarity, by comparing recent negative probes (lures studied in previous trial) to distant negative probes (lures that had not been presented within a block). Resolving both types of PI resulted in enhanced activation in LIFG and MTL regions. We propose that the LIFG and the MTL support successful resolution of interference via controlled retrieval processes that serve to recover detailed episodic (e.g., list-specific or source) information: Specifically, the data suggest that BOLD activation in the LIFG reflects the deployment of controlled retrieval operations, regardless of whether the retrieval attempt succeeds in recovering the target information, whereas MTL activation specifically reflects access to relevant episodic information that serves to successfully resolve PI.

Functional magnetic resonance imaging was used to identify regions involved in working memory (WM) retrieval. Neural activation was examined in two WM tasks: an item recognition task, which can be mediated by a direct-access retrieval process, and a judgment of recency task that requires a serial search. Dissociations were found in the activation patterns in the hippocampus and in the left inferior frontal gyrus (LIFG) when the probe contained the most recently studied serial position (where a test probe can be matched to the contents of focal attention) compared to when it contained all other positions (where retrieval is required). The data implicate the hippocampus and the LIFG in retrieval from WM, complementing their established role in long-term memory. Results further suggest that the left posterior parietal cortex (LPPC) supports serial retrieval processes that are often required to recover temporal order information. Together, these data suggest that the LPPC, the LIFG, and the hippocampus collectively support WM retrieval. Critically, the reported findings support accounts that posit a distinction between representations maintained in and outside of focal attention, but are at odds with traditional dual-store models that assume distinct mechanisms for short- and long-term memory representations.

Although research on the neural bases of language has made significant progress on how the brain accesses the meanings of words, our understanding of sentence-level semantic composition remains limited. We studied the magnetoencephalography (MEG) responses elicited by expressions whose meanings involved an element not expressed in the syntax, which enabled us to investigate the brain correlates of semantic composition without confounds from syntactic composition. Sentences such as the author began the book , which asserts that an activity was begun although no activity is mentioned in the syntax, were contrasted with control sentences such as the author wrote the book , which involved no implicit meaning. These conditions were further compared with a semantically anomalous condition ( the author disgusted the book ). MEG responses to the object noun showed that silent meaning and anomaly are associated with distinct effects, silent meaning, but not anomaly, eliciting increased amplitudes in the anterior midline field (AMF) at 350–450 msec. The AMF was generated in ventromedial prefrontal areas, usually implicated for social cognition and theory of mind. Our results raise the possibility that silent meaning interpretation may share mechanisms with these neighboring domains of cognition.