How autobiographical memories are represented in the human brain and whether this changes with time are questions central to memory neuroscience. Two regions in particular have been consistently implicated, the ventromedial prefrontal cortex (vmPFC) and the hippocampus, although their precise contributions are still contested. The key question in this debate, when reduced to its simplest form, concerns where information about specific autobiographical memories is located. Here, we availed ourselves of the opportunity afforded by multivoxel pattern analysis to provide an alternative to conventional neuropsychological and fMRI approaches, by detecting representations of individual autobiographical memories in patterns of fMRI activity. We examined whether information about specific recent (two weeks old) and remote (10 years old) autobiographical memories was represented in vmPFC and hippocampus, and other medial temporal and neocortical regions. vmPFC contained information about recent and remote autobiographical memories, although remote memories were more readily detected there, indicating that consolidation or a change of some kind had occurred. Information about both types of memory was also present in the hippocampus, suggesting it plays a role in the retrieval of vivid autobiographical memories regardless of remoteness. Interestingly, we also found that while recent and remote memories were both represented within anterior and posterior hippocampus, the latter nevertheless contained more information about remote memories. Thus, like vmPFC, the hippocampus too respected the distinction between recent and remote memories. Overall, these findings clarify and extend our view of vmPFC and hippocampus while also informing systems-level consolidation and providing clear targets for future studies.

Much evidence from distinct lines of investigation indicates the involvement of angular gyrus (AnG) in the retrieval of both episodic and semantic information, but the region's precise function and whether that function differs across episodic and semantic retrieval have yet to be determined. We used univariate and multivariate fMRI analysis methods to examine the role of AnG in multimodal feature integration during episodic and semantic retrieval. Human participants completed episodic and semantic memory tasks involving unimodal (auditory or visual) and multimodal (audio-visual) stimuli. Univariate analyses revealed the recruitment of functionally distinct AnG subregions during the retrieval of episodic and semantic information. Consistent with a role in multimodal feature integration during episodic retrieval, significantly greater AnG activity was observed during retrieval of integrated multimodal episodic memories compared with unimodal episodic memories. Multivariate classification analyses revealed that individual multimodal episodic memories could be differentiated in AnG, with classification accuracy tracking the vividness of participants' reported recollections, whereas distinct unimodal memories were represented in sensory association areas only. In contrast to episodic retrieval, AnG was engaged to a statistically equivalent degree during retrieval of unimodal and multimodal semantic memories, suggesting a distinct role for AnG during semantic retrieval. Modality-specific sensory association areas exhibited corresponding activity during both episodic and semantic retrieval, which mirrored the functional specialization of these regions during perception. The results offer new insights into the integrative processes subserved by AnG and its contribution to our subjective experience of remembering.

Recent theoretical perspectives have suggested that the function of the human hippocampus, like its rodent counterpart, may be best characterized in terms of its information processing capacities. In this study, we use a combination of high-resolution functional magnetic resonance imaging, multivariate pattern analysis, and a simple decision making task, to test specific hypotheses concerning the role of the medial temporal lobe (MTL) in scene processing. We observed that while information that enabled two highly similar scenes to be distinguished was widely distributed throughout the MTL, more distinct scene representations were present in the hippocampus, consistent with its role in performing pattern separation. As well as viewing the two similar scenes, during scanning participants also viewed morphed scenes that spanned a continuum between the original two scenes. We found that patterns of hippocampal activity during morph trials, even when perceptual inputs were held entirely constant (i.e., in 50% morph trials), showed a robust relationship with participants' choices in the decision task. Our findings provide evidence for a specific computational role for the hippocampus in sustaining detailed representations of complex scenes, and shed new light on how the information processing capacities of the hippocampus may influence the decision making process. © 2011 Wiley Periodicals, Inc.