When our experience violates our predictions, it is adaptive to upregulate encoding of novel information, while down-weighting retrieval of erroneous memory predictions to promote an updated representation of the world. We asked whether mnemonic prediction errors promote hippocampal encoding versus retrieval states, as marked by distinct network connectivity between hippocampal subfields. During fMRI scanning, participants were cued to internally retrieve well-learned complex room-images and were then presented with either an identical or a modified image (0-4 changes). In the left hemisphere, we find that CA1-entorhinal connectivity increases, and CA1-CA3 connectivity decreases, with the number of changes. Further, in the left CA1, the similarity between activity patterns during cued-retrieval of the learned room and during the image is lower when the image includes changes, consistent with a prediction error signal in CA1. Our findings provide a mechanism by which mnemonic prediction errors may drive memory updating—by biasing hippocampal states.

A fundamental challenge in the study of learning and memory is to understand the role of existing knowledge in the encoding and retrieval of new episodic information. The importance of prior knowledge in memory is demonstrated in the congruency effect—the robust finding wherein participants display better memory for items that are compatible, rather than incompatible, with their pre-existing semantic knowledge. Despite its robustness, the mechanism underlying this effect is not well understood. In four studies, we provide evidence that demonstrates the privileged explanatory power of the elaboration-integration account over alternative hypotheses. Furthermore, we question the implicit assumption that the congruency effect pertains to the truthfulness/sensibility of a subject-predicate proposition, and show that congruency is a function of semantic relatedness between item and context words.

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Like yin and yang, novelty and familiarity are typically described as separate-yet-complementary aspects of an experience, two ends of a single continuum. However, novelty and familiarity are also multifaceted. For instance, novelty can sometimes result in enhanced mnemonic performance, whereas at other times familiarity is better remembered. As previous investigations focused primarily on the experimental aspect of novelty, the mechanisms supporting conceptual novelty (the novel combination of two previously unrelated existing concepts) remain unclear. Importantly, conceptual novelty can be recognized as such only when compared with preexperimental familiar knowledge, regardless of experimental status. Here we applied a combined repetition suppression/subsequent memory fMRI paradigm, focusing on the conceptual aspect of novelty and familiarity as the subject matter. Conceptual novelty was characterized by sustained neural activity; familiarity, on the other hand, exhibited repetition effects in multiple cortical regions, a subset of which was modulated by successful encoding. Subsequent memory of novelty was associated only with activation differences in a distinct set of regions, including the hippocampus and medial cortical regions. These results suggest that conceptual novelty (a) does not (easily) trigger the repetition suppression phenomenon but requires sustained neural recruitment and (b) activates dedicated encoding mechanisms. Conceptual familiarity, in contrast, allows rapid neural processing that depends upon existing neural representations. Overall, these findings challenge the definition of novelty as a unitary concept. Furthermore, they bear important implications for research into the neural bases of knowledge representation and recognition memory.