Hippocampal representations switch from errors to predictions during acquisition of predictive associations

We constantly exploit the statistical regularities in our environment to help guide our perception. The hippocampus has been suggested to play a pivotal role in both learning environmental statistics, as well as exploiting them to generate perceptual predictions. However, it is unclear how the hippocampus balances encoding new predictive associations with the retrieval of existing ones. Here, we present the results of two high resolution human fMRI studies (N=24 for both experiments) directly investigating this. Participants were exposed to auditory cues that predicted the identity of an upcoming visual shape (with 75% validity). Using multivoxel decoding analysis, we found that the hippocampus initially preferentially represented unexpected shapes (i.e., those that violated the cue regularities), but later switched to representing the cue-predicted shape regardless of which was actually presented. These findings demonstrate that the hippocampus in involved both acquiring and exploiting predictive associations, and switches between these modes depending on whether learning is ongoing or complete.