Predictive grid cells: Future spatial representations in the hippocampal-entorhinal circuit

Place cells in the hippocampus and grid cells in the entorhinal cortex have long been interpreted as neural representations of an animal's current location in space. However, an increasing amount of theoretical and experimental evidence suggests that the hippocampal-entorhinal circuit may also encode predictive information about future spatial states. Temporal coding such as theta phase precession provide one example of how neural activity can represent spatial trajectories extending beyond the animal's present location. Recent studies further suggest that interactions between the medial entorhinal cortex and the hippocampus play a critical role in organizing such predictive sequences. Despite these advances, the neural mechanisms by which future spatial information is generated and transmitted within the hippocampal-entorhinal circuit remain unclear. Here, we highlight the discovery of predictive grid cells: entorhinal neurons whose spatial firing fields shift systematically relative to the animal's direction of travel. This shift in firing fields occurs such that the cells' activity precedes the animal's future location, encoding prospective spatial information. Predictive grid cells are candidate for neurons that convey future spatial information from the entorhinal cortex to the hippocampus and may also contribute to the organization of theta sequences. This review summarizes classical interpretations of spatial representation and discusses recent findings that support predictive coding in the hippocampal-entorhinal system.