John Lisman : The neural systems for spatial localization and exploration: role of 10 identified cell types

The hippocampal/entorhinal place system has many cell types, but how they function together remains unclear. Here we propose that the fundamental function of grid cells is to produce mind-travel, a process that allows access to associations with potential upcoming positions. To account for properties of phase precession, we propose that mind travel occurs selectively during the second half of each theta cycle (driven by head-direction cells); in the first half, current place is computed by combining sensory information from the lateral entorhinal cortex with path integration information from the medial entorhinal cortex. Because the computations that produce mind-travel and path integration are difficult to combine, we suggest that path integration is computed in a separate network.