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The article comments on reports within the issue by researchers M. M. Yartsev and colleagues and J. G. Heys and team on the perception and neural coding of three-dimensional (3D) space in mammal brains, with particular focus on the mapping of place cell neurons in the hippocampus and grid cells in the medial entorhinal cortex. Yartsev and team looked at brain theta wave activity and 3D space encoding of hippocampal neurons of bats in flight. Heys and team compared theta rhythms of medial entorhinal cortex grid cells of bats and rats related to space coding.

A growing body of work is investigating the use of mental maps during decision-making. Here we discuss how decision-making organizes experiences according to an internal model of the current task, thereby structuring memory. Likewise, we consider how the structure of mental maps contributes to decision-making. [ABSTRACT FROM AUTHOR]

Anticipating the future is a key motif of the brain, possibly supported by mental simulation of upcoming events. Rodent single-cell recordings suggest the ability of spatially tuned cells to represent subsequent locations. Grid-like representations have been observed in the human entorhinal cortex during virtual and imagined navigation. However, hitherto it remains unknown if grid-like representations contribute to mental simulation in the absence of imagined movement. Participants imagined directions between building locations in a large-scale virtual-reality city while undergoing fMRI without re-exposure to the environment. Using multi-voxel pattern analysis, we provide evidence for representations of absolute imagined direction at a resolution of 30° in the parahippocampal gyrus, consistent with the head-direction system. Furthermore, we capitalize on the six-fold rotational symmetry of grid-cell firing to demonstrate a 60° periodic pattern-similarity structure in the entorhinal cortex. Our findings imply a role of the entorhinal grid-system in mental simulation and future thinking beyond spatial navigation. [ABSTRACT FROM AUTHOR]