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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., Competing Interests: The authors declare that no competing interests exist.

Summary Grid cells are one of the core building blocks of spatial navigation [ 1 ]. Single-cell recordings of grid cells in the rodent entorhinal cortex revealed hexagonal coding of the local environment during spatial navigation [ 1 ]. Grid-like activity has also been identified in human single-cell recordings during virtual navigation [ 2 ]. Human fMRI studies further provide evidence that grid-like signals are also accessible on a macroscopic level [ 3–7 ]. Studies in both non-human primates [ 8 ] and humans [ 9, 10 ] suggest that grid-like coding in the entorhinal cortex generalizes beyond spatial navigation during locomotion, providing evidence for grid-like mapping of visual space during visual exploration—akin to the grid cell positional code in rodents during spatial navigation. However, electrophysiological correlates of the grid code in humans remain unknown. Here, we provide evidence for grid-like, hexadirectional coding of visual space by human high-frequency activity, based on two independent datasets: non-invasive magnetoencephalography (MEG) in healthy subjects and entorhinal intracranial electroencephalography (EEG) recordings in an epileptic patient. Both datasets consistently show a hexadirectional modulation of broadband high-frequency activity (60–120 Hz). Our findings provide first evidence for a grid-like MEG signal, indicating that the human entorhinal cortex codes visual space in a grid-like manner [ 8–10 ], and support the view that grid coding generalizes beyond environmental mapping during locomotion [ 4–6, 11 ]. Due to their millisecond accuracy, MEG recordings allow linking of grid-like activity to epochs during relevant behavior, thereby opening up the possibility for new MEG-based investigations of grid coding at high temporal resolution. Highlights • Hexadirectional modulation of human high-frequency electrophysiological activity • Grid-like mapping of visual space in the human entorhinal cortex • Grid-coding beyond environmental mapping during locomotion Staudigl et al. show grid-like modulation of human high-frequency activity in non-invasive magnetoencephalographic and intracranial EEG recordings. The results indicate that the human entorhinal cortex codes visual space in a grid-like manner, supporting the view that grid coding generalizes beyond environmental mapping during locomotion. [ABSTRACT FROM AUTHOR]