Hexadirectional modulation of high-frequency electrophysiological activity in the human anterior medial temporal lobe maps visual space

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 data sets: non-invasive magnetoencephalography (MEG) in healthy subjects and entorhinal intracranial EEG recordings in an epileptic patient. Both data sets 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 its millisecond accuracy, MEG recordings allow to link 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.