Hippocampal replay anticipates the hexagonal axes that structure human navigation behaviour

Entorhinal grid cells provide a spatial metric through hexagonally periodic firing, whereas hippocampal replay reactivates experience in compressed sequences; whether the two share a directional geometry is unknown. We recorded magnetoencephalography during a direction-resolved navigation task that yielded 1,800 navigation events per participant, allowing both to be estimated event-wise across the full 360{degrees}. Reverse and forward replay emerged early in each event, followed by a six-fold entorhinal code. Replay was anchored to the grid axes, with forward and reverse replay encoding opposite directions of each axis and together spanning the six-fold structure. In a continuous-attractor network, replay along the hexagonal axes produced higher gridness than movement-axis or no replay. Behaviourally, an early modulation of movement speed was followed by a two-fold modulation of trajectory deviation whose phase aligned to the hexagonal axes. These results link a single hexagonal geometry across replay, entorhinal coding, and behaviour.