Figure 6: Model of episodic encoding and retrieval of trajectories. Top: Schematic representation of connectivity between grid cells, place cells, and head direction (HD) cells. Bottom: example of trajectory retrieval activity in each region. Trajectory experienced during encoding is shown in gray. (a) The location coded by the oscillation phase of entorhinal grid cell membrane potential is plotted as a dashed line that follows the actual trajectory in gray. Grid cell phase is put through the inverse head direction transformation to obtain coded location. Phase shifts are driven by retrieved head direction until next place cell is activated, then phase moves in new direction dependent on next active head direction cell. (b) Sequentially activated place cell representations are shown as open circles. (c) Each place cell activates a corresponding head direction representation, with direction shown as a short, straight, black line. This drives the next period of update of the grid cell phase.