Figure 4.

Activity on first two time steps. (A) The array of concentric circles due to summation of synaptic input from all heading angle cells at a 7 by 7 array of heading angle spatial phases. The centers fall at different locations dependent on the different spatial phases of the heading angle cells. (B) Initial random activity in the grid cell population shown for all 30 by 30 spatial phases of grid cells. (C) Feedback from the random grid cell activity in (B) interacts with the corresponding array of heading angle cells at the same spatial phases. Where there is high activity in the grid cell initial random activity, the summation of synaptic input from heading angle planes yields a strong concentric circle input. Where random activity in the grid cells falls below threshold the synaptic input from heading angle cells is absent. (D) The heading angle synaptic input in (C) regulated by random feedback is summed together across the grid cell plane to generate a pattern of activity that already shows peaks of activity falling in a hexagonal pattern due to the overlap of concentric circles.