Figure 5.

Movement of the grid cell activity induced by speed modulation of head direction input. (A) With constant speed and with head direction facing West, the network receives greater input from the heading angle line coding West. This causes a progressive shift in the population activity of the grid cell plane, resulting in the hexagonal pattern shifting to the West. (B) This shift occurs because of the distortion in the circular pattern of synaptic input. The synaptic weights do not change, but the greater amplitude of oscillations in heading angle cells coding angles closer to West distorts the magnitude of synaptic input from each array of heading angle cells, resulting in a progressive shift of grid cell activity to the West. Feedback from the grid cell plane to the heading angle plane causes a progressive shift in the synaptic input. (C) Expansion of the synaptic input from the heading angle neurons coding a single spatial phase shows that on successive time steps 11–13 the circles show a distortion toward the West. Rhythmic regulation of the network prevents activity during the period when the same heading angle input would distort the pattern toward the East. (D1) A polar plot shows the amplitude of response of a heading angle cell with an angle of 180° (West). The arrow shows how the input velocity causes a maximum change in amplitude (3.0) for this heading angle cell. (D2) A heading angle cell with angle of 135° (Northwest) has a smaller change in amplitude (2.4). (D3) A heading angle cell with angle of 90° (North) shows no change in response for this velocity, but maintains the background amplitude (1.0).