Figure 2.

Illustration of the methods used to test HD cells' responses to landmark shifts, removal of visual cues, and path integration (spatial updating) between a familiar and novel environment. A, Progression of recording sessions for a HD cell within the standard recording environment. After an initial standard recording session, the single salient landmark, a white cue card attached to the inside cylinder wall, is rotated 90° from its original position for Session 2 and then shifted back for Session 3. Each cue rotation occurred with the rat outside the cylinder. After this rotation test, the cue is removed and the lights are extinguished for Session 4, then the cue is returned and lights reilluminated for Session 5. The animal is disoriented outside of the recording environment before each session. B, Diagram of the dual-chamber apparatus used to test path integration. After recording the HD cell in the familiar, cylindrical environment, the animal must locomote to a completely novel rectangular environment. The cell is recorded continuously as the animal moves between the two chambers.