FIGURE 7-8 Classes of Spatially Related Cells in the Hippocampal Formation (A and B) Place cells discharge when a rat is at a spatial location, irrespective of its orientation. (C) Head-direction cells discharge to indicate where the rat’s head points, irrespective of its location. (D) Grid cells discharge at many locations, forming a virtual grid that is invariant in the face of changes in the rat’s direction, movement, or speed. At right in each part, xy coordinates indicate the directional selectivity of the cell recorded at left.

Courtesy of John O’Keefe.