Recording setup and CA1 place cell firing fields. (A) Place cells were recorded in a white round-cornered square box (40 × 40 cm, 30 cm high). The box was housed in a 180 × 120 cm soundproof room. A brown paper towel was hung on the wall of the box as a local cue. (B) The animal’s position was tracked using a video camera (upper). Color-coded firing rate maps for CA1 cells in the recording box (lower). Red indicates maximum rate, blue indicates silent. Regions not visited by the mouse are shown in gray. Spike waveforms recorded by each electrode are shown in the right side. (C) Representative place fields of CA1 place cells in control (upper) and mutant mice (lower). Each recording time was 15 min. (D) The correlation coefficient (left) and the value of place field shift (right) between the two place fields is shown at the side of the maps. Brown areas in the right panels indicate place fields (pixels whose firing rates exceed the overall mean firing rate + SD). White dots indicate the center of mass of the place fields. Place field shift was defined by the displacement of the center of mass of the place field. (E) Histograms of total place field size of CA1 cells in control (upper) and mutant mice (lower). (F) Histograms of largest place field size in control (upper) and mutant mice (lower). (G) Correlation coefficients of two place fields recorded successively in the same environment are displayed. Each recording time was 7.5 min. (H) The shift of place fields recorded successively in the same environment is displayed. Values in panel (E, F, G, H) indicate mean ± S.E.M. Significance was evaluated using the Wilcoxon rank sum test.