For two-room “remapping” experiments, rats would next run a single 20 min session in a hairpin maze in a different room, and later complete a third 20 min run in the maze in the original room,

followed by two 10 min sessions in open field. Rats rested a minimum of 1 hr in their home cage between runs. In the “virtual hairpin” task, each rat was tested in the same arena as the open field task, with two experimenters on either side of the maze delivering vanilla crumbs at the north and south walls in an alternating manner. Baiting positions were moved successively from west to east or vice versa to mimic the running pattern and spacing in the hairpin maze. The training regime resulted in ten north-south laps similar to the hairpin maze (see Movie S1). Spike Selleck Onalespib sorting was performed offline using graphical cluster-cutting Screening Library software (Fyhn et al., 2004). Position estimates were based on tracking of one of the LEDs. The path was smoothed using a 400 ms, 21-sample boxcar smoothing window, position data

were sorted into 3 × 3 cm2 bins, and number of spikes and occupancy time were determined for each bin for all cells with more than 100 spikes. Maps for number of spikes and time were smoothed individually using a quasi-Gaussian kernel over the surrounding 2 × 2 bins (Langston et al., 2010) and firing rates were then determined by dividing spike number and time for each bin. Peak rate was defined as the rate in the bin with the highest rate. Pixels with <20 ms occupancy were omitted. A spatial autocorrelogram based on Pearson's product moment correlation coefficient was calculated for the smoothed rate map of each cell in the open field (Sargolini et al., 2006). In each autocorrelogram, gridness was calculated for multiple circular samples surrounding the center of the autocorrelogram with radii increasing in 3 cm (1 bin) steps from a minimum of 10 cm more than the radius of the central peak to a maximum of 10 cm less than the width of the box. For each circular sample, the grid score was calculated by taking the minimum correlation at rotations Thymidine kinase of 60° and 120° and subtracting the maximum

correlation at 30°, 90°, and 150° (Langston et al., 2010). Grid cells were defined as cells with rotational symmetry-based grid scores that exceeded the 99th percentile of the distribution of grid scores obtained from shuffled data (Figure S2). Spatial coherence was estimated as the mean correlation between the firing rate in each bin and the average firing rate of the eight adjacent bins (Muller and Kubie, 1989). Correlations were calculated from nonsmoothed fields and Fisher z-transformed. Within-trial stability of firing fields was estimated by correlating rate distributions on even and odd minutes (i.e., minutes 0–1, 2–3, etc. against minutes 1–2, 3–4, etc.). Bins visited <150 ms were excluded. Position samples were smoothed using a 15-sample moving mean filter.