a, 2D projections of neural population responses during the BW12 experiment for trial periods only. Axes correspond to the first two linear discriminants (LD1 and LD2; arbitrary units). Left column shows LEC population responses, middle column shows CA3 population responses, right column shows MEC population responses, each from an example animal. The wall colour of each trial is indicated by a shade of green (black walls) or purple (white walls), with progression of shade from dark to light indicating the progression of trials. b, Fraction of variance explained by the first 20 principal components for each area. Principal components were computed using PCA on raw data. Lines indicate variance explained for individual animals (n = 3, 3 and 2 animals for LEC, CA3 and MEC, respectively). c, Regressing the first two principal components from PCA results for individual animals against time leads to significant fits for all areas, but substantially higher explained variance for LEC. P < 0.001 (LEC versus CA3, t(4) = 9.79), P < 0.01 (LEC versus MEC, t(3) = 6.13), unpaired t-test. Top row, example fits for individual animals are shown with black lines indicating time, coloured lines indicating regression fit and R2 values indicated for the example fit. Bottom two rows, first two principal components for example fits. d, Illustration of cross-validation procedure: fivefold cross-validation is shown for data containing four temporal epochs, with five time bins in each epoch. A different subset of time bins is used as test data for each iteration of the cross-validation procedure. Actual data consisted of 24 epochs (trial and intertrial periods) with 25 or 14 time bins in each epoch, and tenfold cross-validation was used. e, Z-scored decoding accuracy using cells recorded in a single day (left, P = 0.68, one-sided binomial test, n = 46 days), pairs of consecutive days (middle, P = 0.29, one-sided binomial test, n = 72 pairs), pairs of days separated by half the total number of recording days (right, P = 0.37, one-sided binomial test, n = 44 pairs). f, Decoding accuracy for temporal epoch using behaviour tracking data in place of neural activity (n = 3 animals). ‘All’ tracking data consisted of the animal’s position, velocity, acceleration and head direction. g, Left, decoding accuracy for temporal epoch using BW4 data, compared to decoding accuracy using BW12 data. P = 0.32 (t(5) = 1.09), unpaired t-test; matched population size = 47 cells, n = 4 and 3 animals for BW4 and BW12 respectively. Right, decoding accuracy for wall colour from the BW4 experiment, compared to decoding accuracy using matched data from BW12 experiment. P = 0.35 (t(5) = 1.03), unpaired t-test; matched population size = 47 cells, n = 4 and 3 animals for BW4 and BW12 respectively. h, Decoding accuracy for temporal epoch using BW4 data from the LEC, MEC, CA3, CA2 and CA1. One-way ANOVA, F(4) = 20.78, P < 1 × 10−5, post hoc Bonferroni multiple comparisons test, P < 0.005 (for each comparison against LEC); matched population size = 24 cells, n = 7, 2, 7, 3 and 3 animals for LEC, MEC, CA3, CA2 and CA1 respectively. i, Relation between population size and decoding accuracy for the LEC, CA3 and MEC. Left, decoding accuracy for varying population sizes; each line indicates the curve fit to data (shown as points) from one animal, with colours indicating recording area (n = 3, 3 and 2 animals for LEC, CA3 and MEC, respectively). Right, relation between population size and decoding accuracy for the LEC and CA3, pooled across animals from BW12 and BW4 experiments (data pooled from n = 7 animals for both LEC and CA3). j, Decoding accuracy for wall colour from trial period activity alone for the LEC, CA3 and MEC. P = 0.47 (LEC versus CA3, t(4) = 0.81) unpaired t-test; matched population size = 28 cells, n = 3, 3 and 2 animals for LEC, CA3 and MEC, respectively. k, Decoding accuracy for wall colour using data that was shuffled in time. P = 0.74 (t(2) = 0.38), two-tailed paired t-test; n = 3 animals. l, Decoding accuracy for wall colour using a subpopulation with all wall-colour-selective cells removed, compared to size-matched populations that were randomly drawn from full population. P = 0.12 (t(2) = 2.66), paired t-test; n = 3 animals with 77, 126 and 195 cells not selective for wall colour. For f, g, j–l, circles indicate individual animals, solid lines indicate mean decoding accuracy ± s.e.m., dashed lines indicate chance levels.