Supplementary Figure 11: Preserved temporal coding in iCre-KO mice.

(a) Field size on the linear track was larger in iCre-KO mice (mean ± SD; iWT = 22.98 ± 11.56, iCre-KO = 30.39 ± 14.92, two-tailed WRS Z = −2.26, p = 0.023; n = 42 fields from 30 cells from 3 iWT mice, 38 fields from 28 cells from 4 iCre-KO mice). *p<0.05. (b) As an alternative approach, we also estimated field width from the population vector cross-correlation matrices for iWT and iCre-KO place cells (n = 30 iWT, 28 iCre-KO place cells)^{8, 9}. Decorrelation curves, at right, show the mean correlation ± SEM for all possible population vector pair distances between 0 and 15 bins (2.5 cm each). Field width was estimated as the mean distance from the diagonal matrix to the population vectors with a mean correlation of 0.2 (iWT = 28.8 ± 8.1 cm, iCre-KO = 34.2 ± 8.5 cm, two-tailed WRS Z = −2.12, p = 0.034) (c) Histograms of the slopes of regression lines fit between normalized field position and spike phase in iWT (left, n = 26) and iCre-KO (right, n = 23) fields. Filled bars represent significant slopes (p < 0.05). The gray region delimits negative slopes. There was no difference in the proportion of fields with negative slopes (iWT = 17/26, 0.65, iCre-KO = 18/23, 0.78, two-tailed binomial test, Z = −1.00, p = 0.32) or with significant slopes (iWT = 6/26, 0.23, iCre-KO = 6/23, 0.26, two tailed binomial test, Z = −0.24, p = 0.81). Insets: mean place-phase firing maps for all fields with negative slopes. Warm colors indicate the position-phase bins with the highest instantaneous firing rates, cool colors indicate those with lowest instantaneous firing rates. In no bin did the difference between the two group- averaged maps exceed the 95% confidence interval (see Methods). (d) Boxplot for position-phase slopes for all iWT and iCre-KO fields (open boxes; n = 26 iWT fields, 23 iCre-KO fields), and significant slopes (filled boxes; n = 6 iWT fields, 6 iCre-KO fields). Individual data points for significant slopes are overlaid (black circles). The slopes did not differ between iWT and iCre-KO mice (mean ± SD; significant slopes: iWT = −270.61 ± 298.48°/field, iCre-KO = −321.56 ± 236.45°/field, two-tailed WRS p = 0.82; all slopes: iWT = −116.86 ± 345.60°/field, iCre-KO = −190.19 ± 254.16°/field, two-tailed WRS Z = 0.51, p = 0.61). (e) Individual examples of iWT (left) and iCre-KO (right) fields displaying significant phase precession. Left: Theta phase and location of spikes emitted while the mouse was running through the place field indicated at right. The peak of the theta oscillation is set to 360 degrees, and corresponds to the most positive portion of the cycle recorded in the EEG of the CA1 pyramidal layer. The phase of each spike is plotted in a second cycle to aid visualization. Right: the place field recorded on the linear track. Histogram of firing rates across the track, with green lines indicating the boundaries of the place field. The direction of travel for the field is indicated by the arrow. A 2D heat map is shown below, with unexplored bins depicted in black. The corresponding place field recorded in the open field arena is shown at top, with black dots indicating the center of mass of each field detected. For all heat maps, warm colors denote higher firing rates, cool colors denote lower firing rates. (f) Left: Boxplot showing running speed along the analyzed portion of the linear track (central 70 cm). There was no difference in running speed between groups (mean ± SD; iWT = 9.03 ± 4.55 cm/s, iCre-KO = 7.20 ± 2.74 cm/s, two-tailed WRS Z = 1.32, p = 0.19, n = 22 sessions from 3 iWT mice, 20 sessions from 4 iCre-KO mice). Right: Running speed versus track position for iWT (top) and iCre-KO (bottom) mice. Solid line depicts the mean across sessions (n = 22 sessions from 3 iWT mice, 20 sessions from 4 iCre-KO mice), gray region denotes the standard deviation of the mean. (g-i) Analysis of sharp wave ripples (SWRs) during linear track sessions when place cells were recorded (n = 16 sessions from 3 iWT mice, 13 sessions from 4 iCre-KO mice). (g) The frequency of SWRs during periods of awake rest did not differ significantly between iWT and iCre-KO mice (mean ± SD; iWT = 0.11 ± 0.12 SWRs/s, iCre-KO = 0.16 ± 0.16 SWRs/s, two-tailed WRS Z = −1.25, p = 0.21). (h) The number of spikes per cell per SWR event did not differ significantly between iWT and iCre-KO place cells (mean ± SD; iWT = 0.61 ± 0.44 spikes/SWR, iCre-KO = 0.51 ± 0.39 spikes/SWR, WRS Z = 0.94, p = 0.35). The number of spikes per cell per second of awake rest also did not differ between groups (mean ± SD; iWT = 0.073 spikes/s, iCre-KO = 0.089 spikes/s, two-tailed WRS Z = −0.22, p = 0.83). These analyses include all place cells that fired at least one spike during at least one SWR event (n = 21 iWT cells, 24 iCre-KO cells). (i) The percentage of SWR events for which a cell fired at least one spike was not significantly different between iWT and iCre-KO place cells (mean ± SD; iWT = 27.0 ± 30.0%, iCre-KO = 26.0 ± 19.0%, two-tailed WRS Z = −0.47, p = 0.64; n = 30 iWT place cells, 28 iCre-KO place cells). Data in panels (a, d, f, g-i) are represented as boxplots: the first and third quartiles are depicted by a box, and the median by a solid line. Whiskers indicate the range, except for data falling above the third quartile or below the first quartile by at least 1.5 times the interquartile range. Outliers are denoted by plus symbols.

8. Maurer, A.P., Vanrhoads, S.R., Sutherland, G.R., Lipa, P. & McNaughton, B.L. Self-motion and the origin of differential spatial scaling along the septo-temporal axis of the hippocampus. Hippocampus 15, 841–852 (2005).

9. Ormond, J. & McNaughton, B.L. Place field expansion after focal MEC inactivations is consistent with loss of Fourier components and path integrator gain reduction. Proc Natl Acad Sci U S A 112, 4116–4121 (2015).