Extended Data Figure 7: Cross-frequency coupling of 20–40-Hz oscillations to local theta oscillations in LEC and pCA1.

a–d, Relationship of 20–40-Hz oscillations in LEC to phase of local theta oscillations, plotted as in Fig. 2d–g (n = 10 tetrodes from 5 rats). a, Theta phase distribution of 20–40-Hz oscillation maxima at T1, T3, T5 and on error trials at T5 (T5e). 0° was defined as the trough of the theta cycle. Note that theta oscillations exist in LEC and that 20–40-Hz oscillations are moderately phase-coupled with theta oscillations already at T1. b, Mean vector length calculated from theta phase distribution of 20–40-Hz oscillation maxima at T1–T5. The degree of cross-frequency coupling did not change significantly across the learning period (T1–T5, repeated measures ANOVA: F(4, 36) = 1.7, P = 0.17). No difference was observed on error trials (T5e, compared with T5d using a two-tailed paired t-test, t(9) = 0.78, P = 0.45). c, Representative cross-frequency coherence plot showing for LEC that power of 20–40 Hz oscillations (y-axis) is modulated by theta phase (x-axis) during cue sampling at T5. Coupling strength is colour-coded (dark blue, no coupling; red, maximal coupling). d, Top, time-resolved power spectrum averaged across all theta cycles with 20–40-Hz oscillations at T5 in LFP from 10 tetrodes in all 5 rats. t = 0 corresponds to the theta trough. Bottom, averaged unfiltered theta cycle. 20–40-Hz oscillations occurred at the falling phase of the theta wave. e–h, Similar plots for pCA1 (n = 14 tetrodes from 5 rats; e, theta phase distribution; f, mean vector length; g, cross-frequency coherence plot; h, time-resolved power spectrum). Animals with implants in pCA1 were recorded only after the completion of learning, that is, only at T5. In pCA1, oscillations at ∼30–50-Hz were phase-coupled with theta oscillations. The degree of coupling did not change on error trials (two-tailed paired t-test, t(13) = 1.29, P = 0.22). i, Same plots as in Fig. 2f, but with wider 60° bins. The diagram shows the relationship of 20–40-Hz oscillations in dCA1 to the phase of local theta oscillations (n = 10 tetrodes from 5 rats). The use of wider bins did not change the results. Significant cross-correlations between cell pairs in LEC and CA1 were not found, as expected due to the sparse connectivity between cell pairs in these areas¹³. j, Theta phase distribution of 20–40-Hz oscillation maxima for LFP from dCA1 as in Fig. 2f, but during the pre-cue period, at time points T1, T3, T5 (n = 10 tetrodes from 5 rats, means ± s.e.m.). k, Mean vector length calculated from theta phase distributions of 20–40-Hz oscillation maxima during the pre-cue period did not change during the course of training (repeated measures ANOVA: F(4, 36) = 0.26, P = 0.90; n = 10 tetrodes from 5 rats). Vector lengths during cue sampling was increased compared to the pre-cue period at T5 (paired t-test, P < 0.05; t(9) = 2.5) but not at T1–T4 (P > 0.05; t(9) < 1.9).