Fig. 7.

Average cross-frequency coherence for theta (7–10 Hz) and the 2nd harmonic (14–20 Hz) phase. When the coherence is averaged for these specific phases, there is a considerable change in cross-frequency coherence with velocity. Each panel shows the individual layers of the hippocampus, with yellow as the high-velocity (>35 cm/s) bin and blue as the 5–15 cm/s bin. The lines and shading depict the mean ± SE (n = 5). Note that in the gamma range, greater than ~50 Hz, there is an increase in coherence that is associated with a shift of the maximum value to higher frequencies (see Fig. 3). The changes in the low-value frequencies, <40 Hz, are attributed to the higher order harmonics of theta (e.g., 24 and 32 Hz; see bicoherence analysis in Figs. 8 and 9).