Figure 7. A large-scale 3–5 Hz network originating from both hippocampi. A, Ratio of concentration parameters during the period of interest divided by baseline, along the LFP range. The 1 lines indicate no difference between frontal cortex FRs and baseline. In all three regions, but mainly for the couples LH-FC and RH-FC, the peak of synchrony is at 4–5 Hz. B, Distribution of phase differences at each respective peak of synchrony (LH-FC, 5 Hz; LH-RH, 5 Hz; RH-FC, 4 Hz). For all three regions, phase differences are significantly more concentrated, indicating a synchronization across regions during the period of interest (test for equal concentration parameter κ, **p < 0.01, ****p < 0.0001). Y-scale, number of tested time frames per phase bin (for each subplot of B, the vertical y-scale indicates 203 tested time frames). C, Cross-correlation at 3–5 Hz. The best correlation between activities in LH, FC, and RH is when the activity in the LH and RH is shifted backward by 64 and 52 ms, respectively, indicating that the LH and RH activity precedes the FC activity. When using the cross-correlation matrix between the LH and RH as a control (their delay being close to zero), we obtained a significantly different delay for the couples LH-FC and RH-FC (Kruskal–Wallis test, both at p < 0.0001). The y-axis indicates how many events (i.e., FC-FRs) present a maximal correlation at 3–5 Hz for each time-bin (x-axis). D, Partial directed coherence (PDC) at 3–5 Hz (top). As shown, the driving from the LH and RH toward the FC increases significantly during the period of interest (Kruskal–Wallis test + Dunn’s post hoc test: *p < 0.05, **p < 0.01, ****p < 0.0001), supporting a causative role of both hippocampi in the 3–5 Hz frontal activity. Along the LFP range (below), the increased PDC is specific for low frequencies (LH toward FC, 2–14 Hz; RH toward FC, 0–29 Hz; Kruskal–Wallis test + Dunn’s post hoc, p < 0.0001, significant values in yellow). The table on the right compares the median iAPDC value for each connectivity measured during baseline and during FC-FR. The fourth column (diff) indicates the increase or the decrease in the iAPDC between baseline and FC-FR in percentages.