Fig. 2
During freezing, the neural activity in the OB and plPFC is dominated by highly correlated ~4-Hz oscillations. a Example OB and plPFC LFPs during a freezing epoch. Filtered signals (2–6 Hz) are overlaid on raw traces (gray). Nissl-stained coronal brain sections show electrode sites. Scale bars, 0.5 mm top and 1.0 mm bottom. b Time-frequency cohereogram of OB and plPFC LFPs during a portion of a retrieval session in which freezing was observed (marked in blue). High phase coherence emerges during periods of freezing. c Spectral coherence between simultaneously recorded OB and plPFC LFPs during non-freezing (from pre-tone baseline, black) and freezing (blue) periods (mean ± SEM, n = 8 mice). Inset, averaged peak coherence for non-freezing and freezing periods (0.69 ± 0.06 to 0.88 ± 0.03, n = 8, Wilcoxon matched-pairs signed rank test, p = 0.016). d All animals tested showed an increase in the maximum OB-plPFC cross-correlation value from non-freezing to freezing periods (0.34 ± 0. 04 to 0.75 ± 0.07, n = 8, paired two-tailed Student’s t test t(7) = 5.75, p < 0.001). The LFPs were filtered at 2–6 Hz. e Circular distribution of phase differences between OB and plPFC 2–6 Hz signals during freezing. The mean direction of the distribution is 13.5° (red line, with lower 95% confidence limit = 13.0 and upper 95% confidence limit = 14.0, p < 0.001 in one-sample test for mean angle equal to 0°). The phase difference distribution is also visualized as a radial histogram (30 bins) surrounding the polar plot
