Fig. 4: Stronger 4 Hz power is linked to more sustained and stable freezing episodes.

a OB spectrogram (top) and mean power in the 4 Hz band (bottom) triggered on freezing periods of normalized duration for all mice. Note the asymmetric rise and fall of 4 Hz power during the freezing bout with a gradual onset and steep offset. (n = 15 mice). b, d OB 4 Hz power (b) and head acceleration (d) triggered on onset (left, orange) and offset (right, purple) of freezing bouts. Both measures are normalized between 0 and 1. Black bar indicates the standard deviation at the midpoint. (n = 11, 11 mice, only mice with sufficient number of 4 s bouts of freezing are retained). c, e Slope of onset and offset curves of and OB 4 Hz power (c) head acceleration (e) to quantify the difference in transition speed, estimated using a sigmoid fit. (Wilcoxon rank-sum: zval = −3.61, −0.32; p = 3e−3, 0.74, n = 11). f Density of micromovements during freezing periods of normalized duration showing that they decrease throughout the episode, following a similar dynamic to 4 Hz increase. These small head movements are detectable using head accelerometer only but are not readily visible on video measurements and often coincide with the bips of the CS. (n = 11 mice). Error bars are SEM. g The amplitude of the micromovements elicited by CS pips is correlated with the instantaneous 4 Hz power. (Pearson correlation: R = −0.56, p = 2.3e−54, n = 578 movements from 11 mice). Error bars are SEM. h Averaged OB spectra during short (<10 s) and long (>10 s) freezing periods showing stronger 4 Hz during long episodes. Error bars are SEM. Inset: average signal-to-noise ratio of 3–6 Hz band during short and long episodes. (Paired Wilcoxon signed-rank test: Signed Rank statistic = 0, p = 2.44e−4, n = 13). In all panels, boxplots show median and interquartile range.