Fig. 6. Balance between BLA-mPFC 4 Hz and 8 Hz activity predicts stability of post-extinction freezing.

a Extinction learning reduces the duration, but not frequency, of freezing bouts. Pooled frequency histogram of all freezing bouts across all animals showed a left-shift in distribution, indicating shorter duration but not lower frequency of freezing bouts after extinction (left: n = 36 mice; 0.4 s bins). Comparison of pre- and post-extinction learning shows that while average bout frequency remains unchanged (middle; paired two-tailed t-test: P = 0.19, t(34) = 1.34, n = 35 mice), average bout duration is significantly reduced after extinction (right; paired two-tailed t-test: P < 0.0001, t(34) = 6.34, n = 35 mice). b Correlation between change in 4:8 Hz cross-power ratio with change in average bout duration (post-minus pre-extinction learning; non-parametric Spearman correlation: two-tailed P = 0.058; r = 0.39; n = 24 mice). c Example cross-power spectrogram from individual mouse showing freeze bouts of various lengths. d, e Average cross-power spectrograms (d) and spectra (e) comparing short (2–3.5 s bouts; n = 18 mice) vs. long (>3.5 s; n = 15 mice) freeze bouts during post-extinction retrieval trials. (e inset is quantification as 4:8 Hz cross-power ratio. Unpaired t-test (two-tailed): t(31) = 1.75; P = 0.09; box plot shows median (line inside box), 25% and 75% percentiles (box edges), and minimum and maximum values (error bars). f Correlation between the duration and the cross-power ratio of all freezing bouts (>2 s during no stimulation periods in the post-extinction retrieval trial; non-parametric Spearman correlation: two-tailed P = 0.0002; r = 0.33; 118 bouts from n = 23 mice). Bouts from single example mouse highlighted in blue (linear regression F(1,5) = 99.21, P = 0.0002, R² = 0.95, n = 7 bouts). g Histogram of freezing bouts by duration during 4 Hz vs. 8 Hz stimulation in the conditioned context post-extinction learning (bouts cumulated from n = 25 mice). 4 Hz stimulation leads to an increase in both frequency (middle) and average duration (right) of freezing bouts compared to 8 Hz stimulation (paired two-tailed t-test: frequency: P = 0.0002, t(24) = 4.43; duration: P = 0.016, t(24) = 2.59; n = 25 mice). All error bars and shaded area: mean ± SEM.