Fig. 1
During fear retrieval, mice breathe at a characteristic frequency (between 2–6 Hz) while freezing. a Top: The full time course of a retrieval session for a single mouse 24 h after fear conditioning to pure tones. Freezing periods are especially prominent after tone presentations, but also happen during inter-stimulus intervals. Bottom left: quantification of freezing behavior for 8 mice expressed as a percentage of time spent freezing in the 60 s period after each tone presentation. The pre-tone freezing is measured in the 60 s period before the first tone. Bottom right: total freezing time in seconds before (pre-tone) and after (post-tone) the first tone onset. b Power spectral density of the thermocouple (downward deflections represent inhalation, applying to all respiration traces) and OB LFP recordings from a single mouse during non-freezing (from the pre-tone baseline, top) and freezing (bottom) periods. Insets show simulatneously recorded, unfiltered thermocoulple and OB LFP signals. c The instananeous respiratory frequency aligned to a freezing period from each mouse. Top: A raw thermocouple trace from an example mouse (Mouse 8). Bottom: The instantaneous (cycle-to-cycle) frequency of either thermocouple signals or low-pass filtered OB LFPs aligned to the onset of a single freezing period (onset at 5 s). d The respiratory frequency of each mouse during continuous freezing episodes longer than 5 s, estimated by the peaks in the power spectrum of either thermocouple signals or low-pass filtered OB LFPs. The overall average for all mice is 4.05 ± 0.13 Hz (indicated by the dashed line). e The percent power in the 2–6 Hz band during non-freezing baseline as compared to freezing periods (51.20 ± 3.22 to 73.23 ± 2.13, n = 8 paired two-tailed Student’s t test t(7) = 9.67, p < 0.001)
