Figure 3.

Sniffing behavior. (a) Example of sniffing behavior. Left: video frame of the rat sniffing while staying in place. Right: respiration (intranasal pressure, a.u.) and frontwards (A _front) and upwards (A _up) head acceleration. The falling phase of the A _front cycle matches with head approach, while the rising phase matches head withdrawals. This is consistent with acceleration being the derivative of velocity. The rat did not vocalize during this period. Dashed lines mark the time of exhalation peaks. (b) Joint distribution of mean respiratory rate and head acceleration rate for each sniffing episode with marginal distributions on the sides (in (b)–(e), top is A _front and bottom is A _up). Warm colors represent highest concentration of values (see color gradient in (c)). Dashed line follows the diagonal. Gray shading in the acceleration marginal distribution represents the cases included in the analysis in (c)–(e). (c) Alignment of respiration to all acceleration peaks detected in the analyzed sniffing episodes. Each row corresponds to a different cycle, sorted from top to bottom by acceleration cycle duration. Dashed lines mark the beginning and end of each acceleration cycle. (d) Phase locking of the respiratory cycle to the acceleration peaks. (e) Phase locking of the acceleration cycle to the peak of exhalation. As a guide for interpreting phase plots, the top panel in (d) shows that, at the times of A _front peaks, respiration was typically transitioning from the peak of exhalation to the peak of inhalation, with a PLV of 0.29, while top panel in (e) shows that at the times of peak exhalation A _front was typically on its rising phase with a PLV of 0.24.