henry copeland:

Animal study connects fear behavior, rhythmic breathing, brain smell center -- ScienceDaily

Other groups have observed that the amygdala and prelimbic prefrontal cortex, which govern learning and memory, emotion, and decision-making, were electrically active during "freezing," at an average of 4 Hz. Moberly observed that freeze behavior, breathing rate, and electrical activity of these brain regions were coordinated literally on the same wavelength.
- www.sciencedaily.com