Figure 2. Illustration of triple-oscillator hypothesis.

We propose that, at rest, the preBötzinger complex (preBötC) and post-inspiratory complex (PiCo) alternate activity to generate a two-phase rhythm, inspiration and post-inspiration. Under periods of high metabolic demand, for instance during exercise, a third oscillator is incorporated to create a three-phase rhythm. We propose that each of the three phases – inspiration, post-inspiration, and active expiration – are controlled by independent oscillators: the preBötC, PiCo, and lateral parafacial nucleus (pF _L), respectively. We further postulate that inhibition between these networks coordinates the phasing and timing of the rhythms.