Rhythmic breathing adapts to external beat through 'brain...(tune it out if its not going to kill you...)

In mammals, nonassociative learning also involves a secondary form of habituation, called desensitization. Desensitization engages memory to record the habituation and then apply it more generally using a different, surrogate pathway, says Poon.

A study of respiratory rhythms first exposed desensitization as a type of nonassociative learning. If you take a deep breath, says Poon, filling his lungs, the Hering-Breuer reflex tells you not to breathe in anymore. Its time to relax and expire. But if a mechanical respirator is keeping a patients lungs artificially inflated with continual air pressure, a common therapy for patients with sleep apnea or in critical care to keep their lungs and airways open, it is also preventing the patient from breathing out. Meanwhile, the brain is keeping the patient from inhaling. The result of this deadlock is respiratory arrest.

After a moment, however, habituation and desensitization kick in. The vagus nerve, which detects when the lungs are full, habituates to the full signal. At the same time, says Poon, the pneumotaxic center of the pons, the region of the brain that controls rhythmic breathing, counterbalances the Hering-Breuer reflex by zeroing out its relevant neural receptors. As a result, breathing resumes and begins to synchronize with the imposed rhythm of the respirator.

In tests of rats under artificial respiration, Poon found that, if using a suitable rhythm, rats adapted to the mechanical ventilation. Severing the vagus nerve, the nerve supporting habituation, eliminated their ability to adapt. Lesions in the pons, the region supporting desensitization, impaired adaptation.

Poon also found that this learning capability enabled mice to adapt to an artificial rhythm even when the mechanical respirators applied constant air pressure. The rats effectively tuned out this extra pressure, filtering it out as background noise.'/>"/>