Neurogenesis of respiratory rhythm and pattern: emerging concepts.

We present three hypotheses related to the nervous system control of breathing in mammals: 1) that neural mechanisms controlling breathing change with state and that the relationship between mechanisms in different states can be described in terms of either modulation or a basic transformation of properties, or both; 2) that the mechanisms generating respiratory rhythm and pattern are separate; and 3) that conditional pacemaker cell activity is the basis for respiratory rhythm in highly reduced states.