The VRG contains both inspiratory and expiratory neurons. The VRG is secondarily responsible for initiation of inspiratory activity, after the dorsal respiratory group. The nucleus para-ambiguus is active during inspiration, while the nucleus retrofacialis and the nucleus retroambiguus are active during exhalation.
The VRG is responsible for motor control of inspiratory and expiratory muscles during exercise.
The pre-Bötzinger complex is the hypothesized location of central respiratory rhythm pattern generation circuitry. The pre-botzinger complex also contains pacemaker cells which initiate spontaneous breathing. It is currently unclear how this system regulates its output to effect motoneuron bursting, which in turn is responsible for inspiratory muscle innervation. Research into the function of the pre-Bötzinger complex is currently being studied by making use of the in vitro slice preparation.