Comment: gating effects and constraints on the central pattern generators for rhythmic movements.

Respiration, mastication, and locomotion are compared in terms of the contributions of events occurring at the motoneuron membrane and at premotoneuronal levels for the production of phasic gain changes of afferent effects. Data are presented which suggest that an inhibitory mechanism operating on limb motoneurons can prevent disruption of the locomotor pattern by proprioceptive input and that Ia inhibitory interneurons contribute to this rhythmic inhibition of both flexor and extensor motoneurons. Renshaw cell rhythmic activity during locomotion is described and discussed in terms of its possible role in gating of inputs to motoneurons.