Precursor of respiratory pattern in the early gestation mammalian fetus

Recordings of respiratory muscle activity in fetal lambs from early in gestation provide insight into the organization of the central pattern generator for respiration in mammals. Evidence presented here is consistent with the recent hypothesis that production of the respiratory pattern involves two separate neural modules: one, the 'rhythm' module, which specifies the respiratory cycle and another, the 'form' module, which creates the characteristic shape of each burst of activity within this cycle. The rhythm module is already functional when gestation is 35% complete while the form module appears to be constructed gradually over the second half of gestation.