Spinal motoneurons of the human newborn are highly synchronized during leg movements

Motoneurons of neonatal rodents show synchronous activity that modulates the development of the neuromuscular
system. However, the characteristics of the activity of human neonatal motoneurons are largely unknown. Using
a noninvasive neural interface, we identified the discharge timings of individual spinal motoneurons in human
newborns. We found highly synchronized activities of motoneurons of the tibialis anterior muscle, which were
associated with fast leg movements. Although neonates’ motor units exhibited discharge rates similar to those of
adults, their synchronization was significantly greater than in adults. Moreover, neonatal motor units showed
coherent oscillations in the delta band, which is directly translated into force generation. These results suggest
that motoneuron synchronization in human neonates might be an important mechanism for controlling fast limb
movements, such as those of primitive reflexes. In addition to help revealing mechanisms of development, the
proposed neural interface might monitor children at risk of developing motor disorders.