Electrophysiological observations on the palmomental reflex in normal neonates.

The authors report normative data on the electrical response (EMG response) recorded from the mentoneal muscles by repetitive mechanical stimulation of the thenar eminence surface of the hand in 18 neonates, 1 to 6 days old: the so-called palmomental reflex (PMR) or palm-chin reflex. PMR potentials showed in most cases great variability in amplitude and duration but not in latency, and they were present in all but one of the cases. The PMR was monolateral in one case only. Evoked potentials from the scalp were also recorded after electrical stimulation of the thenar eminence. The afferent branch of the PMR is constituted of impulses originating mainly from median nerve, skin and muscle receptors. Such impulses may reach facial motor nuclei following corticofugal pathways throughout a long-loop circuit.