Modulation of the mechanically evoked perioral reflex during active force dynamics in young adults.

Mechanically evoked reflex activity in the superior and inferior segments of the orbicularis oris muscle was sampled from three normal females using a specially designed linear motor operating under force feedback. Mechanical inputs delivered to the left upper lip during a ramp-and-hold task produced a composite reflex response characterized by phases of excitation and suppression at the homonymous muscle recording site. The modulation of the evoked composite perioral reflex was found to be dependent upon the rate and phase of force recruitment. The organization of the composite perioral reflex response is discussed in relation to speech motor control and load compensatory mechanisms.