The early component of the mechanically evoked lip muscle reflexes was
studied in order to determine whether a consistent form of modulation
occurs in associated neural pathways during the preparation to speak.
Electromyograms (EMG) were obtained of upper and lower lip muscle whi
le subjects were presented simultaneously with a visual instruction st
imulus and a mechanical reflex stimulus every 4 s. On alternating tria
ls, they were to produce either a single word or maintain their lip po
sture when they felt the mechanical stimulus. Consistent reductions in
reflex amplitude were observed across subjects in lower lip muscle in
the speech condition compared with the no-response condition. Statist
ical analyses suggest that this suppression effect occurred independen
tly of variations in prestimulus EMG. These results are consistent wit
h the idea that trigeminal sensory pathways innervating the perioral r
egion are suppressed in preparation for orofacial movements associated
with simple speech utterances.