Abstract
Electrical stimuli were delivered to the skin over the infraorbital foramen to elicit reflex action potentials in m. orbicularis oris superior (OOS). These short latency responses (10–15 msec poststimulus) are designated as the first perioral reflex component (R1) and appear to be mediated by the brain stem, probably involving two synapses. In this experiment, R1 potentials were elicited under three OOS contraction conditions: (1) with OOS passive, (2) during OOS bursts associated with labial closure for production of [p] in [pa], and (3) during the OOS shutdown with labial opening for the production of [a] in [pa]. The R1s elicited during labial closure had larger amplitudes than those elicited in the passive condition. Conversely, the R1s elicited during labial opening were smaller than those elicited in the passive condition. One interpretation of these findings is that during lip movement excitatory influence of afferents on bulbar motoneurons are modulated by suprebulbar mechanisms. From this perspective, periorial reflex techniques may hold considerable potential for understanding bulbar-suprabulbar interactions during speech production. [Supported by NINDS grants NS-09627 and NS-11780.]
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