Comparison of perioral reflex modulation in the upper and lower lip.

The spatiotemporal organization and specificity of the mechanically evoked, short latency perioral response (R1) was sampled from a group of normal adult humans. Perioral reflex activity was sampled during passive and active static force conditions in the presence of servo-controlled mechanical inputs to lip vermilion. Results confirmed that the sensorimotor apparatus of the lower face is very responsive to low level mechanical inputs and highly dependent on several factors including input site (upper vs. lower lip), amount of glabrous tissue stimulated (contactor array size), and task dynamics (passive vs. active subject-generated lip force). Arguments are presented to support the idea that several features of the peripheral sensory environment encoded by primary trigeminal afferents, including afferent gain, specificity, locus, and spatial summation, collectively provide inputs vital to higher order sensory relays in the development of a central representation and dynamic conformational map of perioral space. These sensorimotor features encoded by trigeminal afferents are presumed important for motor learning and maintenance of oromotor control during speech, suck, mastication and swallow, and gesture.