Modulation of mechanically evoked perioral reflexes during active force.

Mechanically evoked activity in orbicularis oris inferior and mentalis muscles was studied in humans during active lip force generation. A specially designed multipoint array skin contactor, coupled to a position servo-controlled linear motor, was used to deliver precise mechanical imputs to the lip vermilion. The array size of the skin contactor was systematically varied to quantify the effects of spatial summation on the amplitude and time course of the early component (R1) of the perioral reflex. For normal young adults, significant positive trends were found for the amplitude of R1 sampled from orbicularis oris inferior and mentalis muscle recording sites as contactor array size increased. Increasing skin contactor size from 2 to 16 points was also effective in shortening the latency of R1 by 3-5 ms.