Modulation of mechanically evoked perioral reflexes during active force

Area of Science:

• Neuroscience
• Biomechanics
• Human motor control

Background:

• The perioral reflex is a crucial protective mechanism.
• Understanding the factors influencing this reflex, such as mechanical input, is important for assessing lip function.

Purpose of the Study:

• To investigate the effect of mechanical stimulation area on the perioral reflex (R1) in human lip muscles.
• To quantify the relationship between spatial summation and reflex amplitude and latency.

Main Methods:

• Utilized a servo-controlled linear motor with a multipoint array skin contactor to apply precise mechanical stimuli to the lip vermilion.
• Systematically varied the contactor array size to assess spatial summation effects.
• Recorded electromyographic activity from the orbicularis oris inferior and mentalis muscles.

Main Results:

• A significant positive correlation was observed between the contactor array size and the amplitude of the R1 component of the perioral reflex.
• Increasing the contactor size from 2 to 16 points resulted in a 3-5 ms reduction in the R1 latency.
• These findings were consistent across both orbicularis oris inferior and mentalis muscle recordings.

Conclusions:

• The size of the mechanical stimulus applied to the lip vermilion directly influences the amplitude and latency of the early perioral reflex (R1).
• Spatial summation plays a significant role in modulating the perioral reflex response.
• These results provide quantitative insights into the sensory-motor control of lip function.