Peri-oral reflexes in the conscious monkey (Macaca Mulatta)

Three rhesus monkeys were trained to exert simultaneous forces with their jaws and lips against force transducers. The lip transducer was coupled to a servocontrolled electro-magnet stimulator. Electromyographic (EMG) activity was recorded from orbicularis oris (OOS) and medial pterygoid (MPT) muscles. Elevation or depression of the lip-force transducer with the electromagnet elicited reflexes in the lip- and jaw-closing muscles. Reflex amplitudes elicited by stretching the OOS were logarithmically related to stimulus velocity. Depression of the lip-force transducer released pre-existing stretch of the OOS muscle and elicited reflexes in the OOS and MPT. The amplitudes of the reflexes elicited by the release stimuli were slightly greater than those elicited by stretching the lip. There was no short latency suppression of the OOS EMG following the release stimulus. The perioral reflex of the macaque appears to be similar to that of man; there appear to be no normal-acting muscle spindles in the OOS muscle.