Journal of psychophysiology vol:11 issue:3 pages:256-262
The present study investigated whether the EMG activity over two facial muscle regions is sensitive to painful heat. Both the activity over the M. corrugator supercilii (involved in frowning) and over the M. orbicularis oculi region (used in closing the eyelids and tightening the skin around the eye) were recorded in 24 healthy volunteers experiencing painful and non-painful heat stimuli on the hand. The results support the notion that facial EMG responses can be employed to identify defensive activity in response to intense heat stimuli (47 degrees C and 49 degrees C). Both activity over the orbicularis oculi region and over the corrugator region proved (1) to have a high response threshold and (2) to differentiate between low, non-aversive thermal stimuli and high, painful thermal stimuli. However, only the orbicularis oculi activity was sensitive to different levels of painful stimulation.