[Electromyographic study of mentalis muscle reaction to pain].

Three types of muscular reaction to pain were distinguished. Type I--a defensive reaction to a noxious stimulus, type II--muscular guarding at the site of pain, type III--suffering expression. The third type includes reaction of facial muscles discernible only at high pain intensity in subjects with hypersensitivity to pain. In a search for this reaction in all pains electromyographic investigations of the mentalis muscle were carried out since their connection with nociceptive stimulation is made use of in the sign of Marinesco-Radovici. In 18 out of 20 patients with sciatic pain spontaneous activity was observed in the mentalis muscle. Intensification of pain caused by nerve stretching (straight-leg-raising test) evoked activity of these muscles in all studied patients and its intensity was higher. The observed reaction may be an objective evidence of suffering.