EXTEROCEPTIVE SUPPRESSION OF TEMPORALIS M USCLE-ACTIVITY - PRINCIPLESAND APPLICATION

The exteroceptive suppression period (ES) of the temporalis muscle act ivity is a trigemino-trigeminal brain stem reflex. It will be elicited most when stimulating trigeminal sensory afferents by painful stimuli and typically leads to a biphasic interruption of voluntary muscle ac tivity. The first phase of decreased voluntary activity is called the early exteroceptive suppression period (ES1), the second, the late ext eroceptive suppression period (ES2). Between these two suppression per iods a phase of increased muscle activity, the so-called facilitation period (FP), can be seen. This phenomenon can be modulated by differen t stimulating parameters and usually, in healthy subjects, this normal pattern of the exteroceptive suppression can be elicited regularly. T he reflex answer may occur at low non-painful stimulus intensities; ty pically, however, it appears to be most pronounced with high-intensity stimuli. Because of the obvious relationship between stimulus intensi ty, pain perception and reflex, the reflex is regarded as an antinocic eptive reaction. The absence of an inhibition of motor activity can be visualized, for example, in hemimasticatory spasm or dystonic disorde rs. However, above all the ES nowadays attracts most attention as a to ol to analyse different pain syndromes. One main advantage of this met hod in man is the ability to evaluate certain antinociceptive brain st em mechanisms functionally by means of a simple noninvasive technique. A large number of results have been obtained showing that chronic pai n syndromes such as chronic tension-type headache and migraine cause c hanges within the normal ES recording pattern. Furthermore, some subst ances used in pain therapy, such as serotonin agonists or antagonists, acetylsalicylic acid or naloxone, may also alter the general appearan ce of the ES. This review will summarize different parameters that inf luence the ES reflex answer. Furthermore, the diagnostic value of chan ges in the ES for pathophysiological processes regarding pain percepti on and processing in certain painsyndromes will be discussed.