Exteroceptive suppression of activity of the temporal muscle in analysis of pain mechanisms

Abstract

Stimulating afferent fibers of the trigeminal nerve usually causes two successive suppressions (ES1 and ES2) of the voluntary muscle activity of chewing muscles. The first phase of decreased voluntary activity is called the early exteroceptive suppression period (ES1); the second phase is called the late exteroceptive suppression period (ES2). Between these two suppression periods is a phase of increased muscle activity, the so-called facilitation period (FP). Usually, in healthy subjects this normal pattern of exteroceptive suppression can be elicited regularly. The reflex answer may occur at low non-painful stimulus intensities; however, typically it appears to be most pronounced with high-intensity stimuli. Because of the obvious relationship between stimulus intensity, pain perception and reflex answer, the reflex is regarded as an antinociceptive reaction. Chronic pain syndromes like chronic tension-type headache and migraine without aura cause changes within the normal ES recording pattern. Furthermore, some substances used in pain therapy such as serotoninagonists or antagonists, acetylsalicylic acid or naloxon may also alter the general appearance of the ES. In this review different parameters that influence the ES reflex answer are summarized. Above, the diagnostic value of the changes of the ES for pathophysiological procedures regarding pain perception and pain processing in certain pain diseases is discussed.