The Masseter Inhibitory Reflex in Pontine Lesions
A variety of stimuli anywhere within the mouth or on the facial skin of the maxillary or mandibular trigeminal division evoke bilateral inhibitory reflex responses in jaw-closing muscles. One of these reflexes is the masseter inhibitory reflex (MIR) [1–3], which consists of early (SP1)and late (SP2) phases of an electrical silent period in masseter voluntary activity (Fig. 1A). Characteristics of the two reflex components are standardized by giving a reflex threshold electrical stimulus three times to the mental nerve at the chin during maximal clenching of the jaws (Fig. 2). It may be necessary to use a concentric needle electrode instead of surface electrodes, particularly if the signal is contaminated by facial muscle activity. Maximal contraction has to be maintained for not more than 3 s with the aid of audiovisual feedback by the EMG apparatus. After relaxation, contraction is repeated every 30s to avoid disappearance of EMG activity between the two silences.
KeywordsTrigeminal Neuralgia magnetiC Resonance Image Lesion Mental Nerve Cutaneous Silent Period Pontine Lesion
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