REEVALUATION OF REFLEX RESPONSES OF THE HUMAN MASSETER MUSCLE TO ELECTRICAL LIP STIMULATION

We examined the reflex response of the human masseter muscle to electrical stimulation of the lip using both single motor unit and surface electromyogram based methods. Using the classical analysis methods, reflex response to mild electrical stimuli generated two distinct short-lasting inhibitions. This pattern may reflect the development of combinations of short and long latency inhibitory postsynaptic potentials as a result of the mildly painful electrical lip stimulation. However, this pattern appearing in the classical analysis methods may have developed as a consequence of earlier responses and may not be genuine. This study examined the genuineness of these responses using both the classical analysis methods and the discharge rate method to uncover the realistic postsynaptic potentials in human trigeminal motor nucleus. Using the discharge rate method, we found that the electrical lip stimulation only generated a long-lasting single or compound inhibitory response which is followed by late long-lasting excitation. These findings have important implications on the re-drawing the neuronal pathways of the trigeminal nerve that are frequently used to judge neuromuscular disorders of the trigeminal region.

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