The aim of this study was to demonstrate that silent periods of the mentalis muscle are induced after facial nerve stimulation and cutaneous stimulation in normal subjects. When the marginal mandibular branch of the facial nerve and the cutaneous nerve in areas adjacent to the lower lip were stimulated during slight voluntary contraction of the mentalis muscle, silent periods were elicited with surface electrodes on the mentalis muscle. The early phase and the late phase of the silent period were elicited by marginal mandibular branch stimulation. The early phase of the silent period was recognized following the F waves and it disappeared at 36.3 msec. The average duration of the late phase of the silent period was 59.2 msec, with an average latency of 62.5 msec. Only the late phase of the silent period after cutaneous stimulation could be elicited, with a duration and latency of 55.9 msec and 54.0 msec respectively. The authors conclude that the silent period is able to be elicited in the mentalis muscle by peripheral nerve stimulation, and is one of the late responses in facial muscles.
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