Mentalis Muscle Responses to Median Nerve Stimulation

Kwong-Kum Liao；Jen-Tse Chen；Kuan-Lin Lai；Chuen-Der Kao；Chia-Yi Lin；Chih-Yang Liu；Yung-Yang Lin；Din-E Shan；Zin-An Wu

brainstem ； median nerve ； mentalis ； long loop reflex

The Chinese Journal of Physiology

49卷4期（2006 / 08 / 31）

174 - 181

英文

Electrical stimulation may produce excitation or inhibition of the motor neurons, as represented the blink reflex and masseter silent period in response to trigeminal nerve stimulation. Clinically, a light touch on the palm may evoke a mentalis muscle response (MMR), i.e. a palmomental reflex. In this study, we attempted to characterize the MMR to median nerve stimulation. Electrical stimulation was applied at the median nerve with recordings at the mentalis muscles. An inhibition study was done with continuous stimuli during muscle contraction (Ⅰ1 and Ⅰ2 of MMR(subscript average)). Excitation was done with a single shot during muscle relaxation (MMR(subscript single)) or by continuous stimuli during muscle contraction (E1 and E2 of MMR(subscript average)). The characteristic differences between MMR(subscript average) and MMR(subscript single) were as follows: earlier onset latencies of MMR(subscript average) (MMR(subscript average)＜45 ms; MMR(subscript single)＞60 ms), and a lower amplitude of MMR(subscript average) (MMR(subscript average)＜50 μV; MMR(subscript single)＞150 μV). The receptive field of MMR(subscript single) was widespread over the body surface and that of MMR(subscript average) was limited to the trigeminal, median and index digital nerves. Series of stimuli usually significantly decreased the amplitude of MMR(subscript single), as a phenomenon of habituation. On the other hand, it was difficult to evoke the earlier response (i.e. MMR(subscript average)) without continuous stimuli and an average technique. MMR(subscript average) had the components of both excitation (E) and inhibition (I); for example, E1-Ⅰ1-E2-Ⅰ2 or Ⅰ1-E2-Ⅰ2. E2 was the most consistent component. In patients with dorsal column dysfunction, median nerve stimulation could successfully elicit MMR(subscript single), but not MMR(subscript average). Contrarily, in patients with pain sensory loss, it was more difficult to reproduce MMR(subscript single) than MMR(subscript average). It seemed that MMR(subscript average) and MMR(subscript single) did not have equivalents across the different modalities of stimulation.

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