Conditioning of heteronymous H reflex in human temporalis muscle by stimulation of perioral afferents.
A heteronymous H reflex in the temporalis muscle can be elicited by selective stimulation of the masseteric nerve. The present study aimed at defining the optimal amplitude of the H reflex to detect inhibitory changes induced by stimulation of the perioral afferents and at providing new information on the control of masticatory muscles. Sixteen healthy volunteers participated in the experiment. A conditioning stimulus (CS) to the perioral skin was applied at various delays before an ipsilateral selective masseteric nerve stimulation (test stimulus: TS) while the subject was clenching the teeth at 25% of the maximal voluntary contraction. Two intensities of CS and TS were employed, high and low. The peak-to-peak amplitude of the H reflex (TS) and the root-mean-square value of the preceding electromyography were measured and the data analyzed by three-way analysis of variance and Tukey's posthoc tests. For both intensities used the heteronymous H reflex in the temporalis muscle was significantly decreased by prior activation of perioral afferents for delays from 5 to 60 ms. With a delay of 5 and 35 ms the preceding EMG level was not changed, while it was reduced at 20 and 60 ms delay. The intensities used to elicit the heteronymous H reflex of the temporalis muscle were appropriate to detect a reduction in motoneuron excitability. The reduction in the H reflex without a change in the preceding EMG at 5 and 35 ms delays could be due to presynaptic inhibition of the masseteric afferents exerted by the ipsilateral perioral afferents.
Macaluso
G M
GM
Istituto di Clinica Odontoiatrica, Università degli Studi di Parma, Italy.
Graven-Nielsen
T
T
Svensson
P
P
D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D000704:Analysis of Variance; D003213:Conditioning, Psychological / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D013703:Temporal Muscle / Q000502:physiology*