[Facilitation of tibialis anterior H reflex and depression of reciprocal Ia inhibition on soleus motoneurons during teeth-clenching in man].

Modulation of the tibialis anterior (T.A.) H reflex and the reciprocal Ia inhibition from the ankle flexor to the extensor were studied during voluntary teeth-clenching in 7 healthy adult volunteers to investigate the correlation between the oral motor activity and the somatic motor function. The T.A. H reflex was significantly facilitated during voluntary teeth-clenching, and the amount of this facilitation increased with the level of masseter EMG activity. Furthermore, the reciprocal Ia inhibition of the soleus H reflex, induced by stimulation of the common peroneal nerve at a subthreshold intensity for evoking the T.A. M wave, was significantly depressed during voluntary teeth-clenching. It was concluded that 1) the T.A. H reflex is facilitated during voluntary teeth-clenching, 2) there is a positive correlation between the amount of facilitation of the T.A. H reflex and the level of teeth-clenching force, and 3) the reciprocal Ia inhibition of the crural muscle is reduced during voluntary teeth-clenching. It was suggested that teeth-clenching contributes to stability of body stance by increasing the stiffness of the ankle joint.