[Modulation of the jaw muscle activity during the rhythmical jaw movement by stimulation of the cortical masticatory area and amygdala in the rabbit].

The effect of each stimulus pulse to the digastric and masseter muscles activities was examined during the rhythmic jaw movement evoked by repetitive electrical stimulation of the cortical masticatory area and amygdala in the rabbit. The stimulus pulse evoked facilitation and suppression in the digastric muscle activity, and suppression and slight facilitation in the masseter muscle activity. No obvious difference in the pattern of the modulation was appeared between the stimulation of the anterior and posterior cortical masticatory area in the digastric muscle activity. In masseter muscle, the stimulation of the anterior cortical masticatory area showed remarkable suppression only, whereas the stimulation of the posterior cortical masticatory area evoked both suppression and facilitation. Lager motor units were received conspicuous modulation than smaller motor units in both muscles. The time course of these modulation was resembled with those of the masseteric and digastric reflexes by stimulation of the cortical masticatory area. We concluded that the modulation evoked by repetitive electrical stimulation of the cortical masticatory area might be occurred by stimulation of the same pathway as evoking the modulation of reflexes. The repetitive electrical stimulation of the amygdala induced rhythmical jaw movement. In the digastric and masseter muscles, the stimulus pulse evoked facilitation, whereas no obvious suppression was appeared. Lager motor unit was modulated remarkably than smaller unit.