[Reset of masticatory rhythm evoked by stimulation of the cortical masticatory area]

The rhythmical jaw movement can be evoked by repetitive electrical stimulation of the cortical masticatory area in various animals. However, the relationship between evoked jaw movement and each stimulus pulse applied to the cortical masticatory area has not been clarified. The present study examined the effects of each stimulus pulse for evoked masticatory rhythm in urethan anesthetized rabbits. The repetitive electrical stimulation applied to the cortical masticatory area not only evoked rhythmic jaw movement but reset the rhythmic cycle. The application of stimulus pulses till about 70 msec after starting point of the cycle in 4.1 Hz stimulation and till 50 msec in 8.2 Hz stimulation did not reset the cycle length. After these non resetting time, the first stimulus pulse reset the cycle length, and the following any stimulus pulse did not reset the cycle length. When the stimulus pulse reset the cycle length, the length from the applied point of stimulus to the end of cycle was stable: about 184 msec in 4.1 Hz stimulation and 199 msec in 8.2 Hz stimulation. Therefore, the length of basic cycle would be about 250 msec (184 msec + 70 msec = 254 msec in 4.1 Hz stimulation, 199 msec + 50 msec = 249 msec in 8.2 Hz stimulation). This basic cycle length coincided with the shortest cycle length of the rhythmical jaw movement evoked by the most effective stimulation of the cortical masticatory area.