A study in the strategy for motor control of human masticatory system - about the participation of anticipation -

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Five elderly dentulous people (mean age 72), three elderly edentulous people with dentures (65), nine dentulous young adults (25), nine dentulous young adults instructed dual-task (24), performed jaw-tapping movements in time to an acoustic signal train with random intervals, that 1.3 Hz interval appears the most frequently. The dual-task group was instructed to memorize words on the monitor screen while performing jaw tapping. We observed some parameters among Masseteric muscle EMG (Mm), Mandibular Kinegiogram, and acoustic signal on surplus tappings. 1. Incidences of surplus tapping in the dual-task group have no relation to numbers of 1.3 Hz repetition and were very low after intervals of 1.3 Hz x 2. Gape in dual-task group is small. 2. The surplus tapping after the interval of 1.3 Hz x 2 appear at intervals of 1.3 Hz from the preceding signal, and began to appear after some 1.3 Hz x 2 intervals. 3. The time lags between the expected signal at intervals of 1.3 HZ from the preceding signal and Mm burst onset of the surplus taping: Those average is smaller at the surplus tapping after 1.3 Hz intervals. (We guess that onset of Mm burst is before the confirmation of signal.) Those average is larger at the surplus tapping after 1.3 Hz x 2 intervals. (We guess that Mm burst onset in both elderly group begin after confirmation of signal.) 4. The more numbers of 1.3 HZ repetition is, the larger gape is except dual-task group. 5. The elderly group have more complete surplus tapping and the young group more incomplete surplus tapping. 6. It can be summarized as follows: In the dual-task group, the second task is not a distracted attention task but an arousal task. Subjects remember intervals that appear the most frequently, the surplus tapping appear at those intervals. And these show the degree of dependence on anticipation.