| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1991: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1990: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Freely moving rabbits were stailied 1) to identify jaw behaviors on the basis of jaw movement trajectories and masticatory muscle activities, and 2) to observe influences of the head fixation on jaw behaviors during hard or soft food chewing. Jaw movements were traced usins a magnet-magnetic sensing system. The jaw tracking system consisted of two magnet sensors fixed on the animal's head and a small magnet fixed in the mandible. Additional sensor was set on the head to pick up the earth's ugnetiss so that the head movements could be recorded. Muscle. activities were induced using bipolar electrodes made of silver, which were implanted under the skin. The target included bilateral superficial m=ter and digastric muscles, unilateral deep reasseter, medial pterygoid, sylohyoid, sternohyoid, thyrohyoid muscles. EEG was induced using pin electrodes screwed into the skull bone. All the signals were conveyed to a connector pedestal under the skin and fed into a recording system by flexible c
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ables. For recording animals were placed in a cage (70 cm X 70 cm). It began at least four days after the operations. In a period of awaking, three rhythmical and characteristic jaw behaviors including chewing, drinking and grooming behavior were recognized in the recordings. In a period of sleeping, short EMG bursts similar to clenching or grindins were recorded in the closing muscles. The basic pattern in the chewing movements recorded from freely moving rabbits was identical to those of the animals their heads fixed. Grooming behavior was studied and the body licking was found to be a rhythmical jaw movement with characteristic jaw movements. Hard food and soft food were tested and the results opposed to those observed from animals head fixed. In this study, hard soft was found to have longer cycle time than that of hard food. It is suggested that the opening time should be considered as the determinant of the change in the cycle time. The freely moving rabbits employed here could be a reliable model to study jaw motor system. Less
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