Abstract
To investigate the cause of the jaw motor dysfunctions in patients with cerebral palsy (CP), we compared the reaction times in the CP patients and healthy subjects for the simple reaction-time for the jaw opening motor task. Six CP patients and 6 normal adults participated as subjects. They were instucted to open their jaws as quickly as possible in response to the visual stimulus (S 2) following the sound stimulus (S 1) for the task. A mandibular kinesiogram was applied to record jaw movements. Bipolar surface electromyograms (EMGs) were recorded from the right digastric muscles to observe the agonist muscle activity during jaw opening and right masseter muscle activity during jaw opening. Based on the difference between the EMG and jaw responses, the reaction time was fractioned into the premotor time (PMT) which was the period from the signal to the onset of muscle activity, and the motor time (MT) which was from the onset of muscle activity to the start of movment. Both PMT and MT were significantly longer in the CP patients than in the healthy subjects (p < 0.05). Our results suggest that CP patients have problems in both the processes of the motor preparation for jaw movements.
