Spectral analysis of the electromyogram of the temporal muscle in the rhesus monkey (Macaca mulatta).

Spontaneous EMG activity of one mandibular elevator and postural muscle, the anterior temporalis, was recorded from 20 unanesthetized rhesus monkeys subjected to 4 experimental protocols. The EMG activity was analyzed with a spectral analyzer to determine changes in particular frequency bandwidths after (1) administering a dissociative drug, (2) placing weights on the mandible, (3) detaching the muscle, and (4) adaptation of the muscle to oral respiration. The mean distribution of frequency components indicated that ketamine--HCl increased the power of all frequencies below 400 c/sec, particularly those at 20--40 c/sec. A period of hyperactivity and increased recruitment and discharge of motor units occurred within the first 30 min following administration of the drug. Passive and sustained lowering of the jaw with increased weights indicated that increasing the front incisor distance 2--4 cm significantly decreased the frequency components below 400 c/sec accompanying a decrease in active motor units. Comparison of frequency components of the temporalis EMG before and within 40 days after detachment suggested some subtle variations in the mean distributions predominantly around 200 c/sec but without significant changes. Comparison of the mean spectral distribution between 8 nasal-breathing and 8 oral-breathing monkeys indicated a significant loss of power in the normal dominant frequency range of 20--100 c/sec in the oral respiratory group except for enhancement of the 20 c/sec bandwidth. The results suggest that the anterior temporalis alters its EMG activity during both short (i.e., min, h) and long-term (i.e., months, year) adaptations of the muscle.