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Evaluating the triplet hypothesis during rhythmic mastication in primates
Author(s) -
Yashesvini Ram,
Callum F. Ross
Publication year - 2017
Publication title -
journal of experimental biology
Language(s) - English
Resource type - Journals
eISSN - 1477-9145
pISSN - 0022-0949
DOI - 10.1242/jeb.165985
Subject(s) - mastication , rhythm , neuroscience , biology , communication , psychology , paleontology , medicine
Mammalian mastication involves precise jaw movements including transverse movement of the mandible during the power stroke. Jaw elevation and transverse movement are driven by asymmetrical jaw elevator muscle activity which is thought to include a phylogenetically primitive and conserved triplet motor pattern consisting of: triplet I—balancing side superficial masseter and medial pterygoid, working side posterior temporalis— which reaches onset, peak, and offset first; and triplet II—working side superficial masseter and medial pterygoid, balancing side posterior temporalis—which is active second. Although the presence of a triplet motor pattern has been confirmed in several primate species, the prevalence of this motor pattern—the proportion of cycles that display this pattern—has not been evaluated in primates. The present study quantifies the presence and prevalence of the triplet motor pattern in five different primate species, Eulemur fulvus, Propithecus verreauxi, Papio anubis, Macaca fascicularis, and Pan troglodytes, using mean onset, peak, and offset time relative to working superficial masseter. In all five of the species studied, the mean triplet motor pattern is observed at peak muscle activation, and in four out of the five species the triplet motor pattern occurs more frequently than expected at random at peak muscle activation and offset. Non-triplet motor patterns were observed in varying proportions at different time points in the cycle, suggesting that presence or absence of the triplet motor pattern is not a binomial trait. Instead, the primate masticatory motor pattern is malleable within individual cycles, within individual animals, and therefore within species.

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