Meeting Abstract
Mastication is a complex and variable behavior that is also rhythmic. During mastication, the amplitude and timing of muscle activity demonstrates both stereotypy and flexibility. Current hypotheses suggest that groups of muscles are activated as units (Triplets) during specific phases of the masticatory cycle. The present study examines these claims by quantitatively evaluating the interaction between muscle pairs using Hilbert relative phase. Two muscles are synchronized if their relative phase is constant and events within their cycles occur in unison. Muscle coordination is defined here as modulation (adjustment or maintenance) of relative muscle activity (amplitude and timing) to achieve goal specific force production and kinematics. Two muscles are coordinated if they have low variation in relative phase either within a sequence or between sequences. Preliminary results based on 36 masticatory sequences in a single macaque (Macaca mulatta) show that the triplet muscles (left and right superficial masseters, medial pterygoids, and posterior temporalis) are synchronized within a sequence but not coordinated between sequences. Moreover, within a sequence, muscles in the same triplet have a lower relative phase than muscles in two different triplets. These findings suggest that the jaw closing muscles (especially muscles within the same triplet) are phase locked with each other, but they are also controlled independently.
