Symmetry of Mandibular Muscle Activity as an Index of Coordinative Strategy Electromyographic activity of bilateral mandibular muscle pairs in humans was studied during several tasks: mastication, voluntary oscillation of the jaw, and speech production, as a replication and extension of an earlier investigation by Moore, Smith, and Ringel (1988). The synchrony of activity within and across these paired muscles (masseter, medial ... Research Article
Research Article  |   December 01, 1993
Symmetry of Mandibular Muscle Activity as an Index of Coordinative Strategy
 
Author Affiliations & Notes
  • Christopher A. Moore
    University of Pittsburgh
  • Contact author: Christopher A. Moore, PhD, Division of Communication Sciences and Disorders, 1117 Cathedral of Learning, University of Pittsburgh, Pittsburgh, PA 15260. E-mail: CMOORE@VMS.CIS.PITT.EDU
Article Information
Swallowing, Dysphagia & Feeding Disorders / Speech, Voice & Prosody / Speech / Research Articles
Research Article   |   December 01, 1993
Symmetry of Mandibular Muscle Activity as an Index of Coordinative Strategy
Journal of Speech, Language, and Hearing Research, December 1993, Vol. 36, 1145-1157. doi:10.1044/jshr.3606.1145
History: Received February 26, 1993 , Accepted June 21, 1993
 
Journal of Speech, Language, and Hearing Research, December 1993, Vol. 36, 1145-1157. doi:10.1044/jshr.3606.1145
History: Received February 26, 1993; Accepted June 21, 1993

Electromyographic activity of bilateral mandibular muscle pairs in humans was studied during several tasks: mastication, voluntary oscillation of the jaw, and speech production, as a replication and extension of an earlier investigation by Moore, Smith, and Ringel (1988). The synchrony of activity within and across these paired muscles (masseter, medial pterygoid, and the anterior belly of the digastric) was evaluated by statistical comparison of zero-lag crosscorrelation coefficients between all possible pairs. Paired comparisons were classified and combined according to anatomical and biomechanical properties into comparisons of homologous pairs (e.g., synchrony of activity in right masseter with left masseter), ipsilateral synergists (e.g., right masseter with right medial pterygoid), contralateral synergists (e.g., right masseter with left medial pterygoid), ipsilateral antagonists (e.g., right masseter with right digastric), and contralateral antagonists (e.g., right masseter with left digastric). Statistical comparison of the coactivation within muscle groups (across tasks) and across these muscle groups (within tasks) revealed significantly different groups of coactivated groups for each of the three tasks studied. The grouping of these muscles into coactivated groups always included homologous pairs among those most synchronously active. During mastication, homologous pairs and ipsilateral synergists were coactivated to a degree significantly greater than either of the antagonistic groups or the contralateral synergists. During voluntary oscillation of the jaw, coactive muscle groups were shown to be primarily the homologous pairs; synergists were coactivated to a significantly lesser degree, and antagonistic muscles were reciprocally active. During speech production, only homologous pairs emerged as a highly coactive group, although synergists and antagonistic pairs were coactive to a lesser degree. This finding was interpreted as a further indication of the coordinative plasticity among mandibular muscles, and as a demonstration of the vast differences in the apparent coordinative strategies for speech and nonspeech tasks. Speculation regarding the root of these differences is focused on the differences in kinematic and force-generating requirements of each task.

Acknowledgments
The author wishes to acknowledge the efforts in support of this investigation by Margaret Denny, Janine Janosky, Erich Luschei, Angela Rahn, Jacki Ruark, and Anne Smith. Support was provided by a grant from the NIDCD (DC00822).
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