Development of Chewing in Children from 12 to 48 Months: A Longitudinal Study of EMG Patterns. Jordan R. Green, Christopher A. Moore, Jacki L. Ruark, Paula R. Rodda, Wendy T. Morve, and Marcus J. VanWitzenburg. Department of Speech and Hearing Sciences, University of Washington, Seattle, Washington, Department of Audiology and Speech Pathology, University of Tennessee, Knoxville, Tennessee.
APStracts 4:0048N, 1997.
ABSTRACT
Developmental changes in the coordinative organization of masticatory muscles were examined longitudinally in four children over 49 experimental sessions spanning the age range of 12 to 48 months. Electromyographic (EMG) records were obtained for right and left masseter muscles (RMass and LMass, respectively), right and left temporalis muscles (RTemp and LTemp, respectively), and the anterior belly of the digastric (ABD). Two independent analytic processes were employed, one that relied on identification of onset and offset of muscle activation, and a second that used pairwise crosscorrelational techniques (Moore 1993). The results of these two analyses, which were found to be consistent with each other, demonstrated that the basic chewing pattern of reciprocally activated antagonistic muscle groups is established by 12 months of age. Nevertheless, chewing efficiency appears to be improved through a variety of changes in the chewing pattern throughout early development. Coupling of activity among the jaw elevator muscles was shown to strengthen with maturation, and the synchrony of onset and offset of these muscles also increased. Coactivation of antagonistic muscles decreased significantly with development. This decrease in antagonistic coactivation, increase in synchrony among jaw elevators, and a parallel decrease in EMG burst duration were taken as evidence of increased chewing efficiency. No significant differences in the frequency of chewing were found across the ages studied. Additional considerations include the appropriateness of this coordinative infrastructure for other developing oromotor skills, such as speech production. It is suggested that the relatively fixed coordinative framework for chewing exhibited by these children would not be suitable for adaptation to speech movements, which have been shown to rely on a much more variable and adjustable coordinative organization (Moore 1996). 

Received 25 October 1996; accepted in final form 14 January 1997.
APS Manuscript Number J850-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 5 February 1997