Meeting Abstract

LBS1.5  Thursday, Jan. 3  EMG during Primate Chewing: Patterns and Prospects for Studying Masticatory Function and Evolution VINYARD, C.J.*; WALL, C.E.; NEOUCOM; Duke University cvinyard@neoucom.edu

Mammalian chewing poses major challenges to describing muscle function. In contrast to a locomotor sequence, mammals destroy the substrate (ie, food) as a chewing sequence progresses. The complexity induced by a deteriorating substrate is compounded by the multiple potential muscle combinations for generating bite force and jaw movement. Due to these complexities, researchers rely on in vivo descriptions of jaw-muscle function. EMG is a key tool in this effort. We explore 25 years of methodologically-consistent EMG data on primate chewing published by Hylander et al. at interspecific, intraspecific and intra-sequence levels to assess what EMG data tell us about masticatory function. Comparison of summary EMGs across 10 primate species indicates that jaw-muscle timing and recruitment are correlated with jaw form. This interspecific association suggests that jaw-muscle activity patterns are an integrated and evolving part of the primate masticatory apparatus. At the other extreme, intra-sequence variation in jaw-muscle EMGs are far more complex with significant variation in EMG parameters persisting throughout chewing sequences. Further, intra-sequence complexity differs markedly among species. We speculate that much of this variation relates to changing demands put on the muscles as food properties are systematically altered during a chewing sequence. To begin reconciling these distinct observations, we are combining EMG with sonomicrometry and strain gage analyses to assess muscle strain and relative work during chewing in representative primates. Initial results from capuchins and macaques suggest that EMG parameters only partly capture how jaw muscles alter their mechanics as a function of bite point location, food properties and position in a chewing sequence. Supported by NSF.