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Impact of Rhythmic Oral Activity on the Timing of Muscle Activation in the Swallow of the Decerebrate Pig

¹Division of Physiology, King's College, London, United Kingdom; ²Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts; and ³Department of Physical Medicine and Rehabilitation, Johns Hopkins University, Baltimore, Maryland

Submitted 31 July 2008; accepted in final form 3 December 2008

Abstract

The pharyngeal swallow can be elicited as an isolated event but, in normal animals, it occurs within the context of rhythmic tongue and jaw movement (RTJM). The response includes activation of the multifunctional geniohyoid muscle, which can either protract the hyoid or assist jaw opening; in conscious nonprimate mammals, two bursts of geniohyoid EMG activity (GHemg) occur in swallow cycles at times consistent with these two actions. However, during experimentally elicited pharyngeal swallows, GHemg classically occurs at the same time as hyoglossus and mylohyoid activity (short latency response) but, when the swallow is elicited in the decerebrate in the absence of RTJM, GHemg occurs later in the swallow (long latency response). We tested the hypothesis that it was not influences from higher centers but a brain stem mechanism, associated with RTJM, which caused GHemg to occur earlier in the swallow. In 38 decerebrate piglets, RTJM occurred sporadically in seven animals. Before RTJM, GHemg had a long latency, but, during RTJM, swallow related GHemg occurred synchronously with activity in hyoglossus and mylohyoid, early in the swallow. Both early and late responses were present during the changeover period. During this changeover period, duplicate electrodes in the geniohyoid could individually detect either the early or the late burst in the same swallow. This suggested that two sets of geniohyoid task units existed that were potentially active in the swallow and that they were differentially facilitated or inhibited depending on the presence or absence of rhythmic activity originating in the brain stem.

This article has been cited by other articles:

				R. Z. German, A. W. Crompton, and A. J. Thexton Integration of the Reflex Pharyngeal Swallow Into Rhythmic Oral Activity in a Neurologically Intact Pig Model J Neurophysiol, August 1, 2009; 102(2): 1017 - 1025. [Abstract] [Full Text] [PDF]