Thexton AJ, Crompton AW, German RZ. Electromyographic activity during the reflex pharyngeal swallow in the pig: Doty and Bosma (1956) revisited. The currently accepted description of the pattern of electromyographic (EMG) activity in the pharyngeal swallow is that reported by Doty and Bosma in 1956; however, those authors describe high levels of intramuscle and of interindividual EMG variation. We reinvestigated this pattern, testing two hypotheses concerning EMG variation: 1) that it could be

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... educed with modern methodology and 2) that it could be explained by selective detection of different types of motor units. In eight decerebrate infant pigs, we elicited radiographically verified pharyngeal swallows and recorded EMG activity from a total of 16 muscles. Synchronization signals from the video-radiographic system allowed the EMG activity associated with each swallow to be aligned directly with epiglottal movement. The movements were highly stereotyped, but the recorded EMG signals were variable at both the intramuscle and interanimal level. During swallowing, some muscles subserved multiple functions and contained different task units; there were also intramuscle differences in EMG latencies. In this situation, statistical methods were essential to characterize the overall patterns of EMG activity. The statistically derived multimuscle pattern approximated to the classical description by Doty and Bosma (Doty RW, Bosma JF. J Neurophysiol 19: 44 -60, 1956) with a leading complex of muscle activities. However, the mylohyoid was not active earlier than other muscles, and the geniohyoid muscle was not part of the leading complex. Some muscles, classically considered inactive, were active during the pharyngeal swallow. muscle; motor pattern; electromyogram; deglutition; pharynx; pig NONHUMAN MAMMALS transport food or liquid through the mouth in consecutive cycles so that it accumulates in the valleculae, a space between the back of the tongue and the front of the epiglottis (20, 52, 54). However, emptying of this space, a pharyngeal swallow, occurs only intermittently. In the decerebrate animal, emptying of the vallecular space occurs "reflexly," with fluid delivery to the area (39, 52) or with electrical stimulation of the sensory fibers of the superior laryngeal nerve (24). In this situation, the term reflexly means the activation of a brain stem pattern generator (4, 15) and not a classical oligosynaptic reflex arc. Fifty years ago, in a classic paper, Doty and Bosma (10) described the pattern of activation of oropharyngeal muscles involved in this response, although using a variety of eliciting stimuli. Their work led to the general acceptance that the pharyngeal stage of swallowing consists of a centrally generated, temporally ordered sequence of bursts of electromyographic (EMG) activity in the oropharyngeal muscles. Their summary figure, showing the order of activation of oropharyngeal muscles in the reflex pharyngeal swallow, rapidly became and has remained the standard diagram for many textbooks of physiology or dysphagia. There has been no reinvestigation of the EMG activity of behaviorally isolated pharyngeal reflex swallowing since Doty and Bosma (10). Neither has there been an attempt to isolate the EMG components that are specific to the pharyngeal swallow, although there have been several studies of EMG activity during ingestion and swallowing in intact animals (26, 28, 31, 52, 57) . The work of Doty and Bosma (10) led to a consensus that the mylohyoid muscle was the lead muscle in the sequential pattern of muscle activation. However, they (10) very carefully describe their classic figure as only a "schematic summary" in which the "contours of the rise and fall of activity are not considered accurate." They also repeatedly emphasize the variability of the signals they recorded, stating that "there was wide variation in the duration of activity in various muscles" and that "not two EMGs of deglutition from the same electrodes gave identical or even similar unit patterns." Such comments suggested that reinvestigation was justified. Our initial hypothesis was that the reported variation was largely due to the technology available at that time. The study by Doty and Bosma (10) predated both the description of the size principle in the recruitment order of motor units and the finding of exceptions to that order (7). It also predated the discovery of different task units within individual muscles (13, 58) and the discovery that different initiating stimuli could alter the subsequent pattern of activity in swallowing (41). These studies raise the possibility that the variability reported by Doty and Bosma (10) also included what were then unrecognized factors. We tested two hypotheses: 1) that the variation in EMG activity reported by Doty and Bosma (10) could be reduced if the pharyngeal swallows were elicited using a single natural stimulus and more recent EMG recording techniques; and 2) that the reported variation in EMG activity could be explained by the selective recording characteristics of the electrodes detecting different types of motor units. Although not used in the Doty and Bosma (10) study, we used the decerebrate infant pig model for two reasons. First, considerable information is available on the feeding mechanisms of the intact piglet (16 -