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 reduced 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.

No abstract

The cycles of jaw and tongue movement during feeding produce not only the breakage of food but its intra-oral transport; which activity predominates depends upon the physical characteristics of the food. When hard food is eaten and tooth-food-tooth contact is made during jaw closure, the velocity of closing is suddenly reduced, producing two clearly different phases of closure; during the second phase the activity of the jaw closing muscles is much increased. Conversely, in cycles with a mainly transport function (eating soft food), the antero-posterior movements of the tongue are much greater; this alters the time and rate at which the jaw opens. The pattern of jaw movement during closing and during opening consequently varies with food consistency. The evidence suggests that sensory input controls the form of the cyclical tongue and jaw movements. However the basic plan of movement is produced by the activity of a brainstem pattern generator which receives input from both cerebro-cortical and peripheral sources. The swallow that occurs in normal feeding consists of the equivalent of the classical second stage of swallowing inserted into the occlusal or initial jaw opening phase of an otherwise standard cycle. Although leakage of traces of food or saliva into the vallecula appears to be a peripheral sensory input of major importance in inducing such a swallow, the execution of the swallow is due to a pattern generator in the brainstem.

No abstract