Integration of the Reflex Pharyngeal Swallow Into Rhythmic Oral Activity in a Neurologically Intact Pig Model

Mammalian swallowing involves the coordinated and sequential activity of many oropharyngeal muscles. Using synchronous electromyography (EMG) and videofluorography, we recorded the pattern of EMG activity for 12 muscles during swallowing in neurologically intact suckling pigs. We tested the hypothesis that this EMG pattern corresponded to the established pattern of activity for the isolated, reflexive pharyngeal swallow of the decerebrate infant pig. The EMG activity associated with the normal swallow of the intact animal had two components: a staggered pattern of single EMG bursts that were prominent in the stylohyoid, thyrohyoid, cricothyroid, and omohyoid muscles and double bursts of activity in some muscles, including geniohyoid and genioglossus, with the same underlying periodicity as suckling. Most of the staggered activity pattern, a linear sequence of progressively delayed activities in different muscles, was not statistically different from that previously found in the reflexive pharyngeal swallow of the decerebrate. However, not all components of the linear sequence of the reflexive swallow were inserted unchanged into the intact swallow. Some components appeared to be delayed or advanced, bringing them into phase with the underlying rhythmic activity. The difference between swallows of intact and of decerebrate animals was not solely due to the presence of rhythmic activity in the former. The timing of some EMG activities in intact animals also differed from the same activities in the few decerebrates that exhibited rhythmic tongue and jaw activity. These results suggest cerebral function influences the EMG pattern of the pharyngeal swallow, which has traditionally been considered a purely reflex pattern

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

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

Ontogenetic Changes in Mammalian Feeding: Insights from Electromyographic Data

All infant mammals make a transition from suckling milk to eating solid foods. Yet, the neuromuscular implications of the transition from a liquid-only diet to solid foods are unknown even though the transport and swallowing of liquids is different from that of solids. We used legacy electromyography (EMG) data to test hypotheses concerning the changes in motor pattern and neuromuscular control that occur during the transition from an all-liquid diet to consumption of solid food in a porcine model. EMG signals were recorded from five oropharyngeal muscles in pigs at three developmental stages (infants, juveniles, and adults) feeding on milk, on food of an intermediate consistency (porridge), and on dry chow (juveniles and adults only). We measured cycle frequency and its variation in “transport cycles” and “swallow cycles”. In the swallow cycles, a measure of variation of the EMG signal was also calculated. Variation in cycle frequency for transport and swallow cycles was lowest in adults, as predicted, suggesting that maturation of feeding mechanisms occurs as animals reach adulthood. Infants had lower variation in transport cycle frequency than did juveniles drinking milk, which may be due to the greater efficiency of the infant’s tight oral seal against the teat during suckling, compared to a juvenile drinking from a bowl where a tight seal is not possible. Within juveniles, variation in both transport and swallow cycle frequencies was directly related to food consistency, with the highest variation occurring when drinking milk and the lowest when feeding on solid food. There was no difference in the variation of the EMG activity between intact infants and juveniles swallowing milk, although when the latter swallow porridge the EMG signals were less variable than for milk. These results suggest that consistency of food is a highly significant determinant of the variation in motor pattern, particularly in newly weaned animals