German, R Z

Thexton, A J

Suckling and drinking are rhythmic activities, with an electromyographic pattern that is characterized by a significant coactivation of multiple muscles that are not obvious synergists. If the rhythm and coactivation were due to conventional excitation of motor neurons by a single, central source of rhythm generation then, within the periods of coactivation, there should also be a degree of synchronization of muscle action potentials, similar to that established for respiration. Both respiration and suckling are activities that can persist in the absence of the cerebral hemispheres. However, in a preliminary study of suckling, evidence for synchronization was not characteristic of most of the coactive muscles. Marked rhythmic coactivation of muscles is also characteristic of the cerebrally directed, more mature activity of drinking. Synchronization of action potentials in other conscious movements suggests that cerebrally directed drinking might differ from suckling with respect to the level of synchronization. We tested this hypothesis in miniature pigs by cross-correlation analysis of the electromyographic activity recorded in multiple oral and submandibular muscles during suckling and drinking in the same animals. Evidence of intraburst synchronization was found in only a few muscles (sternohyoid, omohyoid, and geniohyoid) during suckling, but that evidence was absent in drinking suckling, but that evidence was absent in drinking in exactly the same muscles in the same animals. A tentative explanation for the paucity of evidence for synchronization in suckling, despite the coactivation of muscles, is that the rhythmic muscle activity is generated by plateau potentials in individual motor neurons; this is a phylogenetically primitive mechanism with respect to mammals. The absence of evidence for synchronization in drinking may reflect the fact that the neural mechanisms for drinking precede those for suckling phylogenetically, although not ontogeneticall

Synchronization of electromyographic activity in oral musculature during suckling and drinking

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