Activity In Single Hypoglossal Fibers During Cortically Induced Swallowing And Chewing In Rabbits

SummaryIn rabbits under light ether anesthesia, rhythmic movements of chewing and swallowing were produced by stimulation to the antero-lateral cortex. The activity of hypoglossal motor fibers during such stimulation was studied, together with changes evoked by stimulation of the superior laryngeal nerve.1.Most hypoglossal motor fibers discharged bursts of impulses in phase with the cortically evoked rhythmic chewing, the majority being concurrent with jawclosing. Among these, some units fired with fairly constant latency after each stimulus, while others had no consistent relation to the stimuli in the train. A few units bore no relation to the rhythm of chewing in their discharge of impulses, either following regularly to each stimulus or occurring sporadically.2.In the hypoglossal units discharging grouped impulses in phase with chewing, some displayed also a characteristic burst, whereas others ceased discharging momentarily when a swallow occurred during cortical stimulation.3.The shortest time for cortico-hypoglossal conduction ranged from 5.8 to 12.0 msec, indicating polysynaptic linkage for the path.4.Cortically evoked rhythmic chewing was arrested by stimulation of the superior laryngeal nerve. During this period, one group of hypoglossal units ceased discharging completely, while others discharged impulses regularly after each stimulus pulse.5.Motoparalysis did not alter the pattern of discharge of the hypoglossal nerve fibers by cortical and/or superior laryngeal stimulation, though abolishing totally the movement of chewing and swallowing.6.The relevance of these findings to the central neural arrangement for the control of rhythmic chewing and swallowing is discussed.