Modulation of esophageal responses to magnetic stimulation of the human brain by swallowing and by vagal stimulation.

Abstract

Although magnetic stimulation of the human cerebral cortex activates corticoesophageal pathways, it is not known whether these pathways are mediated via brain stem neurons activated during swallowing and by vagal afferents. The aim of this study was to determine the effect of swallowing and vagal stimulation on esophageal electromyographic responses evoked by magnetic stimulation of the human cortex. Magnetic stimulation of the cortex was performed in 7 subjects at variable intervals after swallows and at intervals ranging from 10 to 200 milliseconds after vagal stimulation in 5 subjects. Between swallows, cortical stimulation induced both early (10.1 +/- 0.5 milliseconds) and late (52.3 +/- 2.3 milliseconds) esophageal electromyographic responses with amplitudes of 66.9 +/- 23.4 microV and 32.9 +/- 7.4 microV, respectively. During swallowing, both responses were facilitated because their latencies decreased (8.9 +/- 0.5 milliseconds and 47.3 +/- 4.8 milliseconds, respectively), whereas their amplitudes increased (203.1 +/- 54 microV and 79.8 +/- 22.5 microV, respectively). Vagal stimulation facilitated the early cortically evoked response. Its latency decreased from 10.2 +/- 0.2 milliseconds to 8 +/- 0.2 milliseconds, whereas its amplitude increased from 145.1 +/- 44 microV to 230.5 +/- 41.6 microV. Corticoesophageal pathways activated by magnetic stimulation of the human cortex share the same population of brain stem motor neurons to the upper esophagus that are activated during swallowing and vagal stimulation.