Regional intercostal activity during coughing and vomiting in decerebrate cats.

Regional variations in the discharge patterns of the internal and external intercostal muscles of the middle and caudad thorax were studied in decerebrate, spontaneously breathing cats during coughing and vomiting. Coughing, induced by electrical stimulation of the superior laryngeal nerves, consisted of increased and prolonged diaphragmatic activity followed by a burst of abdominal activity. Mid-thoracic external and internal intercostal muscles discharged synchronously with the diaphragm and abdominal muscles, respectively. Caudal external and internal intercostal muscles, however, discharged synchronously with the abdominal muscles. Vomiting, induced by stimulation of the lower thoracic vagi, consisted of a series of synchronous bursts of diaphragmatic and abdominal activity (retching) followed by a prolonged abdominal discharge after the cessation of diaphragmatic activity (expulsion). Caudal external and internal intercostals discharged in phase with diaphragmatic and abdominal activity but both mid-thoracic intercostal muscles discharged out of phase with these muscles. These results indicate major differences in the control and functional roles of intercostal muscles at different thoracic levels during these behaviours.