BEHAVIORAL-CONTROL OF BREATHING IN THE CAT

Respiration depends upon brainstem neuronal circuits that produce the respiratory rhythm and relay it, via the ventrolateral columns, to motor neurons in the spinal cord. This brainstem system produces respiration automatically, i.e. without conscious effort, and is responsive to chemical and mechanical stimuli that signal imbalances in respiratory homeostasis. In addition to this automatic/metabolic respiratory system, there is a voluntary/behavioral system that controls the respiratory muscles during speaking, breath holding, and other voluntary respiratory acts. It has been proposed that this behavioral system involves corticofugal fibers that bypass the automatic system, course in the dorsolateral columns, and end at the level of the respiratory motor neurons. According to this scheme, the integration of behavioral control with automatic/metabolic control occurs at the level of the motor neurons and not within the automatic system. This proposed scheme has not been investigated experimentally. In the present study, we trained cats to control their respiration and recorded the activity of cells within the automatic system in the medulla during this behavioral control. We trained the animals to terminate inspiration and prolong expiration when a tone sounded. Microelectrode recordings from 40 medullary respiratory neurons showed that most cells, inspiratory and expiratory, became inactive during the behavioral apneic response. The exceptions were some expiratory cells that were activated during the task. These results suggest that the integration of behavioral influences occurs within the automatic system.