The neurobiology of swallowing and dysphagia.

The neurobiological study of swallowing and its dysfunction, defined as dysphagia, has evolved over two centuries beginning with electrical stimulation applied directly to the central nervous system, and then followed by systematic investigations that have used lesioning, transmagnetic stimulation, magnetoencephalography, and functional magnetic resonance imaging. The field has evolved from mapping the central neural pathway and peripheral nerves, to defining the importance of specific regions of the lower brain stem in terms of interneurons that provide sequential control for multiple muscles in the most complex reflex elicited by the nervous system, the pharyngeal phase of swallowing. The field is now emerging into defining how the higher cortical regions interact with this brain stem control and is providing a broader perspective of how the intact nervous system functions to control the three phases of swallowing (i.e., oral, pharyngeal, and esophageal). Much of the present interest focuses on how to retrain a damaged nervous system using a variety of stimulus techniques, which follow fundamentals in rehabilitation of the nervous system.