The functional neuroanatomy of voluntary swallowing

Swallowing is a complex physiological process involving voluntary and reflexive motor activity, sensorimotor integration, salivation, and visceral regulation. Despite the numerous processes required for normal deglutition, traditional models of the central control of swallowing only emphasize the involvement of the brainstem and the inferior precentral gyrus (IPCG). However a number of neurological disorders involving other brain regions also cause dysphagia. To determine the brain regions participating in voluntary swallowing, we assayed regional cerebral blood flow (rCBF) with positron emission tomography (PET) while healthy human subjects swallowed, performed lateral tongue movements, or rested with their eyes closed. Voluntary swallowing produced strong rCBF increases within the IPCG bilaterally, the right anterior insula/claustrum, and the left cerebellum. The maxima in these regions differed from those induced by lateral tongue movements. Swallowing also produced rCBF increases in the putamen, thalamus, and several additional cortical areas, but these foci were not as clearly distinguishable from activity arising during tongue movements. These findings indicate that swallowing involves the recruitment of a large-scale distributed neural network that includes the anterior insula and cerebellum. The distributed nature of this network helps to explain why so many neurological conditions produce dysphagia.