Switching on swallowing, switching on the brain - a new approach for the treatment of dysphagia

Background/aims: Animal studies demonstrate that stimulation of both the cerebral cortex and brainstem can provoke swallowing. Peripheral, sensory input is also important for normal swallowing, since altered sensation can affect swallowing performance. Our aim was to identify, in healthy adults, the physiologic changes in cortical and brainstem activity that occur during normal swallowing, and then examine the effect of altered sensation (either sensory stimulation or topical anaesthesia of the swallowing musculature) on this activity. We then show that sensory stimulation can be applied to stroke patients with dysphagia (difficulty swallowing) and produce a quantifiable improvement in swallowing performance. Methods: Techniques involved water swallowing; electrical, sensory stimulation of swallowing musculature by intraluminal catheter with ring electrodes; topical anaesthesia by lidocaine spray; transcranial magnetic stimulation (TMS), functional magnetic resonance imaging (fMRI) and videofluoroscopy (VFS). Results: Normal subjects (as recorded with TMS): (i) An increase in both cortical and brainstem activity occurred during water swallowing. (ii) Sensory stimulation, depending on the stimulus parameters, provoked either long-lasting suppression, or enhancement of activity within cortex but not brainstem. (iii) Topical anaesthesia suppressed cortical activity. Normal subjects (as recorded with fMRI): (iv) Sensory stimulation at the optimal parameters leading to enhancement of cortical activity, prior to swallowing, resulted in stronger, bilateral, hemispheric activation compared to swallowing alone. Dysphagic stroke patients: (v) Sensory stimulation both enhanced cortical activity within the undamaged (but not damaged) hemisphere and at the same time produced a clear improvement in swallowing performance compared to sham. Conclusions: Normal swallowing leads to activation within brainstem and cortex. Altered sensation may suppress or enhance this activity. "Beneficial" sensory stimulation at the optimal parameters, leads to greater activation of areas of brain functionally important for swallowing. When this is applied to dysphagic stroke patients, cortical activity is also enhanced, predominantly in the undamaged hemisphere, and a clear improvement in swallowing performance is produced. Sensory stimulation therefore provides us with a new and exciting, physiologic technique for managing dysphagia, particularly after stroke.