Cortical compensation associated with dysphagia caused by selective degeneration of bulbar motor neurons

According to recent neuroimaging studies, swallowing is processed within multiple regions of the human brain. In contrast to this, little is known about the cortical contribution and compensatory mechanisms produced by impaired swallowing. In the present study, we therefore investigated the cortical topography of volitional swallowing in patients with X-linked bulbospinal neuronopathy (Kennedy disease, KD). Eight dysphagic patients with genetically proven KD and an age-matched healthy control group were studied by means of whole-head magnetoencephalography using a previously established swallowing paradigm. Analysis of data was carried out with synthetic aperture magnetometry (SAM). The group analysis of individual SAM results was performed using a permutation test. KD patients showed significantly larger swallow-related activation of the bilateral primary sensorimotor cortex than healthy controls. In contrast to the control group, in KD patients the maximum activity was located in the right sensorimotor cortex. Furthermore, while in nondysphagic subjects a previously described time-dependent shift from the left to the right hemisphere was found during the one second of most pronounced swallow-related muscle activity, KD patients showed a strong right hemispheric activation in each time segment analyzed. Since the right hemisphere has an established role in the coordination of the pharyngeal phase of swallowing, the stronger right hemispheric activation observed in KD patients indicates cortical compensation of pharyngeal phase dysphagia.