Time-dependent hemispheric shift of the cortical control of volitional swallowing.

An important part of the cortical processing of swallowing takes place in the sensorimotor cortex, predominantly in the left hemisphere. However, until now, only deglutition related brain activation with low time resolution exceeding a time interval of 1 s has been reported. In this study, we have examined the chronological sequence of cortical swallowing processing in humans by means of high temporal resolution magnetoencephalography (MEG). The cortical MEG activity was recorded during self-paced volitional swallowing in 10 healthy subjects. Data were analyzed using synthetic aperture magnetometry and the group analysis was performed using a permutation test. Swallowing-related muscle activity was recorded by electromyography. Within the time interval of 1 s of the most pronounced muscular swallowing execution, the MEG analysis revealed neural activation in the primary sensorimotor cortex. During the first 600 ms, only left hemispheric activation was found, bihemispheric activation during the next 200 ms and a right hemispheric activation during the last 200 ms. Thus, our results demonstrate a time-dependent shift of neural activation from left to right sensorimotor cortex during deglutition with left hemispheric dominance in the early stage of volitional swallowing and right hemispheric dominance during its later part.