Cortical activation during solid bolus swallowing.

Specific areas of cortical activity during solid bolus swallowing in humans are unknown. We tested the hypothesis that cortical representations of swallowing in humans may vary by bolus type. Twenty-one normal subjects swallowed three kinds of food: agar (solid), a capsule and water. We followed the same countdown method for identification of the cortical representations during swallowing performances as a previous study (Tanaka et al., 2006). Functional magnetic resonance imaging (fMRI) showed that the precentral gyrus, postcentral gyrus, medial temporal gyrus, superior temporal gyrus and cingulate gyrus were activated when swallowing an agar bolus (p<0.001). The subcortex was not activated. The cerebellum was activated only during capsule swallowing (P<0.001). Water bolus swallowing activations were similar to agar bolus swallowing. The cluster size of water swallowing was larger than the agar swallowing. We conclude that the cortical representations for swallowing are variable by food type.