Tongue Posture, Tongue Movements, Swallowing, and Cerebral Areas Activation: A Functional Magnetic Resonance Imaging Study

The aim of this study was to pinpoint the cerebral regions implicated during swallowing by comparing the brain activation areas associated with two different volitional movements: tongue protrusion and tongue elevation. Twenty-four healthy subjects (11-males 22 +/- 2.9 y; 13-females 23 +/- 4.1 y; were examined through functional magnetic resonance imaging (fMRI) while performing two different swallowing tasks: with tongue protrusion and with tongue elevation. The study was carried out with the help of fMRI imaging which assesses brain signals caused by changes in neuronal activity in response to sensory, motor or cognitive tasks. The precentral gyrus and the cerebellum were activated during both swallowing tasks while the postcentral gyrus, thalamus, and superior parietal lobule could be identified as large activation foci only during the protrusion task. During protrusion tasks, increased activations were also seen in the left-middle and medial frontal gyrus, right thalamus, inferior parietal lobule, and the superior temporal gyrus (15,592-voxels; Z-score 5.49 +/- 0.90). Tongue elevation activated a large volume of cortex portions within the left sub-gyral cortex and minor activations in both right and left inferior parietal lobules, right postcentral gyrus, lentiform nucleus, subcortical structures, the anterior cingulate, and left insular cortex (3601-voxels; Z-score 5.23 +/- 0.52). However, the overall activation during swallowing tasks with tongue elevation, was significantly less than swallowing tasks with tongue protrusion. These results suggest that tongue protrusion (on inferior incisors) during swallowing activates a widely distributed network of cortical and subcortical areas than tongue elevation (on incisor papilla), suggesting a less economic and physiologically more complex movement. These neuromuscular patterns of the tongue confirm the different purpose of elevation and protrusion during swallowing and might help professionals manage malocclusions and orofacial myofunctional disorders.