## 4 Discussion  
The present investigation suggests that both tongue elevation and protrusion during swallowing activate a widely distributed network of cortical and subcortical areas, but with different configurations. The most consistent finding was recruitment of the bilateral primary motor and premotor cortex, bilateral supplementary motor area (SMA) [55] and the cerebellar activation during these tasks. A possible explanation could be that swallowing tasks involve cooperation of the motor components in planning tongue protrusion and elevation and refining oropharyngeal movements based upon sensory input by the cerebellum. The activation of these areas during oropharyngeal movements such as speech production [56], perception [57], and swallowing have been reported by a consistent number of studies [24; 31; 33]. According to these studies [18; 24; 33], the primary motor cortex and the cerebellum are activated only during repetitive saliva swallowing tasks, consistent with our investigation on tongue protrusion and elevation, and there is at least one study that shows that the repetitive saliva swallowing increases demands on the \"swallowing\" neuronal network [33; 34]. In contrast, other studies that did not consider repetitive saliva swallowing [19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58], did not observe the foci activation. There is emerging evidence showing how the premotor areas are not solely involved in motor programming and movement initiation but also in sensory processing [59] and may be regarded as supplementary sensorimotor areas [60]. In our investigation, despite similar activations between tasks of tongue protrusion and elevation in swallowing, the cluster size of brain activation for the protrusion task was larger than the elevation task and differently distributed. This may have occurred because protrusion involved greater motor effort than elevation, suggesting that swallowing with the tongue in protrusion requires the involvement of many regions in the cerebral cortex and subcortex. Moreover, due to the specific physiology of the genioglossus muscle, [61]. which is the main muscle involved in maintaining the airways patent, a tongue trusting is a well-documented physiological response to airways disturbances, and it involves compensatory sensory motor recruitment reflected in the increased cortical and subcortical activation. Consistent with the principles of neuroplasticity employed during swallowing therapy or in myofunctional therapy, practicing a task changes the activation patterns within the cortical network involved in each task or produces functional reorganization, which indicates that the brain regions recruited for each task are altered as a function of practice [62; 63]. It is also well recognized that a highly practiced task requires less brain activation when compared to a less practiced one or a task's initial learning phase [64]. Further practice may eventually lead to new changes in the cortical motor outputs. This means there is a pattern of decreased global activation as well as a shift in activity from cortical to subcortical areas as automaticity is achieved [65; 66], important for generalization and habituation of