Investigation of changes in the interaction of cerebral cortex during the oral swallowing task.

Background: The main swallowing activities in the oral phase include chewing and tongue movements. Cortical control is essential for the initiation and coordination of swallowing activities in the oral phase.

Research Purposes: This study aims to further investigate whether there are differences neural mechanisms in cortical interactions underlying oral phase by simulating chewing and tongue movement.

Methods: This study recruited 25 healthy adult participants, by functional magnetic resonance imaging to collect data in the Empty chewing task and Tongue-to-Palate posterior Retraction task. The Dynamic causal modelling and Parametric Empirical Bayes were used to analyze the best model and the effective connectivity between brain regions under different tasks.

Results: In the Empty Chewing task, the primary motor cortex(M1) is the main driving input brain area with significant excitatory connectivity with the primary somatosensory cortex(S1) and supplementary motor area(SMA). However, in the Tongue-to-Palate posterior Retraction task, S1 becomes the main driving input brain area and maintains bidirectional connections with M1 and SMA, but S1 shows an inhibitory effect on SMA.

Conclusion: This study reveals the differences in the interaction among brain regions during the oral swallowing activity. Results suggest M1 and SMA interaction is vital for the whole oral phase. M1 is a key brain region for Empty chewing task, while S1 is important for sensory feedback. S1 may inhibit SMA during the Tongue-to-Palate posterior Retraction task to aid swallowing and reduce interference with the pharyngeal swallowing action.