Evaluating muscles underlying tongue base retraction in deglutition using muscular functional magnetic resonance imaging (mfMRI)

Purpose: Tongue base retraction during swallowing is critical to bolus propulsion in normal physiological swallowing. A better understanding of the hyoglossus and styloglossus, muscles thought to be key to tongue base retraction, will improve the quality of physical rehabilitation in dysphagic patients in addition to preventing iatrogenic damage to structures critical to deglutition. This study utilized muscle functional MRI in healthy adult human subjects in order to determine if the hyoglossus and styloglossus are active during swallowing. Methods and materials: Data were collected for 11 subjects with mfMRI before and after swallowing, and after performing the Mendelsohn maneuver. Whole muscle relaxation time profiles (T2 signal in milliseconds) were calculated from weighted averages of multiple dual echo MRI slices, allowing for comparison of physiological response for the muscles in each test condition. Changes in effect size (Cohen's d) of whole muscle T2 profiles were used to establish whether or not the hyoglossus and styloglossus are utilized during swallowing and during the Mendelsohn maneuver. Results: Post-swallowing effect size changes (where a d value of > 0.20 indicates significant activity) for the T2 signal profiles of the hyoglossus and styloglossus were found to be d = 1.19 and 0.22, respectively. The hyoglossus showed an effect size change of d = 0.26 for the Mendelsohn maneuver. Conclusions: Muscle functional MRI indicates a physiological response of the hyoglossus and styloglossus during swallowing, and the hyoglossus during the Mendelsohn maneuver.