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Hemispheric Dominance of Tongue Control Depends on the Chewing-side Preference

¹ Maxillofacial Orthognathics,
² Oral/Maxillofacial Radiology, and
³ Cognitive Neurobiology, Graduate School, Tokyo Medical and Dental University, 5-45, Yushima 1-chome, Bunkyo-Ku, Tokyo 113-8549, Japan;
⁴ Department of Physiology, Nihon University, School of Medicine, Tokyo 113-8610, Japan; and
⁵ Department of Oral and Maxillofacial Radiology, the University of Tokushima, Tokushima 770-8503, Japan;

View larger version (17K): [in a new window]   Figure 1. Representative simultaneous recordings of electromyographic activities of orofacial muscles and tongue pressure during visual feedback training of tongue movements. Electromyographic activities were recorded from bilateral anterior and posterior temporalis, masseter, and digastric muscles, and tongue pressure was recorded bilaterally by a pressure transducer. The subject performed tongue movement (i.e., lateral excursion of the tongue tip to touch the ipsilateral pressure transducer) between the two arrows. Note that while bilateral activation of several orofacial muscles was seen with tongue moments during clenching and swallowing, lateral tongue movements could be performed (between arrows) with a minimum activation of orofacial muscles and without touching the contralateral pressure transducer. The horizontal bar denotes 1.0 sec. Vertical bars denote 50 mV for TR and TL, 200 mV for clenching and swallowing in EMG records, and 20 g/cm2 for tongue pressure. Abbreviations: TR, tongue movement to the right; TL, tongue movement to the left.

View larger version (78K): [in a new window]   Figure 2. Task design and brain activities. (A) Experimental design of the tongue-movement paradigm indicating the alternation of "rest" and tongue-movement tasks. See text for details. (B) Projections of the activation foci on the lateral surface of a standard human brain atlas during tongue movements (i.e., TP, TR, and TL) revealed by a random-effect analysis. a, TP-"rest"; b, TR-"rest"; c, TL-"rest". Significant activations (p < 0.001 uncorrected for multiple comparisons) of bilateral S1/M1 cortices are shown. Note that there were no marked differences in activation foci for the 3 different tongue movements in terms of size or location. (C) Representative activation patterns in the S1/M1 of subjects with evident chewing-side preferences on the given sectional planes (z = 30). a, subject with a chewing-side preference exclusively on the left. b, subject with a chewing-side preference exclusively on the right. Activations of bilateral S1/M1 cortices that were significant (p < 0.05 corrected) are shown. Color code denotes T-values. Abbreviations: Tp, tongue protrusion; TR, tongue movement to the right; TL, tongue movement to the left; R, right side.

View larger version (25K): [in a new window]   Figure 3, Comparisons of BOLD signals. (A) a, Comparisons of the mean BOLD signal change between the right and left S1/M1 during TP, TR, and TL (a) as well as TP+R+L (b) in all 15 subjects. (B) Comparisons of the mean BOLD signal change in the S1/M1 between the hemispheres contralateral and ipsilateral to the preferred chewing side during TP+R+L in the five subjects with an evident left chewing-side preference. (C) Comparisons of the mean BOLD signal change in the S1/M1 between the hemispheres contralateral and ipsilateral to the preferred chewing side during TP+R+L in the five subjects with an evident right chewing-side preference. (D) Comparisons of the mean BOLD signal change in the S1/M1 between the hemispheres contralateral and ipsilateral to the preferred chewing side during TP+R+L in the subjects with an evident chewing-side preference. Solid bars indicate standard deviations. Abbreviations: CSP, chewing-side preference; right, right hemisphere; left, left hemisphere: contra, the hemisphere contralateral to the preferred chewing side; ipsi, the hemisphere ipsilateral to the preferred chewing side. *p < 0.05, ***p < 0.001.