There are wide intra- and inter-individual variations in human chewing trajectories. This study aimed to develop the way of describing the intra-individual variations in chewing trajectories and investigate their inter-individual resemblances. The chewing trajectories of 12 healthy males who chewed gum in the right side of their mouth were recorded. Overall cycle shape was described with 123 variables consisted of three-dimensional coordinates of total 41 points at which the durations of the opening and closing phase of a chewing cycle was divided into 20 parts equally. The intra-individual variations in 200 chewing trajectories were evaluated with the principal component (PC) analysis based on a variance-covariance matrix of the variables. The variation in the trajectories that was accounted for by each PC was visualized as a reconstructed curve by using an inverse eigenvector matrix. In all subjects, the first PC was related to the changes in the gape width in each subject. Among the other PCs, which were selected by means of the scree plot analysis, two were related to the changes in the jaw-opening direction in the frontal or sagittal planes, and other one was related the width between the opening and closing trajectories. The above 4 PCs explained 74% to 87% of the variances in each of the subjects. Moreover, among the 7 PCs, which account more than 95% of the variations of the total of 2,400 chewing trajectories of all the subjects, 4 showed the similar effects on the trajectory changes as mentioned above. Inter-individual resemblances were present among the intra-individual changes in the chewing trajectories. This would suggest that the subjects utilized identical strategies in controlling chewing trajectories.

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The present study was undertaken to validate how descent of the hyoid position, considered as a pathological condition of dysphagia, affect swallowing function by evaluating spatial and temporal hyoid excursion, hyoid position and bolus transmission in healthy volunteers and patients with dysphagia.
 All subjects, including 65 patients with dysphagia and 10 normal volunteers, were examined using videofluorographic images. These images were analyzed to measure the time series of hyoid movement and bolus transmission based on the moment the tip of the tongue starts to move. The hyoid position was also investigated, and the origin was defined on the anterior ridge of the fourth cervical vertebra. Statistical comparison between both groups was then performed.
 The oral and pharyngeal transit times were prolonged in the patient group; in addition, entry of the bolus head into the pharynx was significantly earlier than the start of pharyngeal swallowing (start of the rapid hyoid elevation). There was no significant difference in the hyoid position between the two groups when the origin was defined on the anterior ridge of the fourth cervical vertebra. Further evaluation was performed by classifying patients with dysphagia by the diseases causing their dysphagia. A similar hyoid trajectory among the classified groups was observed after the onset of the swallowing reflex; in contrast, the hyoid bone showed complicated movement before the swallowing reflex occurred. The hyoid position may affect the delay in the swallowing onset because positive correlation between the distance and time of hyoid movement was observed before swallowing reflex in some diseases.

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[Purpose] To clarify the relationship between head position and blood flow in masseter muscles, masseter hemodynamic change caused by head inclination was investigated.
 [Methods] Sixteen healthy subjects participated in this study. Blood flow in masseter muscles was measured by using a three-wavelength near-infrared spectroscope, and the angle of head inclination was measured by using a head inclination measuring device. The subjects were instructed to incline their head forward or laterally at angles of 10, 20 and 30 degrees, and total hemoglobin volume (Hb) and oxygen saturation level (StO₂) during head inclination were measured. In addition, blood flow in masseter muscle before and after maximum voluntary contraction was measured and compared with that during head inclination.
 [Results] The percentage of changes in Hb during forward and lateral inclinations of the head were significantly larger than those during rest. Moreover, Hb change during head inclination of 30 degrees was about half of the maximum change after maximum voluntary contraction. On the other hand, the percentage of change StO₂ change during head forward inclination of 30 degrees was significantly larger than that during rest and was about 40% of the maximum change after maximum voluntary contraction. The percentage of change in StO₂ change during head lateral inclination was not significantly larger than that during rest.
 [Conclusions] The results suggest that blood flow in masseter muscles is changed by head inclination. Therefore, head posture must be kept constant during blood flow measurements of masseter muscles.

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Our brain analyzes a visual world in two visual information processing systems. In those systems, visual information is broken down into shape, color, depth and motion information, and analyzed. However, our brain does not simply analyze information in detail, but interprets under several constrained conditions. In such situation, many optical illusions are experienced.

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Patients with dysphagia often aspirate food and thickeners or gelling agents are, therefore, used in foods for dysphagic patients. To determine the appropriate properties as foods for dysphagic patients, however, it is important to know quantitatively the flow aspects of the bolus in the pharynx. The ultrasonic pulse-Doppler method is safer for the human body than the well-known Videofluorography (VF) and is useful to obtain the velocity distribution of the bolus through the pharynx. The maximum velocity, V_max of water, which is often aspirated into trachea of patients with dysphagia, was about 3 times higher than that of yogurt, which is rarely aspirated. Thus, the risk of aspiration for patients with dysphagia can be predicted from the value of V_max.

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