The shape of human tongue plays an important role in oral cavity functions such as speaking, chewing, swallowing, and breathing. In this study, the authors constructed a mathematical model of the tongue using the mass-spring model and simulated tongue deformation during vowel production. The viscoelasticity of tongue tissues are represented by the Kelvin-Voigt model. Contraction of lingual muscles are represented by a muscle model composed of a constractile component, springs, a damper, and mass. Incompressibility of muscles is an important factor that affects tongue shape. In this study, the potential energy function generated by compression of tissues is defined. Muscle incompressibility is modeled by minimizing the energy function in the deformation process. The authors simulated tongue deformation during Japanese vowel production. Tongue muscles are classified into eight groups, and the muscle length is defined based on an MR image. The results are in good agreement with the MR imaging results of deformation of the tongue in the sagittal plane. Further, this simulation can qualitatively represent tongue deformation in producing Japanese vowel “a”.
The objective of this study was to investigate the effect of aroma inhalation on salivary cortisol secretion during sleep and after awakening. We used two essential oils that are known to have opposite effects on the behavior of the autonomous nervous system:lavender that induces the parasympathetic nervous system, and jasmine that induces the sympathetic nervous system. These substances were administered to subjects using an olfactometer, by which the volatilized odorants were intermittently delivered through a cannula (first 1 min of each 5-min interval) during the six-hour sleep period. Eighteen male students (aged 20-24 years) participated in the study and received each odorant (lavender, jasmine or scentless air [control]) each night in a counterbalanced order. Saliva samples were collected every 30 min while the subjects were asleep and every 15 min for 1 h after awakening, using proprietary saliva collection equipment. Salivary cortisol level during 15 min after awakening was significantly higher after lavender aroma inhalation compared to jasmine aroma (p < 0.01) or control (p < 0.05) inhalation. After lavender aroma inhalation, recovery from subjective fatigue indicated by Profile of Mood States (POMS) score was significantly higher compared to jasmine aroma (p < 0.05) and tended to be higher compared to control (p < 0.10). Increased secretion of salivary cortisol is associated with activation of the hypothalamus-pituitary-adrenal (HPA) system. Our results suggest that inhalation of lavender aroma during sleep augments the HPA activity, and may enhance recovery from subjective fatigue upon awakening.
Extracellularly recorded neuronal activity contains spikes superimposed on local field potentials (LFPs). With a proper filter, spiking activity can be separated from the LFP. Correlated activities of the spikes and synchronizations of the LFPs recorded by multichannel electrodes have been reported in cat early visual cortex, but the neural mechanisms underlying these correlations and the synchronizations are not well understood. In the present study, multichannel recording electrodes were placed in the cat early visual cortex, and both neuronal spikes and LFPs were recorded in order to investigate their correlative activity and synchronization. Areas 17 and 18, which comprise the cat early visual cortex, were identified by using optical imaging based on intrinsic signals, according to the difference of their preferred spatial frequencies before the electrophysiological recording. The optimal spatial frequency stimuli for areas 17 and 18 were presented during the electrophysiological experiment. The correlation and synchronization of neuronal activities in different sites were evaluated by using cross-correlograms (CCGs) for the spiking activity between the cells, and phase-locking values (PLVs) for the LFPs between the cortical sites. The CCGs were larger in the pairs separated within 200µm than the pairs separated over 200µm. The main effects of the preferred orientations and the overlap in the receptive field were significant for the CCGs in pairs separated over 200µm, suggesting the importance of relatively long-range horizontal connections on spiking activities. The PLV showed two peaks in the early and late phases of the responses. Both peaks decreased with increased separation of the recording sites and the difference of the preferred orientations. Significant main effects of the separation of the recording sites and the difference of the preferred orientations were found in both peaks, but an interaction effect was significant only in the late phase. The PLV in the late phase may contain information that combines the site separation and their preferred orientations, while the PLV in the early phase may not contain the interaction information.