Effect of mouth-opening levels on sound field gain in the ear canal.

The human external auditory canal can become deformed when the mandible moves, and this changes the sound field in the external auditory canal. This study measured the sound field gain in the external auditory canal while varying mouth-opening in three levels. The mandible was fixed at the 1/3, the 2/3, and the maximal mouth-opening levels. Seven 65-dB tones of 200, 500, 1000, 2000, 4000, 6000, and 8000 Hz, which are the sound pressure level and frequency range when people are talking at a normal level, were adopted as the sound stimulus to measure sound field gains at 5, 10, 15, and 20 mm to the interior of the external auditory canal. The results show that, with the exception of the 1.25 dB decrease from 12.96 to 11.71 dB at a depth of 5 mm with a stimulus at 8000 Hz, the differences in the sound field gain at the other depths and stimulus frequencies were within 1 dB and were not statistically significant. These results suggest that mouth-opening level has no effect on the measurement of the sound field in the external auditory canal.

Human amygdala activation by the sound produced during dental treatment: A fMRI study.

During dental treatments, patients may experience negative emotions associated with the procedure. This study was conducted with the aim of using functional magnetic resonance imaging (fMRI) to visualize cerebral cortical stimulation among dental patients in response to auditory stimuli produced by ultrasonic scaling and power suction equipment. Subjects (n = 7) aged 23-35 years were recruited for this study. All were right-handed and underwent clinical pure-tone audiometry testing to reveal a normal hearing threshold below 20 dB hearing level (HL). As part of the study, subjects initially underwent a dental calculus removal treatment. During the treatment, subjects were exposed to ultrasonic auditory stimuli originating from the scaling handpiece and salivary suction instruments. After dental treatment, subjects were imaged with fMRI while being exposed to recordings of the noise from the same dental instrument so that cerebral cortical stimulation in response to aversive auditory stimulation could be observed. The independent sample confirmatory t-test was used. Subjects also showed stimulation in the amygdala and prefrontal cortex, indicating that the ultrasonic auditory stimuli elicited an unpleasant response in the subjects. Patients experienced unpleasant sensations caused by contact stimuli in the treatment procedure. In addition, this study has demonstrated that aversive auditory stimuli such as sounds from the ultrasonic scaling handpiece also cause aversive emotions. This study was indicated by observed stimulation of the auditory cortex as well as the amygdala, indicating that noise from the ultrasonic scaling handpiece was perceived as an aversive auditory stimulus by the subjects. Subjects can experience unpleasant sensations caused by the sounds from the ultrasonic scaling handpiece based on their auditory stimuli.

Anthropometry of external auditory canal by non-contactable measurement.

Human ear canals cannot be measured directly with existing general measurement tools. Furthermore, general non-contact optical methods can only conduct simple peripheral measurements of the auricle and cannot obtain the internal ear canal shape-related measurement data. Therefore, this study uses the computed tomography (CT) technology to measure the geometric shape of the ear canal and the shape of the ear canal using a non-invasive method, and to complete the anthropometry of external auditory canal. The results of the study show that the average height and width of ear canal openings, and the average depth of the first bend for men are generally longer, wider and deeper than those for women. In addition, the difference between the height and width of the ear canal opening is about 40% (p < 0.05). Hence, the circular cross-section shape of the earplugs should be replaced with an elliptical cross-section shape during manufacturing for better fitting.

A phantom and in vivo study of mice following an ischemic stroke using sodium MRI.

Sodium is one of the essential indicators of cell viability in vivo. Regarding extant literature, sodium MRI is widely employed for various studies, including research on tumors, strokes, and neurocognition, because it can non-invasively provide data of physiological metabolism in vivo. Currently, strokes are among the 3 leading causes of death worldwide, and can be categorized as hemorrhagic or ischemic. Approximately 70% to 80% of stroke patients experience an ischemic stroke. Although numerous relevant studies have focused on larger animal models, such as rats, cats, and nonhuman primates, literature that employs mice experimental models is scarce. In this study, we conducted sodium MRI on the brains of mice after an ischemic stroke to observe sodium signal variations in the brain following this type of stroke. The findings indicated that the sodium signals in the brain regions affected by stroke were 2.3 times stronger than those in the lateral ventricles.