碩士 / 國立成功大學 / 生理學研究所 / 103 / While acoustic reflexes to loud sounds are well studied (viz., startle, head orienting, pinna, and vibrissa freezing responses), those to soft sounds remain unknown. Tinnitus, a leading hearing disorder, typically affects low intensity hearing (i.e., phantom sound perception of 〈30 dB SPL). Here we speculate that low-intensity acoustic reflexes, if in existence, could reflect the phenomenon of masking (or hearing loss) that accompanies tinnitus. The prevailing theory of tinnitus is that an initial hearing loss leads to an increased central gain to compensate the impaired intensity coding, with the unwanted side-effect of a phantom sound percept (tinnitus) and hyperacusis. The phantom sound produces a masking effect (or hearing loss) of soft sounds perceived similar to the tinnitus percept. Based on such masking, experimental tinnitus is assessed with either the traditional polydypsia avoidance or the more recent prepulse inhibition of acoustic startle reflex. These two methods have shortcomings like (a) time-consuming behavioral training or (b) the use of loud sound stimuli, hence inappropriate for studying the low level hearing in tinnitus. Methods that are simple and objective to estimate low intensity hearing are therefore in demand. Here, we developed a behavioral setup equipped with a digital imaging system designed to detect in awake rats the acoustic reflexes induced by soft sounds. Custom-made software was written to quantify the subtle body movements by optimizing the region of interest in the rat images. We found that for a normal rat, following the sudden presentation of a soft sound, its regular breathing pattern showed occasional perturbations. The perturbation in breathing was identified as an arrest in the respiratory-driven regular displacement of chest or abdomen. We coined this response the ‘acoustic perturbation of breathing (APB)’. We also found that not all sounds we tested had the same effectiveness in inducing APB: e.g., the rubbing sound was the most effective among three tested stimuli. The rubbing sound was therefore adopted as the stimulus for this study. Before the experiment, rats in the exposed group were first exposed during their early life (postnatal week-4) to a moderate level tone (4 kHz, 65 dB SPL, 8 hrs/day). From the previous studies of this laboratory, the same sound-exposure has led to enlarged neurons in the auditory cortex, midbrain and the descending system, consistent with the presence of tinnitus. Compared with other tinnitus-models (e.g., loud sound exposure, salicylate overdose), this early sound-exposure mode, apart from other accompanying neural plasticity, is likely closer to the human case as most tinnitus occurs with senility (likely due to, among other factors, the life-long sound exposure at moderate levels). APB in early sound-exposed rats was depressed when compared with the control, while other acoustic reflexes were not. We interpret this finding in the exposed animals as a masking of low intensity hearing likely associated with tinnitus. We conclude that the APB (reported here for the first time) is useful for assessing low intensity hearing loss associated with tinnitus.
| Identifer | oai:union.ndltd.org:TW/103NCKU5116004 |
| Date | January 2015 |
| Creators | Ta-WeiShen, 沈大為 |
| Contributors | Paul Wai-Fung Poon, 潘偉豐 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 83 |
Page generated in 0.0015 seconds