Lonsbury-Martin B L, Martin G K, Bohne B A
J Acoust Soc Am. 1987 May;81(5):1507-18. doi: 10.1121/1.394503.
The findings of a number of studies investigating the effects of excessive sound on hearing have indicated that the correspondence between behavioral, physiological, and histological measures of noise-induced hearing loss may be markedly dependent upon the sensitivity of the particular measure. Recent studies demonstrating significant changes in the responses of single auditory neurons following brief exposures to pure tones suggest that single-unit activity may be a sensitive indicator of physiological insult to the organ of Corti's sensory cells. In addition, the long-lasting nature of the changes in neural responsiveness suggests that each temporary threshold shift (TTS) episode may produce an increment of damage to the ear that eventually contributes to a measurable permanent threshold shift (PTS). A logical extension of this implication is the proposal that repeated episodes of TTS would first affect single-unit thresholds, and that such damage would eventually manifest itself as PTS. A test of this notion was performed by repeatedly exposing monkeys to short-lasting TTS sounds for many months. Behavioral thresholds were monitored using a reaction-time task before and after each inducement of TTS. Two subjects participated in exposure sessions for 18 months, while the remaining monkey was exposed to identical stimuli for 6 months. At the end of behavioral testing, the monkeys were prepared for chronic recording from single cells of the cochlear nucleus. Following the recording period, cochleas were prepared for examination as plastic-embedded whole mounts. Flat preparations of the cochlear duct were made and the position and extent of damage to the organ of Corti and myelinated nerve fibers were determined. No elevations in behavioral threshold were noted for the monkey receiving 6 months of sound-exposure experience, while for both subjects exposed for 18 months, a significant high-frequency hearing loss became apparent during the final months of exposure. For damaged ears, the thresholds of ipsilateral cochlear nucleus units were elevated for characteristic frequencies (CFs) corresponding to the frequency regions where behavioral thresholds were shifted. Thresholds for units with high-frequency CFs in the animal exposed for 6 months also demonstrated a loss in sensitivity. Histological examination of the cochleas of monkeys with permanent hearing losses revealed corresponding damage to the high-frequency region of the organ of Corti. The monkey exposed for 6 months, which demonstrated only elevated unit thresholds, also had high-frequency lesions.(ABSTRACT TRUNCATED AT 400 WORDS)
多项研究调查了过度噪音对听力的影响，其结果表明，噪声性听力损失的行为学、生理学和组织学测量之间的对应关系可能显著取决于特定测量方法的敏感性。最近的研究表明，在短暂暴露于纯音后，单个听觉神经元的反应会发生显著变化，这表明单个神经元活动可能是对柯蒂氏器官感觉细胞生理损伤的敏感指标。此外，神经反应性变化的长期性质表明，每次暂时阈移（TTS）发作可能会对耳朵造成一定程度的损伤，最终导致可测量的永久性阈移（PTS）。这一观点的合理延伸是，反复出现的TTS发作首先会影响单个神经元的阈值，而这种损伤最终会表现为PTS。为了验证这一观点，研究人员让猴子连续数月反复暴露于短暂的TTS声音中。在每次诱发TTS之前和之后，使用反应时间任务监测行为阈值。两只猴子参与了为期18个月的暴露实验，而另一只猴子则暴露于相同刺激下6个月。在行为测试结束时，对猴子进行准备，以便从耳蜗核的单个细胞进行长期记录。记录期结束后，将耳蜗制成塑料包埋的整体标本进行检查。制作了耳蜗管的扁平标本，并确定了柯蒂氏器官和有髓神经纤维的损伤位置和程度。接受6个月声音暴露实验的猴子，其行为阈值没有升高，而在接受18个月暴露实验的两只猴子中，在暴露的最后几个月出现了明显的高频听力损失。对于受损耳朵，同侧耳蜗核单位的阈值在与行为阈值发生变化的频率区域相对应的特征频率（CF）处升高。在暴露6个月的动物中，具有高频CF的单位的阈值也显示出敏感性丧失。对患有永久性听力损失的猴子的耳蜗进行组织学检查，发现柯蒂氏器官的高频区域有相应损伤。暴露6个月的猴子，仅显示单位阈值升高，也有高频病变。（摘要截断于400字）
