Adaptation to Unilateral Hearing Loss in Humans: Cortical and Perceptual Effects

描述（由申请人提供）：该项目的目的是增加对成人周围性听力损失后人类听觉皮层适应的理解。已经研究了两种类型的皮层适应听力：在听力急剧下降的边缘，皮层表现频率的扩大；在单侧耳聋的情况下，通常的皮层侧化模式（更多的是对侧活动而不是同侧活动）的减少。我们使用功能性磁共振成像（fMRI）和心理声学任务研究了两名单耳倾斜性听力损失和另一只耳正常听力的个体的皮质适应与感知能力之间的关系。与受损的耳朵相比，两个人在听到正常耳朵听到的声音时，听觉皮层的侧化活动都有所减少。在刺激正常耳后，侧化程度的降低可归因于同侧皮质激活的增加，并且在受损耳中听力缺失的频率和听力完全保留的频率都可以观察到，这是听力学标准所指示的。我们研究的患者在两种双耳听力任务中发现了感知变化的证据，其中一只耳朵呈现信号，另一只耳朵呈现干扰声音。即使在两个耳朵的听力灵敏度相等的频率下，呈现给受损耳朵的信号的表现更容易受到正常耳朵的干扰，反之亦然。综上所述，fMRI结果和心理声学结果提供了成年人皮层适应和感知功能之间令人信服的相似之处。该项目使用功能磁共振成像进一步确定单侧听力障碍患者长期神经适应的性质和程度，并使用心理声学实验来确定与皮层适应相关的感知变化的性质。加深对皮层对感觉丧失的长期适应的理解，有可能为了解学习过程如何受到发育过程中形成的神经连接模式和成熟动物神经生长限制的限制提供见解。对皮层适应的进一步了解也有可能揭示更高水平的神经过程如何影响恢复（或部分恢复）失去的感觉输入的干预措施的益处和局限性。

DESCRIPTION (provided by applicant): The goal of this project is to increase understanding of adaptation in human auditory cortex after peripheral hearing loss in adults. Two types of cortical adaptation have been studied for hearing: expansion of cortical representation for the frequency that is at the edge of a sharply-sloping hearing loss and a reduction in the usual pattern of cortical lateralization (more contralateral than ipsilateral activity) in cases of unilateral deafness. We have used functional magnetic resonance imaging (fMRI) and psychoacoustic tasks to investigate the relationship between cortical adaptation and perceptual ability in two individuals with a sloping hearing loss in one ear and normal hearing in the other ear. Both individuals showed reduced lateralization of activity in auditory cortex in response to sounds heard in their normal ear as compared to their impaired ear. Reduced lateralization after stimulation of the normal ear was attributable to an increase in ipsilateral cortical activation and was observed both at frequencies where hearing was absent in the impaired ear and also where it was fully preserved as indicated by audiometric criteria. Evidence of perceptual changes in the patients that we studied was found in two binaural listening tasks where a signal was presented in one ear and a distractor sound in the other. Performance on signals presented to the impaired ear was more susceptible to interference from the normal ear than vice versa even at frequencies where audiometric sensitivity in the two ears was equivalent. Together, the fMRI results and psychoacoustic results provide a compelling parallel between cortical adaptation and perceptual function in adult humans. This project uses fMRI to determine further the nature and extent of long-term neural adaptation in individuals with unilateral hearing impairment, and psychoacoustic experiments to determine the nature of the perceptual changes that are associated with cortical adaptation. Increased understanding of long-term cortical adaptation to sensory loss has the potential to provide insight into how processes of learning are constrained both by patterns of neural connectivity created during development and by the limitations on neural growth in mature animals. Increased understanding of cortical adaptation also has the potential to shed light on how higher-level neural processes influence the benefits and limitations of interventions that restore (or partially restore) lost sensory input.