Deficits in auditory and visual processing are commonly encountered by older individuals. In addition to the relatively well described age-associated pathologies that reduce sensory processing at the level of the cochlea and eye, multiple changes occur along the ascending auditory and visual pathways that further reduce sensory function in each domain. One fundamental question that remains to be directly addressed is whether the structure and function of the central auditory and visual systems follow similar trajectories across the lifespan or sustain the impacts of brain aging independently. The present study used diffusion magnetic resonance imaging and electrophysiological assessments of auditory and visual system function in adult and aged macaques to better understand how age-related changes in white matter connectivity at multiple levels of each sensory system might impact auditory and visual function. In particular, the fractional anisotropy (FA) of auditory and visual system thalamocortical and interhemispheric corticocortical connections was estimated using probabilistic tractography analyses. Sensory processing and sensory system FA were both reduced in older animals compared with younger adults. Corticocortical FA was significantly reduced only in white matter of the auditory system of aged monkeys, while thalamocortical FA was lower only in visual system white matter of the same animals. Importantly, these structural alterations were significantly associated with sensory function within each domain. Together, these results indicate that age-associated deficits in auditory and visual processing emerge in part from microstructural alterations to specific sensory white matter tracts, and not from general differences in white matter condition across the aging brain.

SIGNIFICANCE STATEMENT Age-associated deficits in sensory processing arise from structural and functional alterations to both peripheral sensory organs and central brain regions. It remains unclear whether different sensory systems undergo similar or distinct trajectories in function across the lifespan. To provide novel insights into this question, this study combines electrophysiological assessments of auditory and visual function with diffusion MRI in aged macaques. The results suggest that age-related sensory processing deficits in part result from factors that impact the condition of specific white matter tracts, and not from general decreases in connectivity between sensory brain regions. Such anatomic specificity argues for a framework aimed at understanding vulnerabilities with relatively local influence and brain region specificity.

老年人通常会遇到听觉和视觉处理缺陷。除了相对充分描述的与年龄相关的病理学（减少耳蜗和眼睛水平的感觉处理）之外，沿上行听觉和视觉通路发生多种变化，进一步减少每个域的感觉功能。有待直接解决的一个基本问题是，中枢听觉和视觉系统的结构和功能在整个生命周期中是否遵循相似的轨迹，或者独立地承受大脑衰老的影响。本研究使用扩散磁共振成像和电生理学评估成年和老年猕猴的听觉和视觉系统功能，以更好地了解每个感觉系统多个层面的白质连接的年龄相关变化如何影响听觉和视觉功能。特别是，使用概率纤维束成像分析来估计听觉和视觉系统丘脑皮质和半球间皮质连接的分数各向异性（FA）。与年轻人相比，老年动物的感觉处理和感觉系统 FA 均减少。皮质 FA 仅在老年猴子的听觉系统白质中显着降低，而丘脑皮质 FA 仅在同一动物的视觉系统白质中较低。重要的是，这些结构改变与每个域内的感觉功能显着相关。 总之，这些结果表明，与年龄相关的听觉和视觉处理缺陷部分是由于特定感觉白质束的微观结构改变引起的，而不是由于衰老大脑中白质状况的普遍差异。

意义声明 与年龄相关的感觉处理缺陷是由周围感觉器官和中枢大脑区域的结构和功能改变引起的。目前尚不清楚不同的感觉系统在整个生命周期中是否经历相似或不同的功能轨迹。为了对这个问题提供新的见解，这项研究将老年猕猴的听觉和视觉功能的电生理学评估与扩散磁共振成像结合起来。结果表明，与年龄相关的感觉处理缺陷部分是由于影响特定白质束状况的因素造成的，而不是由于感觉脑区域之间的连接性普遍下降所致。这种解剖学的特殊性主张建立一个旨在理解具有相对局部影响和大脑区域特异性的脆弱性的框架。