School of Communication Sciences & Disorders, University of Memphis, Memphis, TN, USA; Institute for Intelligent Systems, University of Memphis, Memphis, TN, USA; University of Tennessee Health Sciences Center, Department of Anatomy and Neurobiology, Memphis, TN, USA.
School of Communication Sciences & Disorders, University of Memphis, Memphis, TN, USA.
Hear Res. 2019 Oct;382:107795. doi: 10.1016/j.heares.2019.107795. Epub 2019 Aug 27.
Speech-in-noise (SIN) comprehension deficits in older adults have been linked to changes in both subcortical and cortical auditory evoked responses. However, older adults' difficulty understanding SIN may also be related to an imbalance in signal transmission (i.e., functional connectivity) between brainstem and auditory cortices. By modeling high-density scalp recordings of speech-evoked responses with sources in brainstem (BS) and bilateral primary auditory cortices (PAC), we show that beyond attenuating neural activity, hearing loss in older adults compromises the transmission of speech information between subcortical and early cortical hubs of the speech network. We found that the strength of afferent BS→PAC neural signaling (but not the reverse efferent flow; PAC→BS) varied with mild declines in hearing acuity and this "bottom-up" functional connectivity robustly predicted older adults' performance in a SIN identification task. Connectivity was also a better predictor of SIN processing than unitary subcortical or cortical responses alone. Our neuroimaging findings suggest that in older adults (i) mild hearing loss differentially reduces neural output at several stages of auditory processing (PAC > BS), (ii) subcortical-cortical connectivity is more sensitive to peripheral hearing loss than top-down (cortical-subcortical) control, and (iii) reduced functional connectivity in afferent auditory pathways plays a significant role in SIN comprehension problems.
老年人在噪声环境下的言语理解能力下降与皮质下和皮质听觉诱发电位的变化有关。然而，老年人理解噪声下言语的困难也可能与脑干和听觉皮层之间信号传输（即功能连接）的不平衡有关。通过对脑干（BS）和双侧初级听觉皮层（PAC）源的言语诱发电位进行高密度头皮记录建模，我们发现，除了减弱神经活动外，老年人的听力损失还会损害言语网络的皮质下和早期皮质中枢之间的言语信息传输。我们发现，传入 BS→PAC 的神经信号强度（而不是传出的 PAC→BS 信号）随听力敏度的轻微下降而变化，这种“自上而下”的功能连接可以很好地预测老年人在噪声下言语识别任务中的表现。与单一的皮质下或皮质反应相比，连接性也是 SIN 处理的更好预测指标。我们的神经影像学研究结果表明，在老年人中：（i）轻度听力损失会在听觉处理的多个阶段（PAC>BS）不同程度地降低神经输出；（ii）皮质下-皮质连接性对周围听力损失比自上而下（皮质下-皮质）控制更敏感；（iii）传入听觉通路的功能连接减少在 SIN 理解问题中起着重要作用。
