CUNY Graduate Center, New York, New York, United States of America.
Department of Neurobiology and Behavior, Stony Brook University, Stony Brook, New York, United States of America.
PLoS Biol. 2022 Oct 21;20(10):e3001803. doi: 10.1371/journal.pbio.3001803. eCollection 2022 Oct.
Brain asymmetry in the sensitivity to spectrotemporal modulation is an established functional feature that underlies the perception of speech and music. The left auditory cortex (ACx) is believed to specialize in processing fast temporal components of speech sounds, and the right ACx slower components. However, the circuit features and neural computations behind these lateralized spectrotemporal processes are poorly understood. To answer these mechanistic questions we use mice, an animal model that captures some relevant features of human communication systems. In this study, we screened for circuit features that could subserve temporal integration differences between the left and right ACx. We mapped excitatory input to principal neurons in all cortical layers and found significantly stronger recurrent connections in the superficial layers of the right ACx compared to the left. We hypothesized that the underlying recurrent neural dynamics would exhibit differential characteristic timescales corresponding to their hemispheric specialization. To investigate, we recorded spike trains from awake mice and estimated the network time constants using a statistical method to combine evidence from multiple weak signal-to-noise ratio neurons. We found longer temporal integration windows in the superficial layers of the right ACx compared to the left as predicted by stronger recurrent excitation. Our study shows substantial evidence linking stronger recurrent synaptic connections to longer network timescales. These findings support speech processing theories that purport asymmetry in temporal integration is a crucial feature of lateralization in auditory processing.
大脑对频谱和时间调制的敏感性的不对称性是一种既定的功能特征，它是言语和音乐感知的基础。左听觉皮层（ACx）被认为专门处理言语声音的快速时间成分，而右 ACx 则处理较慢的成分。然而，这些偏侧化的频谱和时间过程背后的电路特征和神经计算仍知之甚少。为了回答这些机制问题，我们使用了一种动物模型——老鼠，该模型捕捉到了人类交流系统的一些相关特征。在这项研究中，我们筛选了可能支持左、右 ACx 之间时间整合差异的电路特征。我们绘制了所有皮层层中主要神经元的兴奋性输入，并发现右 ACx 的浅层比左 ACx 具有更强的递归连接。我们假设潜在的递归神经动力学将表现出与半球专业化相对应的不同特征时间尺度。为了进行研究，我们从清醒的老鼠中记录了尖峰活动，并使用一种统计方法估计了网络时间常数，该方法结合了来自多个弱信噪比神经元的证据。我们发现，正如更强的递归兴奋所预测的那样，右 ACx 的浅层具有比左 ACx 更长的时间整合窗口。我们的研究提供了大量证据，将更强的递归突触连接与更长的网络时间尺度联系起来。这些发现支持了言语处理理论，即时间整合的不对称性是听觉处理中侧化的一个关键特征。
