Departments of Biomedical Engineering.
Psychology, Behavioral Neuroscience, and.
J Neurosci. 2018 Aug 1;38(31):6967-6982. doi: 10.1523/JNEUROSCI.2871-17.2018. Epub 2018 Jun 28.
Auditory cortex is essential for mammals, including rodents, to detect temporal "shape" cues in the sound envelope but it remains unclear how different cortical fields may contribute to this ability (Lomber and Malhotra, 2008; Threlkeld et al., 2008). Previously, we found that precise spiking patterns provide a potential neural code for temporal shape cues in the sound envelope in the primary auditory (A1), and ventral auditory field (VAF) and caudal suprarhinal auditory field (cSRAF) of the rat (Lee et al., 2016). Here, we extend these findings and characterize the time course of the temporally precise output of auditory cortical neurons in male rats. A pairwise sound discrimination index and a Naive Bayesian classifier are used to determine how these spiking patterns could provide brain signals for behavioral discrimination and classification of sounds. We find response durations and optimal time constants for discriminating sound envelope shape increase in rank order with: A1 < VAF < cSRAF. Accordingly, sustained spiking is more prominent and results in more robust sound discrimination in non-primary cortex versus A1. Spike-timing patterns classify 10 different sound envelope shape sequences and there is a twofold increase in maximal performance when pooling output across the neuron population indicating a robust distributed neural code in all three cortical fields. Together, these results support the idea that temporally precise spiking patterns from primary and non-primary auditory cortical fields provide the necessary signals for animals to discriminate and classify a large range of temporal shapes in the sound envelope. Functional hierarchies in the visual cortices support the concept that classification of visual objects requires successive cortical stages of processing including a progressive increase in classical receptive field size. The present study is significant as it supports the idea that a similar progression exists in auditory cortices in the time domain. We demonstrate for the first time that three cortices provide temporal spiking patterns for robust temporal envelope shape discrimination but only the ventral non-primary cortices do so on long time scales. This study raises the possibility that primary and non-primary cortices provide unique temporal spiking patterns and time scales for perception of sound envelope shape.
听觉皮层对于包括啮齿动物在内的哺乳动物检测声音包络中的时间“形状”线索至关重要，但不同的皮层区域如何可能有助于这种能力仍不清楚（Lomber 和 Malhotra，2008；Threlkeld 等人，2008）。以前，我们发现精确的尖峰模式为大鼠初级听觉（A1）、腹侧听觉区（VAF）和尾侧上丘听觉区（cSRAF）中的声音包络中的时间形状线索提供了潜在的神经编码（Lee 等人，2016）。在这里，我们扩展了这些发现，并描述了雄性大鼠听觉皮层神经元时间精确输出的时间过程。使用成对声音辨别指数和朴素贝叶斯分类器来确定这些尖峰模式如何为行为辨别和声音分类提供大脑信号。我们发现，随着等级的增加，用于辨别声音包络形状的响应持续时间和最佳时间常数增加：A1<VAF<cSRAF。相应地，与 A1 相比，非初级皮层中的持续尖峰更突出，导致声音辨别更稳健。尖峰时间模式对 10 种不同的声音包络形状序列进行分类，当跨神经元群体汇总输出时，性能达到最大值增加了一倍，表明所有三个皮层区域都存在稳健的分布式神经编码。总之，这些结果支持这样一种观点，即来自初级和非初级听觉皮层区域的时间精确尖峰模式为动物提供了辨别和分类声音包络中大量时间形状所需的信号。视觉皮层中的功能层次结构支持这样一种观点，即视觉物体的分类需要连续的皮层处理阶段，包括经典感受野大小的逐渐增加。本研究具有重要意义，因为它支持这样一种观点，即在听觉皮层中也存在类似的时间域进展。我们首次证明，三个皮层为稳健的时间包络形状辨别提供了时间尖峰模式，但只有腹侧非初级皮层在长时间尺度上如此。这项研究提出了一种可能性，即初级和非初级皮层为声音包络形状的感知提供了独特的时间尖峰模式和时间尺度。
