In macaques, the middle lateral auditory cortex (ML) is a belt region adjacent to primary auditory cortex (A1) and believed to be at a hierarchically higher level. Although ML single-unit responses have been studied for several auditory stimuli, the ability of ML cells to encode amplitude modulation (AM) - an ability which has been widely studied in A1 - has not yet been characterized. Here we compared the responses of A1 and ML neurons to amplitude-modulated (AM) noise in awake macaques. While several of the basic properties of A1 and ML responses to AM noise were similar, we found several key differences. ML neurons were less likely to phase lock, did not phase lock as strongly, and were more likely to respond in a non-synchronized fashion than A1 cells, consistent with a temporal-to-rate transformation as information ascends the auditory hierarchy. ML neurons tended to have lower temporally (phase-locking) based best modulation frequencies than A1. Neurons that decreased their firing rate in response to AM noise relative to their firing rate in response to unmodulated noise became more common at the level of ML than they were in A1. In both A1 and ML we found a prevalent class of neurons that usually have enhanced rate responses relative to responses to the unmodulated noise at lower modulation frequencies and suppressed rate responses relative to responses to the unmodulated noise at middle modulation frequencies.

中文翻译：

---

听觉皮层中的幅度调制编码：初级和中侧带区域之间的比较

在猕猴中，中外侧听觉皮层 (ML) 是与初级听觉皮层 (A1) 相邻的带区，据信处于更高的层次。尽管已经针对多种听觉刺激研究了 ML 单单位响应，但 ML 细胞编码幅度调制 (AM) 的能力——一种在 A1 中得到广泛研究的能力——尚未得到表征。在这里，我们比较了 A1 和 ML 神经元对清醒猕猴中调幅 (AM) 噪声的反应。虽然 A1 和 ML 对 AM 噪声响应的几个基本特性相似，但我们发现了几个关键差异。与 A1 细胞相比，ML 神经元不太可能锁相，锁相没有那么强，并且更有可能以非同步方式响应，随着信息上升到听觉层次，与时间到速率的转换一致。ML 神经元的时间（锁相）最佳调制频率往往低于 A1。相对于响应未调制噪声的放电率，降低响应 AM 噪声的放电率的神经元在 ML 水平比在 A1 中更常见。在 A1 和 ML 中，我们发现了一类普遍的神经元，相对于在较低调制频率下对未调制噪声的响应，它们通常具有增强的速率响应，而相对于在中等调制频率下对未调制噪声的响应，速率响应受到抑制。相对于响应未调制噪声的放电率，降低响应 AM 噪声的放电率的神经元在 ML 水平比在 A1 中更常见。在 A1 和 ML 中，我们发现了一类普遍的神经元，相对于在较低调制频率下对未调制噪声的响应，它们通常具有增强的速率响应，而相对于在中等调制频率下对未调制噪声的响应，速率响应受到抑制。相对于响应未调制噪声的放电率，降低响应 AM 噪声的放电率的神经元在 ML 水平比在 A1 中更常见。在 A1 和 ML 中，我们发现了一类普遍的神经元，相对于在较低调制频率下对未调制噪声的响应，它们通常具有增强的速率响应，而相对于在中等调制频率下对未调制噪声的响应，速率响应受到抑制。