Neural ensemble codes for stimulus periodicity in auditory cortex.
Neural ensemble codes for stimulus periodicity in auditory cortex.
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DOI：
10.1523/jneurosci.5475-09.2010
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发表时间：
2010-04-07
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影响因子：
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通讯作者：
Schnupp JW
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作者：
Bizley JK;Walker KM;King AJ;Schnupp JW
我们测量了雄性和雌性雪貂听觉皮层神经元对不同基频（f0）或周期性的人工元音的反应，并将这些反应与经过训练以区分这些声音周期性的动物的表现进行比较。在所检查的所有五个听觉皮层区域中都发现了对 f0 的敏感性，其中大多数神经元表现出低通或高通响应功能。只有极少数情况下，单个神经元放电的刺激依赖性足以解释雪貂的辨别能力。相比之下，当使用简单的分类器进行分析时，由 3-61 个同时记录的神经元组成的小型整体的反应通常能够像动物一样区分周期性变化。我们研究了解码整体响应的四种潜在策略：尖峰计数、相对首次尖峰延迟、二进制“尖峰或无尖峰”代码和尖峰顺序代码。所有四个代码都有效地代表了刺激周期性，令人惊讶的是，尖峰计数和相对延迟代码在刺激开始后 75 毫秒内实现了同样快速的读出。因此，相对延迟代码不一定有助于更快的判别判断。联合峰值计数加上相对延迟代码比单独的任何一个代码提供更多信息，表明每个测量捕获的信息并非完全冗余。即使刺激强度在 20 dB 范围内随机变化，神经元的响应（而非单个神经元的响应）也能可靠地编码 f0 变化。由于经过训练的动物可以区分不同声音级别的刺激周期性，这意味着集合代码更适合解释行为表现。
We measured the responses of neurons in auditory cortex of male and female ferrets to artificial vowels of varying fundamental frequency (f0), or periodicity, and compared these to the performance of animals trained to discriminate the periodicity of these sounds. Sensitivity to f0 was found in all five auditory cortical fields examined, with most of those neurons exhibiting either low-pass or high-pass response functions. Only rarely was the stimulus dependence of individual neuron discharges sufficient to account for the discrimination performance of the ferrets. In contrast, when analyzed with a simple classifier, responses of small ensembles, comprising 3-61 simultaneously recorded neurons, often discriminated periodicity changes as well as the animals did. We examined four potential strategies for decoding ensemble responses: spike counts, relative first-spike latencies, a binary “spike or no-spike” code and a spike-order code. All four codes represented stimulus periodicity effectively, and, surprisingly, the spike count and relative latency codes enabled an equally rapid readout, within 75 ms of stimulus onset. Thus, relative latency codes do not necessarily facilitate faster discrimination judgments. A joint spike count plus relative latency code was more informative than either code alone, indicating that the information captured by each measure was not wholly redundant. The responses of neural ensembles, but not of single neurons, reliably encoded f0 changes even when stimulus intensity was varied randomly over a 20 dB range. Because trained animals can discriminate stimulus periodicity across different sound levels, this implies that ensemble codes are better suited to account for behavioral performance.