School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, USA.
Proc Natl Acad Sci U S A. 2011 Sep 6;108(36):14956-61. doi: 10.1073/pnas.1103168108. Epub 2011 Aug 22.
From the perspective of neural coding, the considerable trial-to-trial variability in the responses of neurons to sensory stimuli is puzzling. Trial-to-trial response variability is typically interpreted in terms of "noise" (i.e., it represents either intrinsic noise of the system or information unrelated to the stimuli). However, trial-to-trial response variability can be considerably different across stimuli, suggesting that it could also provide an important contribution to the information conveyed by the neural responses about the stimuli. To test this hypothesis, we addressed the problem of discriminating stimulus location from the spike-count responses of neurons recorded in the ventro-postero-medial (VPM) nucleus of the thalamus in anesthetized rats. Using a recently developed information theory approach, we verified that differences between stimuli in the trial-to-trial spike-count variability of the responses provided an important contribution to the overall information carried by the neurons. In addition, we found that the relatively reliable (sub-Poisson) firing regime of our VPM neurons was not only more informative, but also more redundant between neurons compared with a more variable (Poisson) firing regime with the same total number of spikes. The typical increase in trial-to-trial response variability from the periphery to the cortex could therefore serve as a strategy to reduce redundancy between neurons and promote efficient sparse coding distributed in large populations of neurons. Overall, our data suggest that the trial-to-trial response variability plays a critical role in establishing the trade-off between total information and redundancy between neurons in population codes.
从神经编码的角度来看，神经元对感觉刺激的反应在试验间存在相当大的可变性，这令人费解。试验间的反应可变性通常被解释为“噪声”（即，它代表系统的固有噪声或与刺激无关的信息）。然而，试验间的反应可变性在不同的刺激之间可能有很大的不同，这表明它也可以为神经反应所传达的关于刺激的信息提供重要贡献。为了检验这一假设，我们解决了从麻醉大鼠丘脑腹后内侧核（VPM）记录的神经元的尖峰计数反应中区分刺激位置的问题。使用最近开发的信息论方法，我们验证了刺激间反应尖峰计数可变性的差异为神经元携带的整体信息提供了重要贡献。此外，我们发现，与具有相同总尖峰数的更可变（泊松）放电模式相比，我们的 VPM 神经元的相对可靠（亚泊松）放电模式不仅更具信息量，而且神经元之间的冗余性也更低。因此，从外围到皮层的试验间反应可变性的典型增加可以作为一种策略，以减少神经元之间的冗余，并促进在大量神经元中分布的高效稀疏编码。总的来说，我们的数据表明，试验间的反应可变性在建立群体编码中神经元之间的总信息量和冗余之间的权衡中起着关键作用。
