Milner Elliott Scott, Do Michael Tri Hoang
F.M. Kirby Neurobiology Center and Department of Neurology, Boston Children's Hospital and Harvard Medical School, Center for Life Science 12061, Boston, MA 02115, USA; Center for Brain Science, Harvard University, Cambridge, MA 02138, USA.
Cell. 2017 Nov 2;171(4):865-876.e16. doi: 10.1016/j.cell.2017.09.005. Epub 2017 Sep 28.
Environmental illumination spans many log units of intensity and is tracked for essential functions that include regulation of the circadian clock, arousal state, and hormone levels. Little is known about the neural representation of light intensity and how it covers the necessary range. This question became accessible with the discovery of mammalian photoreceptors that are required for intensity-driven functions, the M1 ipRGCs. The spike outputs of M1s are thought to uniformly track intensity over a wide range. We provide a different understanding: individual cells operate over a narrow range, but the population covers irradiances from moonlight to full daylight. The range of most M1s is limited by depolarization block, which is generally considered pathological but is produced intrinsically by these cells. The dynamics of block allow the population to code stimulus intensity with flexibility and efficiency. Moreover, although spikes are distorted by block, they are regularized during axonal propagation.
环境光照强度跨越多个对数单位，其强度变化对于包括昼夜节律时钟调节、觉醒状态和激素水平调节等基本功能至关重要。关于光强度的神经表征以及它如何覆盖所需范围，我们知之甚少。随着对强度驱动功能所必需的哺乳动物光感受器——M1 型内在光敏视网膜神经节细胞（M1 ipRGCs）的发现，这个问题变得可以研究。人们认为 M1 型细胞的动作电位输出在很宽的范围内均匀地跟踪强度。我们给出了不同的理解：单个细胞在狭窄的范围内起作用，但细胞群体能够覆盖从月光到全日照的辐照度范围。大多数 M1 型细胞的范围受到去极化阻滞的限制，这种阻滞通常被认为是病理性的，但却是由这些细胞内在产生的。阻滞的动态过程使细胞群体能够灵活而高效地编码刺激强度。此外，尽管动作电位会因阻滞而失真，但它们在轴突传播过程中会被规范化。
