Neurophysiology of the Fovea

人类和其他灵长类动物的大多数有意识视觉始于中心凹，这是中央的一种特化 视网膜对图像进行了极其详细的编码。中央凹的视锥感光器是为高眼压量身定做的 空间敏锐度。它们具有微小的横截面和致密的堆积，使它们能够形成极其精细的像素 数组。中心凹锥体也延伸出长轴突，使下游细胞从光线的侧面移位。 路径，提供对可视图像的直接访问。中心凹的每个主要输出神经元--侏儒 视网膜神经节细胞(RGC)-也是由单个视锥驱动，保持空间分辨率。相比之下，圆锥体 外周视网膜的部分很宽，分布很广，位于细胞体和突起的层后面； 此外，十几个外围锥体汇聚在单个侏儒RGC上，进一步缩小了空间 决议。中心凹的这些解剖学特化已经被认识了几十年。最重要的是 这一建议的假设是，中心凹视锥细胞也具有高敏感度视力的功能特化。 事实上，最近的一份出版物已经表明，中心凹的光传导时间比外周更长。 圆锥体。这种区别的后果尚不清楚。这在很大程度上取决于光的反应如何 中心凹锥体是由电压门控离子通道(VGIC)在光传导下游形成的。 目标1中提出的实验验证了VGICs补充中心凹不同动力学的假设 光转导。编码精细空间细节的能力还取决于信噪比。实现 高信号/噪声似乎对中央视锥特别重要，因为中央视锥几乎没有机会集中它们的 提高中心凹侏儒视网膜节细胞反应保真度的信号。在目标2中，我们测试了这样的假设 中心凹视锥的信号/噪声在多个阶段增加，包括由 光传导和VGICs及其对胞体和突触膜电压的影响 终点站。对于这两个目标，我们的主要方法是将膜片钳电生理学应用于中心凹和 镶嵌在视网膜回路中的外周视锥细胞或已明显分散成单个细胞。 这些实验还得到了计算建模的补充。我们维持着一个实验平台， 为我们提供用于定量分析的中心凹和周围组织。这里提出的工作构成了 在细胞神经生理学水平上全面了解中心凹的早期步骤。

Most conscious vision in humans and other primates begins with the fovea, a specialization of the central retina that encodes the image in exceptional detail. The cone photoreceptors of the fovea are tailored for high spatial acuity. They have a tiny cross-section and dense packing, allowing them to form an extremely fine pixel array. Foveal cones also extend long axons that allow downstream cells to be displaced laterally from the light path, providing direct access to the visual image. Each of the principal output neurons of the fovea—the midget retinal ganglion cells (RGCs)—is also driven by a single cone, preserving spatial resolution. By contrast, cones of the peripheral retina are broad, widely spaced, and positioned behind layers of cell bodies and processes; additionally, more than a dozen peripheral cones converge upon single midget RGCs, further reducing spatial resolution. These anatomical specializations of the fovea have been recognized for decades. The overarching hypothesis of this proposal is that foveal cones also possess functional specializations for high-acuity vision. Indeed, a recent publication has indicated that phototransduction is more prolonged in foveal than peripheral cones. The consequences of this distinction are not yet clear. Much depends on how the light responses of foveal cones are shaped downstream of phototransduction, by voltage-gated ion channels (VGICs). Experiments proposed in Aim 1 test the hypothesis that VGICs complement the distinct kinetics of foveal phototransduction. The ability to encode fine spatial detail also depends on the signal/noise ratio. Achieving high signal/noise would appear especially important for foveal cones, which have little opportunity to pool their signals to improve the response fidelity of foveal midget RGCs. In Aim 2, we test the hypothesis that the signal/noise of foveal cones is increased at multiple stages, including the currents produced by phototransduction and VGICs as well as their effect on the membrane voltage at the soma and synaptic terminal. For both aims, our principal approach is to apply patch-clamp electrophysiology to foveal and peripheral cones that are embedded within retinal circuitry or have been acutely dispersed into single cells. These experiments are complemented by computational modeling. We maintain an experimental platform that supplies us with foveal and peripheral tissue for quantitative analysis. The work proposed here constitutes early steps toward a full understanding of the fovea at the level of cellular neurophysiology.