Photoreceptor Signaling in the Early Visual System

描述（由申请人提供）：为了了解我们如何感知颜色，有必要了解我们的视网膜如何从入射光通量中产生视觉信号。已知3种类型的视锥光感受器是任何颜色信号的起点。视锥细胞对光的反应传递到视网膜神经节细胞，它们的轴突离开眼睛向丘脑提供输入，丘脑又向初级视觉皮层（V1）发送信号。目前，有两个持久的争议，在感受野的神经元的颜色结构沿着这一点， 通路其中一个争议是关于中央凹附近的视网膜神经节细胞的侏儒类。目前还不确定这些神经节细胞是否在其感受野中心仅接受来自单一锥型或混合锥型的输入。这两个选项导致视觉系统在这个阶段的不同颜色编码方案，从而限制了颜色在后期阶段的处理方式。由于侏儒神经节细胞约占视网膜输出的80%，因此确定其真正的信号特性至关重要。第二个争议集中在V1中的颜色信号。在这里，V1神经元对视锥细胞特异性刺激的敏感程度也不清楚，部分困难是由于视网膜输入的不确定性引起的。 解决这些问题的主要障碍是无法在体内识别和刺激视网膜中的各个视锥细胞。这项建议的目标是采用一种新开发的视网膜显微镜，克服这些障碍。该仪器可以成像活体眼睛中的视锥细胞，并且可以用彩色光选择性地和重复地刺激单个视锥细胞。我们首先建议验证锥可以映射他们的光谱灵敏度在人类中，使用心理物理技术。使用的刺激参数，使锥身份获得，我们接下来建议映射生理锥字段提供输入到单个神经元的视觉丘脑的三色灵长类动物。在视锥细胞大小的刺激下，丘脑神经元基本上从单个视网膜神经节细胞接收输入;因此， 将了解神经节细胞感受野中心是由纯锥型还是混合锥型组成。我们将集中在中央凹丘脑神经元接收输入的侏儒视网膜神经节细胞类。最后，我们建议映射V1神经元的锥域，以确定其锥域特定输入的强度。我们将从组织学上确认这些神经元的位置 在视觉皮层中，了解它们在V1的已知解剖回路中的位置。我们的研究结果将提供第一个直接映射锥场在体内，并提高我们的理解如何感光细胞信号处理的神经元subserving中央凹视觉。

DESCRIPTION (provided by applicant): To understand how we perceive color, it is necessary to learn how our retina creates visual signals from the incoming flux of light. It is known that 3 types of cone photoreceptors are the starting point for any color signals. The cone responses to light are passed to retinal ganglion cells, and their axons leave the eye to provide input to the thalamus, which in turn sends signals to primary visual cortex (V1). Currently, there are two persistent controversies over the chromatic structure of the receptive fields of neurons along this pathway. One controversy concerns the midget class of retinal ganglion cells near the fovea. It is uncertain if these ganglion cells receive input from only single cone types, or from mixed cone types, in their receptive field centers. The two options lead to different color coding schemes at this stage of the visual system, and thus constrain how color is processed at later stages. Because the midget ganglion cells comprise about 80% of the output from the retina, it is crucial to work out their true signaling properties. The second controversy centers on color signaling in V1. Here, it has also been unclear how sensitive are V1 neurons to cone-specific stimuli, and the difficulty has been, in part, inherited from problems associated with uncertainties in the retinal input. The main impediments to solving these problems have been the inability to identify and stimulate individual cones in the retina in vivo. The goal of this proposal is to employ a newly developed retinal microscope that overcomes these hurdles. The instrument can image the cones in a living eye, and can stimulate single cones selectively and repeatably with colored lights. We first propose to verify that cones can be mapped by their spectral sensitivity in humans, using psychophysical techniques. Using the stimulation parameters that allow cone identities to be obtained, we next propose to map physiologically the cone fields that provide input to single neurons in the visual thalamus of a trichromatic primate. With cone-sized stimulation, thalamic neurons receive input essentially from single retinal ganglion cells; thus we will learn whether ganglion cell receptive field centers are composed of pure or mixed cone types. We will focus on foveal thalamic neurons that receive input from the midget retinal ganglion cell class. Finally, we propose to map the cone fields of V1 neurons, to determine the strength of their cone-specific input. We will confirm histologically the location of these neurons in visual cortex, to learn where they are situated within the known anatomical circuits of V1. Our results will afford the first direct mapping of cone fields in vivo, and improve our understanding of how photoreceptor signals are processed by neurons subserving foveal vision.