The Human Visual Pathways and Skilled Reading

在大脑中，思想和情绪很大程度上是由皮质神经元处理的，皮质神经元是位于大脑表面的一层薄(3-5毫米)的小细胞。这些神经元结合了来自大脑不同部位的信号。这些神经元的输入和输出，即大脑的线路，就是轴突。一些轴突在神经元之间进行短程连接。它们携带的信号只有十分之几毫米。其他轴突进行远程连接。它们在大脑皮层广泛分离部分的神经元之间传递几厘米长的信号。近年来，人类历史上第一次有可能在活着的人脑中测量远程轴突所走的路径。在美国国家科学基金会的资助下，斯坦福大学的布莱恩·万德尔博士正在开发一种方法，用于非侵入性地测量和识别行进几厘米的轴突所遵循的路径。新方法基于磁共振成像数据和专门的数学算法。本项目正在实施一种数学方法来测试这些方法的精度并提高空间分辨率。这一方法的进步将使进行新的大脑测量成为可能，以识别视觉皮质中携带着观看和阅读所必需的信号的轴突。人们正在进行实验，以识别人类视觉皮质中的所有主要白质纤维束，并具体识别大脑从视觉区域到阅读区域的纤维束。对视觉至关重要的远程连接位于大脑的后部。当我们阅读时，这些视觉信号被传送到大脑的更前部。这些前部区域的神经元解释字母和单词的形状，对于熟练阅读是必不可少的。解决个人阅读途径的能力是触手可及的，包括大脑皮层和轴突。这个项目正在实施新的数学方法来识别个别学科中的这些途径。第一次测量的目的是为了了解对视觉至关重要的远程视觉连接的发展。相关大脑通路的完整接线图和典型生长轨迹的测量将使识别个别儿童的发育异常成为可能，以便他们能够接受适当的干预。这些方法将适用于大脑的许多其他部分，而且有一个广泛传播分析软件的计划。

Thought and emotion are processed in the brain in large part by cortical neurons, small cells located in a thin (3-5mm) sheet on the surface of the brain. These neurons combine signals from different parts of the brain. The inputs and outputs of these neurons, the brain's wiring, are the axons. Some axons make short-range connections between neurons. They carry signals only a few tenths of a millimeter. Other axons make long-range connections. They carry the signals several centimeters between neurons in widely separated parts of cortex. In recent years, for the first time in human history, it has become possible to measure in the living human brain the path traveled by the long-range axons. With funding from the National Science Foundation, Dr. Brian Wandell of Stanford University is developing methods for measuring and identifying, noninvasively, the path followed by axons that travel a few centimeters. The new methods are based on magnetic resonance imaging data and specialized mathematical algorithms. This project is implementing a mathematical method to test the accuracy and improve the spatial resolution of these methods. This methodological advance will make it possible to make new brain measurements to identify the axons in visual cortex that carry the signals essential for seeing and reading. Experiments are being conducted to identify all the major white matter fiber tracts in the human visual cortex and also to identify specifically the tracts from visual to reading areas of the brain.The long-range connections essential for vision are located in the posterior part of the brain. When we read, these visual signals are carried to more anterior parts of the brain. The neurons in these anterior regions interpret the shape of the letters and words, and are essential for skilled reading. The ability to resolve the reading pathways in individuals, including both the cortex and the axons, is within reach. This project is implementing new mathematical methods to identify these pathways in individual subjects. The first measurements are designed to understand the development of the long-range visual connections essential for seeing. A full wiring diagram of the relevant brain pathways and measurements of typical growth trajectories will make it possible to identify developmental abnormalities in individual children so that they can receive appropriate intervention. The methods will be applicable to many other parts of the brain, and there is a plan for wide dissemination of the analysis software.