STRUCTURE/FUNCTION RELATIONSHIPS IN VISUAL CORTEX

本研究的目的是了解视觉信息是如何在外侧膝状核（LGN）及其目标，初级视觉皮层中处理的。重点是改变细胞反应时间的机制，以及如何利用这些时间来产生编码物体运动方向的皮质细胞。在猫的皮层中，神经元在它们的接受野中表现出不同的时间延迟；这种时空（S-T）接受场结构有助于细胞的方向选择性（DS）。LGN造成了大部分的时间延迟；特别是，它产生长时间的延迟，这是皮层细胞在低运动速率下退行性变所必需的。在猫身上的研究揭示了运动分析的基本机制，但它们在多大程度上是普遍的，并在其他物种中起作用，尚不清楚。我们将通过研究猴子大脑中方向选择的神经机制来解决这个问题。具体目的如下：(1)我们将确定皮层细胞的DS如何随刺激运动速率变化，以表征潜在机制的操作范围。(2)将比较单细胞中的S-T接受场结构和方向选择性，以确定S-T结构对DS的贡献及其附加机制。(3)将测量这些感受野不同位置的反应，以揭示这些感受野中存在的时间延迟范围。(4)为了研究这些时间的潜在来源，我们将测量非定向选择性皮层细胞的时间，这些细胞可能是退行性椎体变性细胞的输入。(5)为了确定丘脑输入对皮层反应的潜在贡献，我们将测量LGN中细胞的反应时间和其他特性，并将其与皮层时间进行比较。(6)在皮层中，我们将研究DS调谐、S-T结构和响应时间等特性之间的层流关系，以深入了解潜在的连接关系和方向选择的机制。在整个过程中，我们将确定细胞之间是否存在长延迟，如果存在，延迟是在视觉通路的哪个阶段引入的。这些研究将为灵长类动物的时间处理机制提供新的、关键的见解。更广泛地说，了解大脑如何使用时间信息是很重要的，因为在人类中，时间信号处理的缺陷与一些认知障碍（如阅读障碍）有关。

The goal of this research is to understand how visual information is processed in the lateral geniculate nucleus (LGN) and its target, the primary visual cortex. Emphasis is on mechanisms that alter cells response timings and on how these timings are used to create cortical cells that encode the direction of object motion. In cat cortex, neurons display different timing delays across their receptive fields; this spatiotemporal (S-T) receptive-field structure helps to make the cells direction selective (DS). The LGN creates most of these timing delays; in particular, it generates long delays that are necessary for cortical cells to be DS at low rates of motion. Work in the cat has revealed basic mechanisms of motion analysis, but the extent to which they are universal, and operate in other species, is not known. We will address this issue by examining neural mechanisms of direction selectivity in the brain of the monkey. Specific aims are as follows: (1) We will determine how DS in cortical cells varies with the rate of stimulus motion, to characterize the operating range of underlying mechanisms. (2) S-T receptive-field structure and direction selectivity will be compared in single cells to determine the contribution of S-T structure, and additional mechanisms, to DS. (3) Responses in different positions of these receptive fields will be measured to reveal the range of timing delays present in the fields. (4) To investigate the potential sources of these timings we will measure the timings of nondirection-selective cortical cells that are likely inputs to the DS cells. (5) To determine the potential contribution of thalamic inputs to the cortical responses we will measure response timings and other properties of cells in the LGN and compare them to the cortical timings. (6) In cortex, we will examine laminar relationships among properties such as DS tuning, S-T structure, and response timing to gain insights into potential connectional relationships and mechanisms that underlie direction selectivity. Throughout, we will determine whether long delays exist among cells, if so, at what stage in the visual pathway the delays are introduced. These studies will provide new, critical insights into temporal processing mechanisms in primates. More broadly, understanding how the brain uses timing information is important because, in humans, deficits in temporal signal processing are linked to some cognitive disorders such as dyslexia.