STRUCTURE/FUNCTION RELATIONSHIPS IN VISUAL CORTEX

本研究的目的是了解视觉信息在外侧膝状体核（LGN）及其靶区初级视皮层中的加工过程。 重点是改变细胞反应时间的机制，以及如何使用这些时间来创建编码物体运动方向的皮层细胞。 在猫皮层，神经元在其感受野中显示不同的时间延迟;这种时空（S-T）感受野结构有助于使细胞具有方向选择性（DS）。 LGN产生了大部分的时间延迟;特别是，它产生了长时间的延迟，这是皮质细胞在低运动速率下必须的。 对猫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，还不清楚。 我们将通过研究猴子大脑中方向选择性的神经机制来解决这个问题。具体目标如下：（1）我们将确定皮层细胞中的DS如何随刺激运动的速率而变化，以表征潜在机制的操作范围。 (2)将在单个细胞中比较S-T感受场结构和方向选择性，以确定S-T结构和其他机制对DS的贡献。 (3)将测量这些感受野不同位置的反应，以揭示场中存在的时间延迟的范围。 (4)为了研究这些时间的潜在来源，我们将测量可能输入DS细胞的非方向选择性皮层细胞的时间。 (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，并将它们与皮层时间进行比较。(6)在皮层，我们将检查层之间的关系，如DS调谐，S-T结构，和响应时间的属性，以获得深入了解潜在的连接关系和机制的基础方向选择性。 在整个过程中，我们将确定细胞之间是否存在长时间的延迟，如果是这样，在视觉通路的哪个阶段引入延迟。这些研究将为灵长类动物的时间加工机制提供新的、重要的见解。 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有关，如阅读障碍。

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.