COMPUTATIONAL MODEL OF SYNAPTIC DEVELOPMENT

因为发展中的皮层反应特性是高度可变的， 这是经验的一个功能，因为突触发生是一个基本的 在发育过程中，我们正在研究突触发生的可能作用 可能会在这种反应特性的改变中发挥作用。因为眼睛 优势是反应属性，已收到最实验 注意，我们的发展模型模拟了各种实验 操纵，做，或不，产生这种反应的变化， 大脑皮层第17区的第IV层细胞。（眼优势是 一个技术术语，描述单个细胞产生的相对细胞放电 对只给予左眼的刺激的反应， 只对右眼进行刺激。如果一个细胞同样快速地 无论是介绍，它被描述为双眼;如果细胞火灾更多 对于一只眼睛而不是另一只眼睛，该单元被描述为单眼的， 更喜欢与较大响应相关联的眼睛）。 我们的目标是找到适应过程的形式，即。 突触发生、突触脱落和联合突触增强 和抑郁症，它们是相互兼容的， 这意味着实验观察的模型。这些模型经过测试 用计算机模拟。这种模拟不仅对 测试视觉发展的理论，也是为了让人们关注 这些问题是实验者凭直觉无法理解的。这样的模型 提高实验研究的效率， 了解大脑发育。 到目前为止，我们已经模拟了在四个 条件：正常环境;单眼剥夺;以及 两种药物治疗单眼剥夺这些模拟 条件显示了单个细胞的响应特性如何随着 时间的函数。这项工作的结果鼓舞了我们，因为我们发现， 响应特性的预期趋势是可以实现的， 使得模型过于复杂，并且因为稳态响应 性能，没有过度的振荡，是可以实现的，即使我们 改变输入统计和/或模拟药物操作。 我们现在建议模拟更多的细胞， 优势直方图需要直方图，因为 单眼和双眼的对比总是定量地精确到 单眼或双眼反应性，即发表的数据在 这类直方图的形式。 在试图理解最简单的模型，适合出版的 直方图，我们将调查各种可能破坏 模型的性能，或者更可能的是，增加 该模型这些变量包括突触的形成 修正方程，阈值函数的作用， 抑制等。调查的一部分也是相互作用的 输入统计;即外侧膝状体活动的特征 会发生变化，当它们变化时，它们会与变量相互作用， 和网络的大小相互作用。

Because developing cortical response properties are highly modifiable as a function of experience and because synaptogenesis is a fundamental process of development, we are studying the possible roles synaptogenesis might play in such modifications of response properties. Because ocular dominance is the response property that has received the most experimental attention, our developmental models simulate the various experimental manipulations that do, or do not, produce changes of this response for layer IV cells of area 17 of the cerebral Cortex. (ocular dominance is the technical term describing the relative cell firing a single cell produces in response to a stimulus given to just the left eye versus the same stimulus given to just the right eye. If a cell fires equally fast to either presentation, it is described as binocular; if the cell fires more for one eye than the other, the cell is described as monocular and preferring the eye associated with the larger response.) Our goal is to find the form of the adaptive processes, i.e. synaptogenesis, synaptic shedding, and associative synaptic potentiation and depression, that are compatible with each other and that together imply a model of the experimental observations. Such models are tested with computer simulations. Such simulations are useful, not only for testing theories of visual development, but also for bringing into focus issues that are not intuitively available to experimentalists. Such models increase both the efficiency of experimental research and our understanding of brain development. So far we have simulated developing ocular dominance under four conditions: a normal environment; monocular deprivation; and the effect of two drug treatments on monocular deprivation. The simulations of these conditions show how the response properties of individual cells change as a function of time. The results of this work encourage us because we find that the desired trends in response properties were achievable without making the model overly complex and because steady-state response properties, without undue oscillations, were achievable even after we altered input statistics and/or simulated drug manipulations. We now propose to simulate many more cells so we can create ocular dominance histograms. Histograms are needed because the dichotomy of monocular versus binocular is always quantitiveIy refined into degrees of monocular or binocular responsiveness, i.e. the published data are in the form of such histograms. In trying to understand the simplest model that fits the published histograms, we will investigate a variety of variables that might destroy the performance of the model or, more likely, increase the robustness of the model. Such variables include the formulation of the synaptic modification equations, the role of threshold functions, the role of inhibition, etc. Also part of the investigation is the interaction of the input statistics; i.e. the characteristics of lateral geniculate activity will be varied, and as they vary, they will interact with the variables just mentioned and interact with the size of the network.