Nonlinear event-related responses in fMRI
Nonlinear event-related responses in fMRI
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DOI：
10.1002/mrm.1910390109
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发表时间：
1998-01-01
影响因子：
3.3
通讯作者：
Turner, R
中科院分区：
文献类型：
--
作者：
Friston, KJ;Josephs, O;Turner, R
本文提出了一种基于非线性系统辨识，特别是使用沃尔泰拉系列的方法来表征功能磁共振成像中诱发的血流动力学反应。所采用的方法，使人们能够估计沃尔泰拉内核，描述的刺激呈现和随之而来的血液动力学反应之间的关系。沃尔泰拉级数本质上是线性卷积或“平滑”的高阶扩展。“因此，这些内核代表了血液动力学反应函数的非线性特征，可以模拟不同背景下对刺激的反应（在这项工作中，不同的单词呈现率）以及刺激之间的相互作用。反应的非线性成分被证明是统计学上显着的，核估计使用独立的事件相关的功能磁共振成像实验进行验证。这些非线性效应的一个重要表现是由在时间上接近的先前刺激对刺激特异性反应的调制。这意味着在高刺激呈现率下的反应饱和，并且在某些情况下，显示出倒U型行为。这种行为似乎是BOLD效应所特有的（与脑血流量的诱发变化不同），可能代表血液动力学“不应性”。“本文的目的是描述这些结论所依据的理论和技术，并讨论实验设计和分析的含义。
This paper presents an approach to characterizing evoked hemodynamic responses in fMRI based on nonlinear system identification, in particular the use of Volterra series. The approach employed enables one to estimate Volterra kernels that describe the relationship between stimulus presentation and the hemodynamic responses that ensue. Volterra series are essentially high-order extensions of linear convolution or "smoothing." These kernels, therefore, represent a nonlinear characterization of the hemodynamic response function that can model the responses to stimuli in different contexts (in this work, different rates of word presentation) and interactions among stimuli. The nonlinear components of the responses were shown to be statistically significant, and the kernel estimates were validated using an independent event-related fMRI experiment. One important manifestation of these nonlinear effects is a modulation of stimulus-specific responses by preceding stimuli that are proximate in time. This means that responses at high-stimulus presentation rates saturate and, in some instances, show an inverted U behavior. This behavior appears to be specific to BOLD effects (as distinct from evoked changes in cerebral blood flow) and may represent a hemodynamic "refractoriness." The aim of this paper is to describe the theory and techniques upon which these conclusions were based and to discuss the implications for experimental design and analysis.