Selecting forward models for MEG source-reconstruction using model-evidence
Selecting forward models for MEG source-reconstruction using model-evidence
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DOI：
10.1016/j.neuroimage.2009.01.062
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发表时间：
2009-05-15
期刊：
影响因子：
5.7
通讯作者：
Friston, K. J.
中科院分区：
文献类型：
--
作者：
Henson, R. N.;Mattout, J.;Friston, K. J.
我们研究了四个关键方面的正向模型的分布式解决方案的脑磁图逆问题：1）本质的皮质网格约束源（源自个人的MRI，或从模板网格逆标准化）; 2）使用单球体、重叠球体或边界元模型（BEM）头部模型; 3）皮质网格的密度（3000与7000个顶点）;以及4）源方向是否被约束为垂直于该网格。这些进行了比较的背景下，两种类型的空间之前的来源：一个单一的先验对应于一个标准的L2-最小范数（MNM）反演，或多个稀疏先验（MSP）。由此产生的生成模型进行了比较，使用自由能近似贝叶斯模型的证据后，拟合多个时代的反应，面对或混乱的面孔。在9名参与者中进行的自由能统计测试显示，MSP模型明显优于MNM模型;前者重建了更深的来源。此外，1）没有证据表明单独定义的皮质网格上级逆归一化的规范网格，但2）明确的证据表明，BEM上级球形头部模型，前提是使用单独定义的内颅骨和头皮网格。最后，对于MSP模型，有证据表明3）较高密度的皮质网格和4）偶极子约束为垂直于网格的组合上级较低密度或自由取向的源（与自由取向是最佳的MNM模型相反）。这些结果具有实际意义的MEG源重建，特别是在组研究的背景下。皇冠版权所有（C）2009由爱思唯尔公司出版。All rights reserved.
We investigated four key aspects of forward models for distributed solutions to the MEG inverse problem: 1) the nature of the cortical mesh constraining sources (derived from an individual's MRI, or inverse-normalised from a template mesh); 2) the use of single-sphere, overlapping spheres, or Boundary Element Model (BEM) head-models; 3) the density of the cortical mesh (3000 vs. 7000 vertices); and 4) whether source orientations were constrained to be normal to that mesh. These were compared within the context of two types of spatial prior on the sources: a single prior corresponding to a standard L2-minimum-norm (MNM) inversion, or multiple sparse priors (MSP). The resulting generative models were compared using a free-energy approximation to the Bayesian model-evidence after fitting multiple epochs of responses to faces or scrambled faces. Statistical tests of the free-energy, across nine participants, showed clear superiority of MSP over MNM models; with the former reconstructing deeper sources. Furthermore, there was 1) no evidence that an individually-defined cortical mesh was superior to an inverse-normalised canonical mesh, but 2) clear evidence that a BEM was superior to spherical head-models, provided individually-defined inner skull and scalp meshes were used. Finally, for MSP models, there was evidence that the combination of 3) higher density cortical meshes and 4) dipoles constrained to be normal to the mesh was superior to lower-density or freely-oriented sources (in contrast to the MNM models, in which free-orientation was optimal). These results have practical implications for MEG source reconstruction, particularly in the context of group studies. Crown Copyright (C) 2009 Published by Elsevier Inc. All rights reserved.