Magnetoencephalography (MEG) is used in clinical and fundamental studies of brain functions, primarily for the excellent temporal resolution it provides. The spatial resolution is often assumed to be poor, because of the ill-posed nature of MEG source modeling. However, the question of spatial resolution in MEG has seldom been studied in quantitative detail. Here we use the well-known retinotopic organization of the primary visual cortex (V1) as a benchmark for estimating the spatial resolution of MEG source imaging. Using a standard visual stimulation paradigm in human subjects, we find that individual MEG sources exhibit well-delineated visual receptive fields that collectively follow the known mapping of the retinal surface onto the cortex. Based on the size of these receptive fields and the variability of the signal, we are able to resolve MEG signals separated by approximately 7 mm in smooth regions of cortex and less than 1 mm for signals near curved gyri. The maximum resolution is thus comparable to that of the spacing of hypercolumns in human visual cortex. Overall, our results suggest that the spatial resolution of MEG can approach or in some cases exceed that of fMRI.

译文

脑磁图 (MEG) 用于脑功能的临床和基础研究,主要用于其提供的出色的时间分辨率。由于MEG源建模的不适定性质,通常认为空间分辨率较差。但是,很少对MEG中的空间分辨率问题进行定量研究。在这里,我们使用初级视觉皮层 (V1) 的众所周知的视网膜组织作为估计MEG源成像空间分辨率的基准。在人类受试者中使用标准的视觉刺激范例,我们发现单个MEG源表现出轮廓分明的视觉感受野,这些视觉感受野共同遵循视网膜表面在皮层上的已知映射。基于这些感受野的大小和信号的可变性,我们能够解决MEG信号,该信号在皮层的光滑区域中被大约7毫米分开,而对于弯曲回旋附近的信号则小于1毫米。因此,最大分辨率与人类视觉皮层中超列的间距相当。总体而言,我们的结果表明,MEG的空间分辨率可以接近或在某些情况下超过fMRI。

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