Department of Physiology, Anatomy and Genetics, University of Oxford Oxford, UK.
Nuffield Department of Clinical Neuroscience, FMRIB Centre, John Radcliffe Hospital, University of Oxford Oxford, UK.
Front Neurosci. 2014 May 27;8:127. doi: 10.3389/fnins.2014.00127. eCollection 2014.
Magnetoencephalography (MEG) allows the physiological recording of human brain activity at high temporal resolution. However, spatial localization of the source of the MEG signal is an ill-posed problem as the signal alone cannot constrain a unique solution and additional prior assumptions must be enforced. An adequate source reconstruction method for investigating the human visual system should place the sources of early visual activity in known locations in the occipital cortex. We localized sources of retinotopic MEG signals from the human brain with contrasting reconstruction approaches (minimum norm, multiple sparse priors, and beamformer) and compared these to the visual retinotopic map obtained with fMRI in the same individuals. When reconstructing brain responses to visual stimuli that differed by angular position, we found reliable localization to the appropriate retinotopic visual field quadrant by a minimum norm approach and by beamforming. Retinotopic map eccentricity in accordance with the fMRI map could not consistently be localized using an annular stimulus with any reconstruction method, but confining eccentricity stimuli to one visual field quadrant resulted in significant improvement with the minimum norm. These results inform the application of source analysis approaches for future MEG studies of the visual system, and indicate some current limits on localization accuracy of MEG signals.
脑磁图（MEG）允许以高时间分辨率记录人类大脑活动的生理信号。然而，MEG 信号源的空间定位是一个不适定的问题，因为仅信号本身不能约束唯一的解，必须施加额外的先验假设。用于研究人类视觉系统的适当源重建方法应该将早期视觉活动的源定位在枕叶皮层的已知位置。我们使用对比的重建方法（最小范数、多个稀疏先验和波束形成器）对人类大脑中的视网膜定位 MEG 信号进行了定位，并将这些结果与同一组个体的 fMRI 获得的视觉视网膜图进行了比较。当重建对视觉刺激的大脑反应时，这些刺激在角度位置上存在差异，我们发现最小范数方法和波束形成器可以可靠地将其定位到适当的视网膜视觉场象限。使用任何重建方法，都无法一致地用环形刺激来定位与 fMRI 图一致的视网膜图偏心率，但将偏心率刺激限制在一个视野象限内，最小范数方法的定位精度会显著提高。这些结果为未来视觉系统的 MEG 研究中的源分析方法的应用提供了信息，并表明 MEG 信号的定位精度存在一些当前的限制。
