Department of Psychological and Brain Sciences, Dartmouth College, NH 03755, USA.
Neuroimage. 2013 Sep;78:249-60. doi: 10.1016/j.neuroimage.2013.04.019. Epub 2013 Apr 13.
How quickly can information about the neural response to a visual stimulus be detected in the hemodynamic response measured using fMRI? Multi-voxel pattern analysis (MVPA) uses pattern classification to detect subtle stimulus-specific information from patterns of responses among voxels, including information that cannot be detected in the average response across a given brain region. Here we use MVPA in combination with rapid temporal sampling of the fMRI signal to investigate the temporal evolution of classification accuracy and its relationship to the average regional hemodynamic response. In primary visual cortex (V1) stimulus information can be detected in the pattern of voxel responses more than a second before the average hemodynamic response of V1 deviates from baseline, and classification accuracy peaks before the peak of the average hemodynamic response. Both of these effects are restricted to early visual cortex, with higher level areas showing no difference or, in some cases, the opposite temporal relationship. These results have methodological implications for fMRI studies using MVPA because they demonstrate that information can be decoded from hemodynamic activity more quickly than previously assumed.
使用 fMRI 测量血流动力学反应时，能多快检测到对视觉刺激的神经反应的信息？多体素模式分析（MVPA）使用模式分类来检测体素反应模式中的细微刺激特异性信息，包括无法从给定脑区的平均反应中检测到的信息。在这里，我们结合 fMRI 信号的快速时间采样，研究分类准确性的时间演变及其与平均区域血流动力学反应的关系。在初级视觉皮层（V1）中，在 V1 的平均血流动力学反应偏离基线之前超过一秒钟，就可以在体素反应模式中检测到刺激信息，并且分类准确性在平均血流动力学反应的峰值之前达到峰值。这两种效应都仅限于早期视觉皮层，而高级区域则没有差异，或者在某些情况下，呈现相反的时间关系。这些结果对使用 MVPA 的 fMRI 研究具有方法学意义，因为它们表明可以比以前假设的更快地从血液动力学活动中解码信息。
