Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal.
Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
Hum Brain Mapp. 2018 Jun;39(6):2426-2441. doi: 10.1002/hbm.24012. Epub 2018 Feb 20.
External stimuli and tasks often elicit negative BOLD responses in various brain regions, and growing experimental evidence supports that these phenomena are functionally meaningful. In this work, the high sensitivity available at 7T was explored to map and characterize both positive (PBRs) and negative BOLD responses (NBRs) to visual checkerboard stimulation, occurring in various brain regions within and beyond the visual cortex. Recently-proposed accelerated fMRI techniques were employed for data acquisition, and procedures for exclusion of large draining vein contributions, together with ICA-assisted denoising, were included in the analysis to improve response estimation. Besides the visual cortex, significant PBRs were found in the lateral geniculate nucleus and superior colliculus, as well as the pre-central sulcus; in these regions, response durations increased monotonically with stimulus duration, in tight covariation with the visual PBR duration. Significant NBRs were found in the visual cortex, auditory cortex, default-mode network (DMN) and superior parietal lobule; NBR durations also tended to increase with stimulus duration, but were significantly less sustained than the visual PBR, especially for the DMN and superior parietal lobule. Responses in visual and auditory cortex were further studied for checkerboard contrast dependence, and their amplitudes were found to increase monotonically with contrast, linearly correlated with the visual PBR amplitude. Overall, these findings suggest the presence of dynamic neuronal interactions across multiple brain regions, sensitive to stimulus intensity and duration, and demonstrate the richness of information obtainable when jointly mapping positive and negative BOLD responses at a whole-brain scale, with ultra-high field fMRI.
外部刺激和任务经常会在大脑的不同区域引起负的 BOLD 反应，越来越多的实验证据支持这些现象具有功能意义。在这项工作中，利用 7T 的高灵敏度，探索了正（PBRs）和负 BOLD 反应（NBRs）的映射和特征，这些反应发生在视觉棋盘刺激的大脑的不同区域，包括视觉皮层内外的区域。最近提出的加速 fMRI 技术被用于数据采集，以及排除大引流静脉贡献的程序，加上 ICA 辅助去噪，被包括在分析中，以提高响应估计。除了视觉皮层，在外侧膝状体核和上丘，以及中央前回，也发现了显著的 PBR；在这些区域，响应持续时间随刺激持续时间单调增加，与视觉 PBR 持续时间紧密协变。在视觉皮层、听觉皮层、默认模式网络（DMN）和顶叶上回，发现了显著的 NBR；NBR 持续时间也倾向于随刺激持续时间增加，但与视觉 PBR 相比，持续时间明显较短，尤其是对于 DMN 和顶叶上回。进一步研究了棋盘对比度依赖性的视觉和听觉皮层的反应，发现它们的振幅随对比度单调增加，与视觉 PBR 振幅线性相关。总的来说，这些发现表明，在多个大脑区域之间存在动态的神经元相互作用，对刺激强度和持续时间敏感，并证明了在全脑尺度上联合绘制正和负的 BOLD 反应时，可以获得丰富的信息，这得益于超高场 fMRI。
