Unraveling the mesoscopic functional organization of the human visual cortex using high-field MRI

哺乳动物皮层的一致性导致了这样一个命题，即存在基本的皮层操作单位，由几百或几千个在皮层区域内和跨皮层区域重复的神经元组成（Lorente de No '，1938）。新皮质的皮质柱和皮质层是这种结构和功能特化单位的突出例子。这些精细尺度的解剖结构出现在整个皮质区域。基于大量的动物实验，神经元的功能特性在同一列中是相似的，但在不同列之间是不同的。因此，可以说，研究大脑功能和行为之间关系的最佳空间尺度是皮质柱（和层，出于类似的原因）。这些精细尺度结构对视觉刺激的反应以及它们的自发活动现在可以在人脑中通过结合超高（7特斯拉或更高）磁场下的高分辨率功能性MRI（fMRI）和专门为此任务定制的分析方法来探测。 我的研究计划的长期目标是解开功能组织，功能，以及在人类大脑皮层的较低视觉区域的皮质柱和层的相互作用，以了解它们在支持感知中的机械作用。我们的第一个目标是开发一种新的方法来检测和纠正小的头部运动在高分辨率的fMRI时间序列的一个小的大脑体积。在我们的第二个目标中，我们将比较脑血容量为基础的功能磁共振成像和梯度和自旋回波（GRASE）血氧水平依赖（BOLD）功能磁共振成像在人类视觉皮层的空间特异性。我们的第三个目标是计算基于脑血容量的fMRI和GRASE BOLD fMRI在人类视觉皮层的空间点扩散函数。我们的第四个和第五个目标是同时图像，并定量表征和建模的完整地图的眼优势列和方向列，分别从整个初级视觉领域的人类受试者。 为了实现这些目标，我们将使用蒙特利尔神经学研究所和麦吉尔大学脑成像中心最近安装的西门子7特斯拉Terra扫描仪对人类受试者进行成像。我们将应用基于模型的分析以及数据驱动的机器学习技术。 我们期望，从解决目标1-3的发现将显着提高高分辨率的功能磁共振成像在皮层列和层的规模。它们可以为使用功能磁共振成像和解码技术发现精细皮层地图尚未显示的大脑区域中的精细功能组织提供基础，例如高阶关联区域。解决目标4-5的结果将为在皮层柱尺度上研究人类形状感知、立体视觉和双眼竞争的神经机制奠定基础。

The uniformity of the mammalian cortex has led to the proposition that there exist elementary cortical units of operation, consisting of several hundred or thousand neurons that are repeated within and across cortical areas (Lorente de No', 1938). Cortical columns and layers of the neocortex are prominent examples of such structurally and functionally specialized units. These fine-scale anatomical constructs appear throughout cortical areas. Based on numerous animal experiments, the functional properties are similar for neurons within a column but are known to vary between columns. It can, therefore, be argued that the optimal spatial scale for studying the relationship between brain function and behavior is that of cortical columns (and layers, for similar reasons). The responses of these fine-scale structures to visual stimuli as well as their spontaneous activity can now be probed in the human brain by combining high-resolution functional MRI (fMRI) at ultra-high (7 Tesla or higher) magnetic field and analysis methods specifically tailored for this task. The long term goal of my research program is to unravel the functional organization, the function, and the interactions of cortical columns and layers in lower visual areas of the human cerebral cortex, in order to understand their mechanistic roles in support of perception. Our first objective is to develop a novel method for detecting and correcting small head movements in high-resolution fMRI time-series of a small brain volume. In our second objective, we will compare the spatial specificity of cerebral blood volume-based fMRI and Gradient and Spin-Echo (GRASE) blood oxygenation level-dependent (BOLD) fMRI in the human visual cortex. Our third objective is to compute the spatial point-spread function of cerebral blood volume-based fMRI and GRASE BOLD fMRI in the human visual cortex. Our fourth and fifth objectives are to simultaneously image, and quantitatively characterize and model the complete maps of ocular dominance columns and orientation columns, respectively, from the entire primary visual area of human subjects. To realize these objectives, we will image human subjects using the recently installed Siemens 7 Tesla Terra scanner of the Brain Imaging Centre of the Montreal Neurological Institute and McGill University. We will apply model-based analysis as well as data-driven machine learning techniques. We expect that the findings from addressing objectives 1-3 will significantly improve high-resolution fMRI at the scale of cortical columns and layers. They can provide the basis for using fMRI and decoding techniques for discovering fine-scale functional organizations in regions of the brain where fine cortical maps have not been revealed, such as higher-order association areas. The results of addressing aims 4-5 will set the stage for investigating the neuronal mechanisms of human perception of shape, stereopsis and binocular rivalry at the scale of cortical columns.