Hemodynamic Traveling Waves in Human Visual Cortex

Functional MRI (fMRI) experiments rely on precise characterization of the blood oxygen level dependent (BOLD) signal. As the spatial resolution of fMRI reaches the sub-millimeter range, the need for quantitative modelling of spatiotemporal properties of this hemodynamic signal has become pressing. Here, we find that a detailed physiologically-based model of spatiotemporal BOLD responses predicts traveling waves with velocities and spatial ranges in empirically observable ranges. Two measurable parameters, related to physiology, characterize these waves: wave velocity and damping rate. To test these predictions, high-resolution fMRI data are acquired from subjects viewing discrete visual stimuli. Predictions and experiment show strong agreement, in particular confirming BOLD waves propagating for at least 5–10 mm across the cortical surface at speeds of 2–12 mm s-1. These observations enable fundamentally new approaches to fMRI analysis, crucial for fMRI data acquired at high spatial resolution.

功能磁共振成像（Functional MRI, fMRI）实验依赖于对血氧水平依赖（blood oxygen level dependent, BOLD）信号的精准表征。随着功能磁共振成像的空间分辨率达到亚毫米级，对该血液动力学信号的时空特性进行定量建模的需求日益迫切。本研究发现，针对血氧水平依赖响应的精细化生理学时空模型，可预测出波速与空间跨度均处于实验可观测范围内的行波。有两个与生理学相关的可测量参数可表征此类行波：波速与阻尼率。为验证上述预测，研究人员对接收离散视觉刺激的受试者采集了高分辨率功能磁共振成像数据。预测结果与实验数据高度吻合，尤其证实了血氧水平依赖信号行波可在大脑皮层表面传播至少5至10毫米，传播速度为2至12毫米每秒。上述观测结果为功能磁共振成像分析开辟了全新的研究路径，这对于高空间分辨率功能磁共振成像数据的处理至关重要。