School of Computing, Informatics, and Decision Systems Engineering, Arizona State University, Tempe, Arizona, United States of America.
Division of Arts and Sciences, New York University Shanghai, Shanghai, China.
PLoS Comput Biol. 2021 Aug 2;17(8):e1009216. doi: 10.1371/journal.pcbi.1009216. eCollection 2021 Aug.
Retinotopic mapping, i.e., the mapping between visual inputs on the retina and neuronal activations in cortical visual areas, is one of the central topics in visual neuroscience. For human observers, the mapping is obtained by analyzing functional magnetic resonance imaging (fMRI) signals of cortical responses to slowly moving visual stimuli on the retina. Although it is well known from neurophysiology that the mapping is topological (i.e., the topology of neighborhood connectivity is preserved) within each visual area, retinotopic maps derived from the state-of-the-art methods are often not topological because of the low signal-to-noise ratio and spatial resolution of fMRI. The violation of topological condition is most severe in cortical regions corresponding to the neighborhood of the fovea (e.g., < 1 degree eccentricity in the Human Connectome Project (HCP) dataset), significantly impeding accurate analysis of retinotopic maps. This study aims to directly model the topological condition and generate topology-preserving and smooth retinotopic maps. Specifically, we adopted the Beltrami coefficient, a metric of quasiconformal mapping, to define the topological condition, developed a mathematical model to quantify topological smoothing as a constrained optimization problem, and elaborated an efficient numerical method to solve the problem. The method was then applied to V1, V2, and V3 simultaneously in the HCP dataset. Experiments with both simulated and real retinotopy data demonstrated that the proposed method could generate topological and smooth retinotopic maps.
视域映射,即视网膜上的视觉输入与皮质视觉区域中神经元活动之间的映射,是视觉神经科学的核心主题之一。对于人类观察者,通过分析皮质对视网膜上缓慢移动的视觉刺激的功能磁共振成像 (fMRI) 信号来获得映射。尽管神经生理学已经很好地证明了在每个视觉区域内,映射是拓扑的(即,邻域连接的拓扑结构得以保留),但由于 fMRI 的信噪比和空间分辨率较低,从最先进的方法中得出的视域图通常不是拓扑的。拓扑条件的违反在对应于中央凹附近的皮质区域中最为严重(例如,在人类连接组计划(HCP)数据集中<1 度的偏心度),这极大地阻碍了对视域图的准确分析。本研究旨在直接模拟拓扑条件,并生成保持拓扑结构的平滑视域图。具体来说,我们采用了 Beltrami 系数,一种拟共形映射的度量,来定义拓扑条件,开发了一个数学模型,将拓扑平滑量化为一个受约束的优化问题,并详细阐述了一种有效的数值方法来解决这个问题。然后,该方法被应用于 HCP 数据集中的 V1、V2 和 V3 区域。使用模拟和真实视域数据的实验表明,所提出的方法可以生成具有拓扑结构和平滑的视域图。