Workshop on Diffusion MRI with Hiromasa Takemura

Hiromasa Takemura is a tenure-track researcher in the Center for Information and Neural Networks (CiNet), NICT, Japan. Takemura’s research centers on studies of human visual white matter pathways, spanning topics from vision science, comparative neuroanatomy, functional neuroimaging and clinical vision.

Takemura graduated from the University of Tokyo in 2007 with a B.A. in liberal arts. During his Ph.D. at the University of Tokyo, he worked on the psychophysical study of human visual motion perception. From 2012 to 2015, he carried out a series of studies on human visual white matter pathways as a postdoctoral fellow in the Wandell Laboratory at Stanford University. He joined CiNet, NICT in Japan in 2015.

TUTORIAL TALK – 2 pm

White Matter Imaging in Human Neuroscience: Diffusion MRI and Its Applications

In classical studies, neuroanatomists have identified that white matter in the human cerebral cortex is principally composed of bundles of axons (called tracts) and have emphasized the importance of long- range, white matter tracts in the understanding of cognitive functions. Recent advances in diffusion MRI (dMRI) and tractography provides us the opportunity to learn more about white matter tracts in living human brains, and, thus, to better understand how the white matter properties are related to development, disease, learning, and psychological measurements.

In this talk, I will first introduce an overview on the methodologies of acquiring dMRI data. Second, I will discuss several types of methods for modeling dMRI signals in a single voxel from a simpler diffusion tensor model up to complex multi-compartment models. Third, I will introduce advances in modeling white matter tracts (tractography) from deterministic tractography to recent global methods. I will further discuss advantages and limitations of dMRI as a method in systems neuroscience or psychology. The primary target audience is researchers with an interest in using dMRI for human studies. For each topic, background will be provided for audiences without detailed knowledge of specific methods or models. The goal of the tutorial is to provide an overview of what we can and cannot do with dMRI and help audience to consider how it may be useful for their research projects.

SCIENCE TALK – 3 pm

Multi-Dimensional Approaches to Understand the Visual White Matter Pathways

Over the past several decades, vision scientists have made great progress toward the functional organization of the cortical visual system, by identifying numerous brain areas that are specialized into different aspects of visual processing. However, one question remains largely unaddressed: how brain function emerges from either anatomical structures or from anatomical connections across discrete brain areas. Recent progress in diffusion MRI (dMRI) and tractography opens new avenues in understanding the relationship between ana– tomical connections and human visual or cognitive functions. This talk will highlight recent progress in elucidating the relationship between the properties of white matter tracts and visual function by combining dMRI with clinical, behavioral, functional or anatomical measurements.

I will first describe dMRI studies used to identify white matter pathways, such as the vertical occipital fascicles or the stratum proprium of interparietal sulcus, which have been reported in classical anatomical work but have been largely neglected in the literature. I will demonstrate that we can identify these tracts in living humans using dMRI and tractography methods and show that the trajectories of these tracts are consistent with invasive anatomical work performed in non-human primates. Using functional MRI, I will also discuss possible functions of these tracts. I will then describe my recent approaches for interpreting the tissue properties of visual white matter pathways in order to understand retinal disease and human visual performance by comparing dMRI-based measurements with clinical or psychophysical measurements. Finally, I will discuss some controversies concerning visual white matter pathways and how the analysis of ultra-high resolution polarized light imaging (Axer et al., 2011) data will help us to disentangle existing debates and further improve our understanding of visual white matter pathways.