g., Gluhbegovic, 1980) provided a few key insights about the relatively coherent trajectories of macroscopic
fiber bundles within deep white Selleckchem Palbociclib matter. However, most of what is currently known about long-distance pathways in the human brain derive from two complementary neuroimaging approaches: analyses of “structural connectivity” based on diffusion imaging (dMRI) and analyses of “functional connectivity” (fcMRI) based on resting-state fMRI (rfMRI) scans. Both approaches emerged in the 1990s and have subsequently been improved dramatically, which is greatly enhancing our understanding of human brain circuits. However, the methods also remain indirect and subject to substantial limitations that are inadequately recognized. Here, the MDV3100 datasheet focus is on results from recent efforts by the HCP to improve the acquisition and analysis of structural and functional connectivity data and to enable comparisons with other modalities, including maps of function based on task-fMRI and maps of architecture (e.g., myelin maps) in individuals and group averages. One of the most important advances has been the use of improved scanning protocols, especially “multiband” pulse sequences that acquire data many slices at a time, thereby enabling better spatial and temporal resolution (Uğurbil et al.,
2013). Diffusion MRI (dMRI) relies on the preferential diffusion of water along the length of axons in order to estimate fiber bundle orientations in each voxel. This includes not only the primary (dominant) fiber bundle, but also the secondary and even tertiary fiber orientations that can be detected in many voxels. The HCP has achieved improved dMRI data acquisition by refining the pulse sequences, using a customized 3 Tesla scanner (with a more powerful “gradient insert”), and scanning each participant for a full hour (Sotiropoulos et al., 2013 and Uğurbil et al., 2013). This yields excellent data quality Chlormezanone with high spatial resolution: 1.25 mm
voxels instead of the conventional 2 mm voxels. Data preprocessing and analysis (distortion correction, fiber orientation modeling, and probabilistic tractography) have been improved, as has the capability for visualizing the results of tractography analyses. As an example, Figure 4 illustrates state-of-the-art analysis and visualization of the probabilistic fiber trajectories, starting from a seed point on the inferior temporal gyrus (Figure 4A) and viewed in a coronal slice (Figure 4B) and as a 3D trajectory through the volume (Figure 4C). Obviously, a major strength of tractography is that it provides evidence for the 3D probabilistic trajectories within the white matter. Information about the trajectories of major tracts is of interest for a variety of reasons.