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This shape is often modeled as an ellipsoid, and the technique is then called diffusion tensor imaging. [4] Barriers can be many things: cell membranes, axons, myelin, etc.; but in white matter the principal barrier is the myelin sheath of axons. Bundles of axons provide a barrier to perpendicular diffusion and a path for parallel diffusion ...
White matter is composed of bundles, which connect various grey matter areas (the locations of nerve cell bodies) of the brain to each other, and carry nerve impulses between neurons. Myelin acts as an insulator, which allows electrical signals to jump , rather than coursing through the axon, increasing the speed of transmission of all nerve ...
[48] [49] Researchers use statistical methods to construct a 3-D parametric map of the brain indicating the regions of the cortex that demonstrate a significant change in activity in response to the task. Compared to anatomical T1W imaging, the brain is scanned at lower spatial resolution but at a higher temporal resolution (typically once ...
The external capsule is a series of white matter fiber tracts in the brain. These fibers run between the most lateral (toward the side of the head) segment of the lentiform nucleus (more specifically the putamen) and the claustrum. The white matter of the external capsule contains fibers known as corticocortical association fibers.
Grey matter undergoes development and growth throughout childhood and adolescence. [3] Recent studies using cross-sectional neuroimaging have shown that by around the age of 8 the volume of grey matter begins to decrease. [4] However, the density of grey matter appears to increase as a child develops into early adulthood. [4]
This allows researchers to quantify anatomical features of the brain in terms of shape, mass, volume (e.g. of the hippocampus, or of the primary versus secondary visual cortex), and to derive more specific information, such as the encephalization quotient, grey matter density and white matter connectivity, gyrification, cortical thickness, or ...
For example, deep white matter hyperintensities are 2.5 to 3 times more likely to occur in bipolar disorder and major depressive disorder than control subjects. [3] [4] WMH volume, calculated as a potential diagnostic measure, has been shown to correlate to certain cognitive factors. [5]
The VBM analysis showed global gray matter was decreased linearly with age, especially for men, whereas global white matter did not decline with age. A key description of the methodology of voxel-based morphometry is Voxel-Based Morphometry—The Methods [ 9 ] —one of the most cited articles in the journal NeuroImage . [ 10 ]