<P> Changes in white matter known as amyloid plaques are associated with Alzheimer's disease and other neurodegenerative diseases . White matter injuries ("axonal shearing") may be reversible, while gray matter regeneration is less likely . Other changes that commonly occur with age include the development of leukoaraiosis, which is a rarefaction of the white matter that can be caused by a variety of conditions, including loss of myelin, axonal loss, and a breakdown of the blood--brain barrier . </P> <P> The study of white matter has been advanced with the neuroimaging technique called diffusion tensor imaging where magnetic resonance imaging (MRI) brain scanners are used . As of 2007, more than 700 publications have been published on the subject . </P> <P> A 2009 paper by Jan Scholz and colleagues used diffusion tensor imaging (DTI) to demonstrate changes in white matter volume as a result of learning a new motor task (e.g. juggling). The study is important as the first paper to correlate motor learning with white matter changes . Previously, many researchers had considered this type of learning to be exclusively mediated by dendrites, which are not present in white matter . The authors suggest that electrical activity in axons may regulate myelination in axons . Or, gross changes in the diameter or packing density of the axon might cause the change . A more recent DTI study by Sampaio - Baptista and colleagues reported changes in white matter with motor learning along with increases in myelination . </P>

Where is the white matter located in the brain