Axon Tracts Within white matter, there are three different kinds of tracts or bundles of axons that connect one part of the brain to another and to the spinal cord: Projection tracts extend vertically between higher and lower brain and spinal cord centers. They carry information between the cerebrum and the rest of the body.
The corticospinal tracts, for example, carry motor signals from the cerebrum to the brainstem and spinal cord. Commissural tracts cross from one cerebral hemisphere to the other through bridges called commissures.
Commissural tracts enable the left and right sides of the cerebrum to communicate with each other. Association tracts connect different regions within the same hemisphere of the brain.
Among their roles, association tracts link perceptual and memory centers of the brain. White Matter-Grey Matter Interactions White matter forms the bulk of the deep parts of the brain and the superficial parts of the spinal cord.
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Krasnow, A. The frontal lobes are important for planning, reasoning, and judgment. As more scientific interest has been lavished on white matter, it has become clear that it is far from being a passive chunk of cabling; it is dynamic — its volume grows and shrinks with experience, it processes information — not just mindlessly passing data between points.
Certain conditions have long been associated with damage to the myelin sheath. White matter has even been implicated in stuttering and tone deafness. One of the most studied psychiatric conditions in relation to white matter is schizophrenia. One study that investigated 6, genes in the prefrontal cortex of schizophrenic brains provided damning evidence: of the 89 genes found to be abnormally regulated, 35 were involved in myelination.
Other studies have investigated white matter post-mortem, with some demonstrating abnormalities in white matter tracts and decreased numbers of oligodendrocytes in some regions of the brain. In fact, more recently, it has been shown that white matter tracts across the majority of the brain are disrupted in schizophrenia.
Schizophrenia tends to develop during adolescence, a time when the forebrain is finally being given its myelin coating. Some scientists believe that this might be more than a coincidence. Whether these changes are the cause of the condition or a consequence of the abnormal brain function is yet to be understood, but it is probably an intertwined two-way path.
Evidence of this came in a paper published in by Dr. Gabriel Corfas. He showed that disrupting the genetic control of oligodendrocytes could produce striking behavioral changes similar to those seen in schizophrenia. An imaging procedure called diffusion tensor imaging DTI , which is based on MRI technology, charts the relative movement of water within tissues. It can be used to observe white matter. DTI is based on the premise that, in normal brain tissue, water is equally likely to travel in any direction.
However, in tracts that are oriented in parallel and covered in myelin, it is more likely to move along them, rather than side to side. With this technology, the microstructure of white matter can be viewed; more tightly packed fibers with thicker myelin coats give stronger DTI signals.
This relatively new technology has been used to look for links between white matter and cognitive outcomes. Researchers have also demonstrated that using our brains in a specific way can change the structure of white matter.
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