Change in the brain's white matter

There aren't many review articles on the cellular mechanisms through which changes in the brain's white matter can affect cognition, but this is the latest from R Douglas Fields who also wrote a review in 2005 entitled "Myelination: an overlooked mechanism of synaptic plasticity".  His reviews continue to be a wonderful resource for me because they cover not only the human cognitive experiments that are closest to my line of work, but also the animal behavioral and the cellular studies which are essential to the interpretation of MRI findings in living humans.

This article not only provides a beautiful picture of a couple of oligodendrocytes myelinating axons (below) which will probably be a great future figure for me, but also outlines the proposed mechanisms through which oligodendrocytes could know which axons are being taxed and how neuronal impulse activity could affect myelination.

Myelin that coats and insulates neuronal axons may control the propagation of electrical impulses in a manner that affects information processing.

The best new resource that this review has lead me to is this paper on myelination of the corpus callosum in male and female rats following complex environment housing during adulthood.  I'm really excited to read that paper (tomorrow?) and unpack their finding that:

Although the area of the splenium (posterior 20% of the callosum, which contains axons from visual cortical neurons) increased by about 10% following two months of EC [enriched] housing, the area occupied by myelinated axons was not influenced by adult housing condition. Instead, it was the area occupied by glial cell processes and unmyelinated axons which significantly increased following EC housing.

This means that after training, while myelination may increase (as has been suggested in human neuroimaging papers) there is also evidence for a relative decrease in myelin as astrocytes and unmyelinated axons take up more space.

Stay tuned, and thank you Dr Fields for another great review :)

Neuroscience. Change in the brain's white matter.

Fields RD.

Science. 2010 Nov 5;330(6005):768-9. No abstract available.
PMID: 21051624