Introducing the brain: myelin more than insulation (Introduction)

by David Turell , Friday, November 12, 2021, 14:56 (893 days ago) @ David Turell

It is active in brain plasticity:

https://www.sciencemagazinedigital.org/sciencemagazine/12_november_2021/MobilePagedArti...

"The brain is responsive to an ever-changing environment, enabling the organism to learn and change behavior accordingly. Efforts to understand the underpinnings of this plasticity have almost exclusively focused on the functional and underlying structural changes that neurons undergo at neurochemical synapses. What has received comparatively little attention is the involvement of activity-dependent myelination in such plasticity and the functional output of circuits controlling behavior. The traditionally held view of myelin as a passive insulator of axons is changing to one of lifelong changes in myelin, modulated by neuronal activity and experience. We review the nascent evidence of the functional role of myelin plasticity in strengthening circuit functions that underlie learning and behavior.

"More than half of the human brain is white matter, which supports rapid and synchronized transfer of information across the many gray-matter areas of the central nervous system (CNS). The function of white matter depends on oligodendrocytes. These specialized glial cells wrap a lipid-rich membrane, myelin, around axons in the CNS, increasing the speed of the action potential and providing axons with energy for impulse propagation required for maintaining high impulse frequency.Changes inmyelinwithin a tract or brain region can affect the function of neural circuits, such as those involved in emotion, cognition, motivation, and associated behavior, by fine-tuning and reducing the failure rate of information transfer between different areas in the brain's gray matter.

"Although the essential function of myelin has long been recognized in white-matter diseases such as multiple sclerosis, where myelin loss leads to both motor and cognitive dysfunction, it remains widely viewed as a passive insulator. However, evidence indicates that myelination in mammals is a protracted dynamic process involved in CNS function and development. Myelination in humans begins during the last trimester and extends into late adulthood and varies between individuals, potentially affecting personality traits.

"Human postmortem histological observations suggest that myelination of axonal tracts linking brain regions is synchronized with the functional maturation of the neural circuits they form. Likewise, magnetic resonance imaging (MRI) studies have revealed that the maturation of sensorimotor or language-related white-matter tracts in humans is associated with the development of these basic skills in childhood, whereas the maturation of frontoparietal and frontostriatal white-matter pathways coincides with protracted development of executive functions and behavioral control during adolescence and early adulthood.

"Evidence is accumulating that myelination is not confined to the developmental period; rather, it now appears that myelin turns over and its patterns change throughout the lifespan, which may relate to experience-dependent changes in the function of neural circuits. Here, we focus on the functional implications of myelin changes, capitalizing on previous reviews of mechanisms of myelin plasticity to assess how these might be linked to circuit function underlying learning and memory.

Comment: extremely long review article of current preliminary research. Here we see major new complexity discovered in the plasticizing processes of the brain. These processes must be designed all at once to be useful. Only design can do this, not chance mutations.