A Theory of Sleep

yan king yin (no spam please) y.k.y at lycos.com
Fri Aug 17 21:37:24 EST 2001

"Brian" <zhil at online.no>:

> "yan king yin":
> > Some neurites undergo maturation in the cytoskeleton and also myelination.
> > After that their structure is much more stabilized, and it seems that this
> > process is irreversible. Maybe the brain is modular so that some neurons
> > retain plasticity while others are more stable.
> Thanks for the reply.
> Your last point about plasticity of the neurites, question - are there any
> papers about which neurites remain the plasticity and those that stabilize ?

I dont know what causes some axons to be myelinated and others not.
A study by Francine Benes says:

"Myelination levels kept rising into the early twenties, she found, and then
flattened out after having doubled in the second decade of life. But myelination
took off again in the forties and continued into the mid fifties, accumulating, on
average, another increase of 50 percent before leveling off again."

I dont know what to make of it.. it doesnt correlate very well with
learning and cognitive abilities.

Also I found this review in PubMed:

Neurol Neurochir Pol 2000;34(3 Suppl):41-4 Related Articles, Books
[Pivotal role of axonal adhesion molecules in central nervous system myelination].
[Article in Polish] Lubetzki C, Charles P, Stankoff B, Hernandez P, Zalc B.

In the abstract it says that "blocking or stimulating electrical activity may
inhibit or induce myelination respectively".

I speculated that some neurons might retain plasticity because different
neurotransmitter receptor subtypes are expressed in different regions of
the brain, and the hippocampus is more strongly associated with various
forms of amnesia (eg failure to form new memories) than other brain
regions, and its lesion does not cause loss of early memory. This is cited
as evidence that the hippocampus consolidates memory but does not
store it. But according to the selectionist perspective, memory should be
distributed in all brain regions. This is very perplexing...

> By the way, I logged onto your homepage and there was a picture of a male,
> was that you ?  (He seemed to say "Hey you!")

It was me last summer visiting London, i'll update it soon =)

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