A Theory of Sleep

Brian zhil at online.no
Sat Aug 18 09:45:16 EST 2001


"yan king yin" <y.k.y@(no spam please)lycos.com> skrev i melding
news:9lkjot$om31 at imsp212.netvigator.com...
>
> "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.

Sounds like the brain is consolidating itself to me,making it more
efficient.
The the brain developes through apoptosis (programmed cell-death) from
birth, of
course depending of it's usage.
But the downside is of course the danger of reducing the numbers to much, to
make it more vulnerable and dependant on each cell.

> 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...

Hmm, that is longterm memory, but short-time memory goes through the
selective attention system (Thalamus) and then through Hippocampus.
I wonder if attention is directly connected to short-time memory, and that
somehow stimulates myelination......
But what perplexes me are those changes of levels in myelination you
mentioned.
Anyway, correct me if I'm mistaken - "Conversations vith Neils Brain" is
quite
good, but there are more to it I suspect.

> > 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 =)

As if it not comprehensible from before :)

Brian





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