why study neurology?

Brian zhil at online.no
Tue Jan 15 19:52:49 EST 2002


"mat" <mats_trash at hotmail.com> skrev i melding
news:43525ce3.0201151436.57e69ae1 at posting.google.com...
> > Well, why call it plasticity, wouldn't it be far better to term it "synaptic
efficiency"
> > or "synaptic enhancement" ?
> > Plasticity is centered on the mold, to form something new out of something
unfinished.
>
> The powers that be deemed it to be called plasticity.  There's nothing
> wrong with the term and in a functional sense it is plasticity - the
> temporal modulation of the efficency of the synapse.  As long as you
> are explicit about what type of thing you're talking about its ok.

Ok, got it.

> Long/Short term potentiation/depression (STP, STD, LTP, LTD) are the
> terms usually used to describe changes in synaptic efficency.
> Plasticity is a word for the general phenomenon of synaptic change.
> Over the past year there have been some really good articles in Neuron
> and Nature Neuroscience concerning how spike coincidences effect
> changes in synpatic strength.

This doesn't seem strange at all, in short wouldn't it be "use it or loose it" ?
Well, I have enough with 'Principles' for the foreseeable future, but thanks for the
tip.

> > Synapses are not very changeable, but their efficiency, effectiveness or enhancement
> > could be improved.
>
> yep.  But I thought you said you were looking into the 'not very
> changeable' aspects?

Yes, as in growing new axons -> synaptic connections to form new memories.
That is just one aspect that seemed interesting.
This was in connection with the article that Yan posted.

> Depending on how you view the way brain function
> arises from its structure then the change in synaptic efficency may be
> the most important form of plasticity (for instance in computational
> theories)  Changing the spatial distribution of synapses seems
> intuitively to be too slow a mechanism to account for the
> computational aspects of brain function.  Depression and potentiation
> of synapses can occur over seconds and smaller timescales.

Dr.Calvin described one way were structures 'compete' with each other to gain attention;
that is - they try to increase their dominance over a larger 'tract' of the neocortex
(he was particularly interested in the pyramidal cells, I think it was in layer I-III).
Each cell was connected with several other cells, and each _unique_ structure could call
forth _one_ aspect of the same memory.
And this competition would have to be fast, to grab our attention either from excited
memories, or from external sources through the Thalamus.
Thus the need for the timescale in milliseconds up to seconds and minutes.

> > > Cells exhibiting plasticity of the form you describe were recently
> > > photographed doing so in a paper in the journal Cell, probably worth a
> > > look (Principles of Neural Science is only an intro!).
> >
> > Ahhh, now this looks interesting.
>
> It was, they were grown on a silicon wafer and selectively stimulated.
>  The synapses were videoed changing.

Really ?
I never thought they would grow them on silicon.................the petri-dish was what
I thought were the 'trade'-mark of neuroscience, well - in every biological field anyway
:)

> > Anyway, Yan did a report on this during REM-sleep.
>
> Really? Synaptic plasticity in vivo?  A study demonstrating the growth
> of new synapses during sleep?  If thats true then that would be a
> remarkable paper.  The reason that the Cell paper I mentioned was so
> important is that though it has always been a prediction, seeing
> synapses do their thing has never been accomplished until now

I hope I didn't get you to excited, you have to ask him for the article.
His email is y.k.y at lycos.com - and tell that I was refering to the article.
I lost the article due to a harddisk crash.........
Well, it is at least one advantage with books.

> > > But again I
> > > would be weary of the direct associations you make.  It is by no means
> > > certain that the cognitive functions into which we have divided our
> > > minds map isomorphically to singular neural processes, in fact I would
> > > tentatively suggest that it is highly unlikely.
> >
> > Thanks for your input.
> > I was thinking along Dr.Calvin's idea of Darwin machines, and was thinking how this
> > could fit in biologically.
> > He described it in "The Celebral Code".
>
> Though the cerebral code is undoubtably an interesting idea, and I
> know that Calvin makes it reasonably explicit that we shouldn't expect
> to actually see hexagons pattening the cortex his theory is a bit
> questionable.  One of the main premises is this idea that pyramidal
> cortical neurones in layer 4 consistently synapse on to similar cells
> approximately 0.5mm away.  I've seen quite a lot of evidence to
> suggest that holding this to be true over the whole cortex is a gross
> generalisation and highly simplistic.  However, perhaps the most
> valuable thing that Calvin contributes is not the theory itself but
> demonstrating how we might go about constructing one based on more
> sound (and inherently more complex) neurobiological principles.

I found the theory quite interesting, and I'm quite glad that you know what I mean when
I refer to the Darwin-machine, hexagonal patterns etc.
It isn't that every brain is like, but that the overall general structure corresponds
between every person (Occipital lobe used to process visual cues, somatosensory cortex,
pre- and motor-cortex etc.).
And that the hexagonal pattern compete as an overlay, depending on the cues.
Of course visual cues might not be stored only in the occipital lobe, but being spread
over a large part of the neocortex (it would indeed seem very strange, if it didn't
require at least more space than the occipital lobe).

Brian





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