machine brains

Michael Edelman mje at mich.com
Mon Mar 8 14:08:01 EST 1999



Malcolm McMahon wrote:

> >> But it _is_ pretty clear what constitutes wiring and what constitute
> >> transient electrical states in that wiring.
> >
> >But that still doesn't tell us what's program and what's data.
>
> Indeed, as a programmer I don't believe that there is any firm
> distinction. Data is more volatile. That's about it.

Unless you ROM the code, even that is up for debate.

> > Changes in wiring may be
> >actual axonal growth, or it may be long-term potentiation of synapses. And axonal growth
> >may be repair, not memory change.
>
> True, and dendritic growth is another aspect. In fact the latest news is
> that new neurons actually grow in mature rats' brains contrary to
> previous orthodoxy. But I don't have much doubt that a lot of these
> changes are related to learning.

But since "learning" can mean any change in the representational structure of the brain, that
may not buy you anything. There's a lot of integration of memory that takes place during REM
sleep, and if that resulted in structural change would you call that learning?

> I suspect there's something ressembling an evolutionary process going on
> in the CNS with neurons, dendrites, axions and synapses all forming more
> of less at random all the time and then dying back if they fail to
> justify their existance.

That would be very energy inefficient. Neurons don't grow at random. There needs to be some sort
of activity or chemical trigger.

> >ECT typically affects LTM as well, and I don't think it's accurate to say it "completely
> >scrambles the electrical state of the brain". It doesn't scramble it at all- rather, it
> >synchronizes it, much as occurs in a seizure- which is where the idea for ECT came from.
>
> I think it's probably pretty much like when your PC locks up and you
> switch it off for long enough for the capaciters to discharge, then
> start it up again.

Mm. Not quite.

In a seizure, you get a situtaiton where a pattern begins in one area and radiates outward from
that area, with the activation spreading outwards until a large portion of the neurons are
firing in syncrhonization. This goes on until limited by depletion of neurotransmitters, lack of
oxygen or some other limiting activity.

ECT sort of mimics this by firing a short jolt of AC accross the brain.

> Of course it's also known to do some actual brain damage so it's not
> surprising than LTM is somewhat affected.
>
> >The point still holds that we cannot distinguish structure from content, or program from
> >storage, in the brain; is a particular "wiring" the matrix on which a memory can be stored,
> >or is it the memory itself?
>
> That's what I'm saying.
>
> >> But our only awareness of consciousness is inherently subjective. We
> >> can't perceive consciousness, only experience it.
> >
> >There's that tricky "we" again. The point is that we all do experience conciousness. To
> >call it epiuphenomenal as some do is to define away an essential characterisitic of the
> >brain.
>
> I certainly don't dismiss its existance, only that it can be observed
> other than subjectively.

 So the quesiton is whether we can do science on conciousness. I think we can. We do a lot of
experiments that are subjective or objective depending on your philisophical orientation.
Someone last week wrote about an experiment he did comparing reaction times between taboo words
and  affect-neutral words. A behaviorist would look at it as factors influencing the S-R bond.
I'd look at it as an interaction between frequency effects in the organization of  the mental
lexicon and interference from concious processes mediating response.

--
Michael Edelman     http://www.mich.com/~mje





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