RE: where do copies come from?

From: Brent Meeker <meekerdb.domain.name.hidden>
Date: Mon, 11 Jul 2005 13:11:29 -0000

>-----Original Message-----
>From: Stathis Papaioannou [mailto:stathispapaioannou.domain.name.hidden]
>Sent: Friday, July 08, 2005 6:33 AM
>To: meekerdb.domain.name.hidden
>Cc: everything-list.domain.name.hidden
>Subject: RE: where do copies come from?
>
>
>>Brent Meeker writes:
>
>>I find it hard to believe that something as stable as memories that last
>>for
>>decades is encoded in a way dependent on ionic gradients across cell
>>membranes
>>and the type, number, distribution and conformation of receptor and ion
>>channel
>>proteins. What evidence is there for this? It seems much more likely that
>>long term memory would be stored as configuration of neuronal connections.
>
>You have to keep in mind that every living organism is being continually
>remodelled by cellular repair mechanisms. Jesse Mazer recently quoted an
>article which cited radiolabelling studies demonstrating that the entire
>brain is turned over every couple of months, and the synapses in particular
>are turned over in a matter of minutes. The appearance of "permanent"
>anatomical structures is an illusion due to the constant expenditure of
>energy rebuilding that which is constantly falling apart.

So? I don't see the point of this observation. If the structure is
maintained, then the structure *is* permanent and is suitable for storing long
term memories. The fact that the physical elements of the structure are
replaced every five seconds or every ten years is neither here or nor there.

>If anything,
>parameters such as ionic gradients and protein conformation are more closely
>regulated over time than gross anatomy.

Gradients where? Surely you aren't saying that there is a pattern of gradients
in the brain that is relative to (x,y,z) coordinates and is independent of the
neuronal structures.

>Cancer cells may forget who they
>are, what their job is, what they look like and where they live, but if an
>important enzyme curled up a little tighter than usual due to corruption of
>intracellular homeostasis mechanisms, the cell would instantly die.

I doubt that any memories are stored in intracelluar chemistry.

>
>Recent theory based on the work of Eric Kandel is that long term memory is
>mediated by new protein synthesis in synapses, which modulates the
>responsiveness of the synapse to neurotransmitter release; that is, it isn't
>just the "wiring diagram" that characterises a memory, but also the unique
>properties of each individual "connection".

I would not have supposed otherwise. I would guess that memories are stored as
they are in artificial neural networks: in the wiring diagram PLUS the strength
of the connections.

>But let's suppose, for the sake
>of argument, that each distinct mental state were encoded by the simplest
>possible mechanism: the "on" or "off" state of each individual neuron. This
>would allow 2^10^11 possible different mental states - more than enough for
>trillions of humans to live trillions of lifetimes and never repeat a
>thought.

Yes, I'm well aware that a brain is really really complicated.

>In theory, it should be possible to scan a brain in vivo using some
>near-future MRI analogue and determine the state of each of the 10^11
>neurons, and store the information as a binary srtring on a hard disk. Once
>we had this data, what would we do with it? The details of ionic gradients,
>type, number and conformation of cellular proteins,

But what is the evidence that these play are part in long term memory?

>anatomy and type of
>synaptic connections,

That's wiring diagram and strength of connections.

>etc. etc. etc., would be needed for each neuron, along
>with an accurate model of how they all worked and interacted, in order to
>calculate the next state, and the state after that, and so on.

But calculating the next state corresponds to continuing consciousness without
a gap. That I agree would require simulating all the gradients, etc, down to
near molecular level. But my original contention was that you could simulate a
person, with a memory gap such as incurred under anesthesia, by just the wiring
diagram plus strength of connnections.

>This would be
>difficult enough to do if each neuron were considered in isolation, but in
>fact, there may be hundreds of synaptic connections between neurons, and the
>activity of each connected neuron needs to be taken into account, along with
>the activity of each of the hundreds of neurons connected to each of *those*
>neurons, and so on.

Sure - but that's still wiring diagram. I didn't say it was simple; but it's
a lot simpler than trying to capture the instantaneous chemistry.

Brent Meeker
Received on Mon Jul 11 2005 - 17:07:37 PDT