[ExI] all we are is just llms

[Ben Zaiboc]

On 25/04/2023 00:00, spike wrote:
>
> In any case, I don’t know what that spike-trains business is about.  
> Ben, do explain please. Sounds kinda cool.
>

Try: 
http://www.neuwritewest.org/blog/2015/1/3/ask-a-neuroscientist-whats-a-spike-train

Gives some information, but doesn't explain how they arise, and why they 
are digital signals.

Not to get too technical, neurons 'fire' by depolarising the cell 
membrane. This means that the normal distribution of electrical charge 
across the membrane is reversed. This is all to do with ions of various 
types and ion channels (proteins that span the membrane and allow 
specific ions through) and pumps (that actively pump certain ions 
through the membrane).

In total, the membrane is like a capacitor that tends to settle at a 
certain voltage. Certain events can make the membrane quickly 
'discharge', reversing polarity, to a second specific voltage. I forget 
the exact numbers now, but they're easily found by searchiong the web 
(or asking an AI). A single depolarisation is a 'spike'. You could 
represent this like so: ________|_______

That's a section of neuronal membrane at resting potential being 
depolarised to a specific voltage then quickly resetting to normal. This 
happens very quickly, and the voltages are always the same. So, 
effectively, this is a digital signal: 000000000100000000.

Spike trains are clusters of these signals that travel down the axons 
(pipes that extend out from each neuron, carrying the signals away, to 
other neurons) and dendrites (similar pipes that bring signals to the 
neuron body).

The integration and general signal processing that the neuron does is 
complex and I don't understand it all, but can be thought of as 
something like a logic gate processing incoming digital signals and 
producing an output. Each neuron has many (thousands, usually) of 
incoming dendrites, and (usually) a single axon leading away to other 
neurons.

That might have been in more detail than you wanted or needed, but is 
still a very dumbed-down, 'without numbers' version (and the numbers are 
important to fully understand the process), and there are many 
variations on this, so if anyone knows neurphysiology, please don't be 
outraged at this version. You need to study this stuff in a lot more 
depth to get a proper idea of how it works.

Also, I am not an expert. This is my graduate-level-and-below 
understanding, and is probably out of date now. But the broad principle 
is sound.

One other thing I will say: biology is messy. These 'digital' signals 
are not nice and neat like bytes and words in a computer. Each 
individual spike is the same as all the others, but the 'trains' I keep 
mentioning are of different lengths, occur at different frequencies, and 
of course occur in millions of individual axons. This is why when people 
say "The brain is not a computer!!1!" I groan. It's just not that 
simple. The brain is like a computer in some ways, and not like one in 
others, is really all you can sensibly say.

Ben
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