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<div class="moz-cite-prefix">On 25/04/2023 00:00, spike wrote:<br>
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cite="mid:mailman.574.1682377224.847.extropy-chat@lists.extropy.org">
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<p class="MsoNormal">In any case, I don’t know what that
spike-trains business is about. Ben, do explain please.
Sounds kinda cool.</p>
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Try:
<a class="moz-txt-link-freetext" href="http://www.neuwritewest.org/blog/2015/1/3/ask-a-neuroscientist-whats-a-spike-train">http://www.neuwritewest.org/blog/2015/1/3/ask-a-neuroscientist-whats-a-spike-train</a><br>
<br>
Gives some information, but doesn't explain how they arise, and why
they are digital signals.<br>
<br>
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).<br>
<br>
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: ________|_______<br>
<br>
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.<br>
<br>
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).<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
Ben<br>
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