[extropy-chat] A couple weird questions...

[Hal Finney]

Jeffrey Herrlich writes:
> Thanks for your response. At the beginning of the thread titled "Dead
> Time of the Brain" (a long, long time ago), I made a back-of-the-envelope
> calculation which seemed to show that there exists a significant delay
> between the firing/discharging of *any* two neurons in the brain,
> arbitrarily located *anywhere* in the brain, ranging from a 3 nm
> separation to 6 inch separation (- it doesn't matter). Here's a quick
> recap of the calculation:
>
>   1 Second / 1000 Firings / 100 Billion Neurons / 10^ -43 Seconds = ...
>
> ... Approximately 10^29 Planck Intervals during which not a single neuron
> anywhere could be firing within the human brain (based on its limited
> parameters). The "1000 Firings" above represents the high upper limit
> on the frequency of cycles/firings of the fastest of neurons within
> the brain.

That's probably not the right way to look at it.  Each neural firing
lasts a millisecond or more.  It's a somewhat complex process, involving
a cascade of ion channels opening, ions rushing in (or out), electrical
potentials varying, resulting in an explosive climax, not unlike a sneeze.

The bottom line is, from Anders' comment, that a typical neuron spends
maybe 2% of its time in the firing state.  With 100 billion neurons that
means that we have 2 billion neurons firing at any one time.

Plus even when a neuron is technically not firing, it is still
doing stuff.  It constantly senses its environment, particularly
the neurotransmitter concentration.  It may be subject to continual
small pulses of neurotransmitter that fail to raise its electrical
potential to the threshold necessary to trigger a firing (like when
you get that "almost" feeling when you don't quite sneeze).  From the
information-theory perspective, failing to fire sends information just
like firing does.  (Not as much information, since firing is less common
than not firing, but information nonetheless.)

Hal Finney