[extropy-chat] Desirability of Singularity (was Are ancestor simulations immoral?)
mstriz at gmail.com
Mon Jun 5 20:03:00 UTC 2006
On 6/4/06, Anders Sandberg <asa at nada.kth.se> wrote:
> > And I would expect much more than a thousand ions released per
> > total synaptic spike.
> Surprisingly enough, it is on the order of 100,000 ions. Much more than a
> thousand, but still far far from moles.
Is that really surprising? Typical extra/intracellular chemical
concentrations are in the nanomolar range, and only a tiny fraction of
that would be involved in the reaction along the axonal membrane. The
MW of sodium is 23. Would you expect 23 grams of sodium to be
involved in a single spike event?
> > So the inefficiency relative to the thermodynamic
> > limit is surely more than just three orders of magnitude.
> The Brillouin inequality is only about information erasure. Many of the
> brain computations may be rather information-preserving. A synaptic signal
> for example, if perfect, would not cost any thermodynamic cost for
> erasure. In practice the release probability is 10-30% according to
> Markram and Tsodyks ( http://diwww.epfl.ch/~gerstner/SPNM/node33.html ),
> so that would be on average 2-3 bits of erasure per synapse and signal.
> Hmm, around 8e14 synapses with an average population of 1-10% neurons
> firing at 1-100 Hz. That makes 1e9-1e12 firings affecting 8e12-8e15
> synapses. At a cost of 2.4e-21 - 3.6e-21 J
What is the conversion you're using (i.e. J/spike)? How do you derive
it? Are you taking the total energy demands of a neuron over time
divided by the average number of spikes over the same time? Or are
you counting just the thermodynamics of the axon and boutons?
> this is 1.9e-8 - 2.8e-5 W. So I
> get five-six order of magnitude for this with the most pessimistic
I'm not sure what you're comparing here, what a neuron could
accomplish if all of its energy input were used for computation rather
than metabolism (and minimal loss as heat)? Or are you suggesting
that there's energy loss somewhere else?
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