[extropy-chat] Desirability of Singularity (was Are ancestor simulations immoral?)

[Martin Striz]

On 6/5/06, Damien Sullivan <phoenix at ugcs.caltech.edu> wrote:

> The brain is 2% of body mass but 20% of body heat; I expect most of the
> energy is being used for computation, or to maintain readiness to
> compute.  Of course this might be in neurotransmitter recyling as well
> as in spike trains.

That's a different claim from the one that I typically hear, "the
brain is 2% of body mass but consumes 20% of the energy."  It also
consumes 40% of serum glucose, but that shouldn't be  surprising since
glucose metabolism is turned off in neurons.

But to answer your question, here's one analysis:

http://striz.org/docs/neuron-energy-budget.pdf

The resting state consumes 13% of the energy (which probably includes
background metabolism, gene expression, etc.), while 87% is in one way
or another involved in signaling (firing, postsynaptic activity, and
neurotransmitter recycling).  It should be noted that glutamatergic
neurons were used for this analysis, but they constitute the major
excitatory circuits in the brain.

I must admit, the percentage is higher than I had expected.  Half of
the genes in the genome are expressed in the brain, so I would have
expected more energy to be used during resting state activities.

Martin