[ExI] Smallest human-equivalent device

John Clark johnkclark at gmail.com
Sun Oct 13 16:04:48 UTC 2013

On Sat, Oct 12, 2013 at 1:36 PM, Anders Sandberg <anders at aleph.se> wrote:

> How many transistors are functionally equivalent to one synapse?

I don’t know but I can figure out how many modern transistors you could fit
inside 2 neurons. The average human brain is about 1450 cubic centimeters
or 1.45*10^24 cubic nanometers. There are about 10^11 neurons in the brain
so each neuron and its accompanying support structures ( glial cells,
capillaries etc) occupies about 1.45* 10^13 cubic nanometers, but you need
2 neurons to make a synapse so that’s 2.9*10^13 cubic nanometers. Using
technology that Intel will mass produce next year they can  build a
transistor inside a 3*10^3 cubic nanometer box, or about 10^10 transistors
in the volume occupying 2 neurons. And I don’t think the fact that those 10
billion transistors are operating nearly a billion times faster than
neurons can is a insignificant consideration.

Granted you couldn’t (yet) pack transistors at that density throughout a
volume as large as the human brain due to heat considerations, but imagine
what will be practical in just a few years.

> > Clearly we need to at least be able to add a synaptic weight to some
> other state variable, and this variable needs to have at least a few bits
> of resolution.


>  > Doing this with transistors requires more than one (28 transistors for
> a full adder,

OK, so if 99.99999% of the volume inside that brain sized 1450 cubic
centimeter cavity inside the skull was just empty space to deal with the
heat problem you'd still have more than enough transistors to give that
synapse an adder. And yes I know that a neuron has more than one synapse,
but it doesn't have a billion of them, and transistors are very fast, a lot
faster than neurons.  And all this is with just 2014 technology.

 John K Clark
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