RE: Human-level CPU power crossover date

From: Dani Eder (
Date: Wed Apr 11 2001 - 12:39:25 MDT

> Fascinating. The intersynaptic cleft is a storm of
> neurotransmitters and
> assorted ions diffusing back and forth, not to
> mention the complex enzyme
> cycles inside the cells that affect and are affected
> by 'firing'. How do you
> collapse all that down to one bit?

The nature of the synapse (whether it is exitatory
or inhibatory, strength of the connection, etc.
Is probably more like a byte of data, but this value
changes slowly - the wiring pattern of the brain
does not change on a 10 ms time scale. A table of
synapse connections for a given neuron would take
a few bytes/synapse - mainly distance down the axon
in milliseconds and what target neuron the synapse
leads to, and what type of synapse connection.

The computation cycle would be something like:
  for each neuron
   -sum up synapse firings received from other
    neurons and determine whether to generate
    action potential
   -propagate action potential (if any)down axon,
    which amounts to updating a variable that
    tracks where the action potential is currently
   -set synapse firing to 1 if action potential
    has got to a particular synapse. Reset to
    0 if previously 1.

My estimate deals in order of magnitude values
of number of neurons in the brain, number of
synapses/neuron, and average firing rate. If it
really takes a byte of data per synapse firing
rather than a bit, that's within the tolerance
of my estimate. You might not have to model every
neuron and synapse in a human brain because of
built-in redundancy, and the fact that a lot of the
brain runs the body at levels below intelligence.
Maybe you have to model the whole brain plus the
rest of the central nervous system, and give it
a stream of inputs (sound, sight, touch, etc.) for
intelligence to work. Maybe the best way to build
an intelligence has nothing to do with modeling
neurons. So take my estimate as
being something like:

Dani Eder's guesstimate at the processing power
needed for a human-level AI is
10^17 bits/second +/- about 2 orders of magnitude.

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