[ExI] quantum brains
avantguardian2020 at yahoo.com
Sun Jan 24 01:07:56 UTC 2010
----- Original Message ----
> From: Stathis Papaioannou <stathisp at gmail.com>
> To: ExI chat list <extropy-chat at lists.extropy.org>
> Sent: Wed, January 20, 2010 12:35:50 AM
> Subject: Re: [ExI] quantum brains
> Penrose thinks there is an as yet undiscovered theory of quantum
> gravity which is uncomputable and which is an essential part of brain
I don't care what Penrose thinks except insofar as I agree that QM may play a role in brain function. Of course I have been of that opinion long before I heard of Penrose's theory, but that is not important. His reasoning for bringing quantum gravity into the picture eludes me except perhaps as a means to place his theory beyond the realm of experimental falsification. And of course the microtubules are a bizarre non-sequitor brought in by Hammeroff because like most molecular biologists, he thinks the protein or gene he is specialized in is the most important molecule in the world. So let's throw out the gravity, since astronauts in zero G don't get stupid or lose consciousness. And let's assume that microtubules are a structural component of the cytoskeleton and leave it at that. After all neurons are not particularly mobile for cells and if microtubules were the mechanism of consciousness, peoples would think with their muscles instead of
their brains because myocytes have more microtubules than neurons. And let's put off any conclusions regarding the computability or uncomputability of the brain until we have better defined the problem space and have more data. Let's just entertain the naked hypothesis that brains may utilize QM for some part of their function and see where it leads.
> We haven't been able to make self-repairing, self-replicating
> machines, and nature has been doing it for billions of years. It's
> possible that we will be able to upload minds before we can make
> artificial organisms. But that doesn't mean that vitalism is correct.
Nature hasn't been doing it for all those billions of years. Spontaneous generation of de novo life was experimentally falsified by Pasteur in the 19th century at least at the current conditions on planet earth. Nature need only have done it once in those billions of years and then those self-replicating machines did the rest. I have some unusual hypotheses about the origins of life too that I won't go into now. But I certainly don't see what vitalism has to do with this discussion.
> > That being said, there are a lot of parallels between how people and quantum
> particles behave. For one thing, they both behave probabilistically. One cannot
> predict a persons actions in response to a stimulus to the degree that one can
> predict say a falling brick, the oxidation of iron, or other straightfoward
> physical process. The best one can do is assign probabilities based on the
> previous history and the statistical analysis of large ensembles of similar
> people. While economists try to constrain predicted behavior by rationality,
> people, even rational people, can and do act irrationally under certain
> You could make the same analogy between quantum particles and any
> classical chaotic or truly random system.
Perhaps. But there are other parallels that don't apply to classical chaotic systems. Things like the mind:body -> quantum wavefunction:quantum information dualites that Serafino mentioned in his post to which one could add the more cliche wave:particle duality.
Then there is the way that excitory post-synaptic potentials (EPSP) and inhibitory post-synaptic potentials (IPSP) can sum over time and space to trigger neuronal depolarization that is very reminiscent of constructive and destructive interference. Although by my cursory swim through the literature, reports are all over the board with the quantitative measurements of these things, the mean voltages of these signals are approximately 5 millivolts and the mean current is about 25 picoamps. The average duration of these signals are about 20 milliseconds. Multiply all these rough figures together and you get approximately 2.5 femtojoules or about 15,600 eV which is admittedly too much energy for quantum effects.
However there are EPSP that fire spontaneously at a much smaller voltage called miniature EPSPs or mEPSPs that are in range of about 400 microvolts, 10 picoamps, and last about 1 millisecond. These are thought to be caused by single vessicles of neurotransmitters being randomly being released into the synaptic cleft. These things have an energy of about 25 eV which for comparison is not much higher than the ground state of the hydrogen atom at -13.6 eV. Moreover these things happen quite frequently.
Now it seems to me that these mEPSPs in the brain are very similar to the quantum fluctuations in normal matter. Like the fluctuations in a nebula of hydrogen gas that could trigger the condensation of the gas into a protostar. Since EPSP are additive, one or more of these things could push a subthreshold normal EPSP over the threshold causing a recipient neuron to depolarize and initiate an action potential. So this is a potential mechanism for leaps of intuition, hunches, imagination, and creativity. And it seems a much more testable hypothesis than quantum microgravity yanking on microtubules ala Penrose and Hammeroff. Now the interesting question is are these things capable of the more bizzare quantum behavior like uncertainty, entanglement, and wave-particle duality? e.g. could mEPSPs interfere with themselves? Or might they exhibit particle properties and be called "psions"?
"Never express yourself more clearly than you think." - Niels Bohr
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