Re: Microtubules, coherence, consciousness

Date: Fri, 16 Feb 1996 14:47:55 -0800
From: Paul Wilkens <paul@reed.edu>
To: quantum-d@teleport.com
Subject: Re: Microtubules, coherence, consciousness

with reference to:
http://www.teleport.com/~rhett/quantum-d/posts/srh_2-09-96.html

Stuart Hameroff wrote:

>Stan Klein claims that for quantum theory to be relevant to
>consciousness "what is needed for the brain are superpositions of a
>neuron firing |F> AND a neuron not firing |NF>". And indeed, the notion
>of all-or-none, membrane mediated neural firing being the ONLY
>significant level of information signaling and processing in the brain
>IS the accepted conventional wisdom in cognitive science, neuroscience
>and philosophy. Each neuron, however, is so incredibly complex that
>this notion should be recognized as a gross oversimplification, if not
>delusion. Future developments in technology will bear this out.

        this description of neural computation is very removed from
concrete knowledge. while an action potential may be an all-or-nothing
event, the brain does NOT operate on digital principles. almost all
CNS neurons use action potentials convey information through frequency
and pattern, and an event conveys no information without the context
of its surrounding events. the overall spatio-temporal pattern is of
the utmost importance, both in neural networks, and in the
computational summation of the post-synaptic cell. it is not helpful
to construe biological computation as less complicated than it
actually is, regardless of any quantum abstractions.

>Unlike the random, "subjective reduction" (SR, or R) of standard
>quantum theory caused by observation or environmental entanglement, the
>OR we propose in microtubules is a self-collapse and it results in
>particular patterns of microtubule-tubulin conformational ("eigen-")
>states that regulate neuronal activities including synaptic functions.
>Possibilities and probabilities for post-reduction tubulin states are
>influenced by factors including attachments of microtubule-associated
>proteins (MAPs) acting as "nodes" which tune and "orchestrate" the
>quantum oscillations. We thus term the particular self-tuning OR
>process in microtubules "orchestrated objective reduction" ("Orch OR"),
>and calculate an estimate for the number of tubulins (and neurons)
>whose coherence for relevant time periods (e.g. 500 milliseconds) will
>elicit Orch OR. We calculate an estimate of 10^9 tubulins, equivalent
>to a range of from hundreds to ten thousand neurons, as the number
>required for a 500 msec conscious event. A "more intense" conscious
>event, for example one which emerges in only 50 msec, would require
>10^10 tubulins. Any Orch OR  would "bind" varying time scale processes,
>so that a particular conscious event can include various contents
>emerging over differing time scales (for example responding to an
>immediate situation, and recalling an overdue bill).

        the idea of coherent quantum states leading to a real neural
events is quite attractive. however, i don't quite understand the way
this event is presented. when do neurons fire? when microtubules
attain coherence, all happily postulating possible states in infinite
universes, they must choose a particular state to collapse to. when
this happens, does this mean that their neurons reenact, in ionic
potential, the exact state that the microtubules envisioned? if so,
how do we know if microtubules did anything at all, if the end state
is merely another electrical pattern, one that would have occurred
anyway by normal means? also, i believe that the brain would still be
active during the 500 milliseconds that coherence takes. coherent
microtubules must carry out their global tasks inside neurons that are
always busy conducting the local business of the brain. neurons don't
stop summing PSPs unless they are dead, and they don't stop receiving
them unless their afferents are dead. doesn't the constant electrical
flux interfere with the microtubules? surely they must need some time,
free of interference, to produce their global configurations?

        the brain is dynamic and local. that it acts globally is
amazing, and i certainly do not suggest that traditional neuroscience
contains all the answers, but i do think any theory of quantum
cogitation should at least consider the macroscopic events that are
known to constitute the gross physical aspects of brain function.


paul