Re: microtubules and consciousness

From: Mitchell J Porter (mjporter@U.Arizona.EDU)
Date: Thu Jul 26 2001 - 13:09:17 MDT

On Thu, 26 Jul 2001, Ben Houston wrote:

> Mitchell,
> RE:
> I was looking through some work that you have done previously on the role
> that the quantum properties of microtubules play in consciousness (?).
> (Maybe you are not positing a role in consciousness for microtubules, but
> your coauthors seem to be suggesting it.) Myself I've never understood how
> this can play much of a role in anything that is unique to human
> consciousness or even primates near-consciousness since most other organisms
> with neurons (i.e. birds, reptiles, amphibians, and invertebrates) also have
> very similar microtubules.
> Just wondering since your sort of posting on this list right now. If you
> don't have time don't worry about it.

For me there are two issues. One is the simple question of fact as to
whether or not quantum coherence exists somewhere in the brain. The
other is whether it has anything to do with consciousness.

But first let's be a little clearer about the meaning of consciousness.
It can be used to mean awareness of oneself, or to mean awareness of
anything at all. Sophisticated self-awareness might be restricted to
a few big-brained species, but awareness may exist a long way down the
phylogenetic tree.

Starting with the second issue: for me, the existence of macroscopic
quantum states in the brain would make the unitary aspect of awareness
(its all-at-once-ness, the holistic simultaneity of experience...)
a little easier to understand. It wouldn't make *self*-awareness any
easier to understand - although if you think that all awareness is
grounded in some quantum phenomenon, you'll have to identify
self-awareness with some version of that phenomenon. But quantum
entanglement is a much stronger ontological tie than the famous
40 Hz synchronized firing which is the most popular solution to the
"binding problem". Synchronization can solve the problem of getting
two pieces of information to the same place at the same time, in an
otherwise asynchronous network, but it doesn't require us to think
of the synchronized neurons as a natural whole. But since entangled
quantum systems actually don't have individual states - only the
whole system does - there's a much stronger case for thinking of
two entangled things as one.

So that's some of my motivation. Now, if neural microtubules are
the locus of a macroscopic quantum state which in turn is the
locus of awareness, then yes, any peculiarities of human consciousness
have to be explained in terms of features unique to the human brain.
I think there's scope for that: there's more neurons, the cellular
environment is different, and human tubulins are that little bit
different from anything else, just like most genes in most species.
But remember that many things unique to humans may be explained
with reference to cognition, not consciousness, in which case it's
the larger stuff like architecture and connectivities which matters.

Anyway, however imponderable the philosophy may seem, the presence
or absence of quantum coherence should at least be calculable. So
that's what I work on: one class of models of quantum coherence in
the microtubule, somewhat different from the original Hameroff-Penrose
theory. Some time this year I hope to do the definitive decoherence
calculation for that class of models, to find out whether a quantum
state could last long enough to make a difference. If it makes
theoretical sense, then we can start looking for it. If not, I'll
move on to something else.

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