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Quantum Consciousness: What Do We Know?

by Stuart Hameroff

A Reply to Quantum Quackery by Michael Shermer

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Stuart Hameroff M.D. is:
Professor, Departments of Anesthesiology and Psychology
Director, Center for Consciousness Studies, The University of Arizona, Tucson, Arizona

I read with interest Michael Shermer’s skeptical criticism of the surprise hit film What the #$*! Do We Know? (Whatthebleep? to its fans) in which I appear.1 The film attempts to link consciousness with the weirdness of quantum mechanics. As the best candidate for such a connection, Shermer cites (then attempts to refute) a theory put forth a decade ago by British physicist Sir Roger Penrose and me. 2

We attribute consciousness to quantum computation in structural proteins within the brain’s neurons called microtubules. Though Shermer correctly describes microtubules — part of the cell’s cytoskeleton — as scaffolding, they also actively organize intra-cellular movement, transport and neuronal synaptic plasticity (the apparent cornerstone of learning and memory). How are such activities organized? Pondering the amazing feats of unicellular protozoa which swim, avoid predators, learn, find food and mates and have sex — all without benefit of a single synapse — the famed neuroscientist Charles Sherrington surmised a half century ago “of nerve there is no trace, but the cytoskeleton might serve”. Indeed, cytoskeletal microtubules’ periodic lattice structure (resembling switching circuits in computers) seems ideally suited to molecular-scale computation.

The states of microtubule protein subunits (bits in a microtubule computer) are regulated by quantum mechanical (van der Waals London) forces in intra-protein non-polar pockets, suggesting that microtubule subunits could act not only like classical bits, but also like quantum bits (qubits) in quantum computers.

To debunk our theory Shermer cites an assertion in a book by Victor Stenger that the product of mass, velocity and distance of a quantum system cannot exceed Planck’s constant. I’ve not seen this proposal in a peer reviewed journal, nor listed anywhere as a serious interpretation of quantum mechanics. But in any case Stenger’s assertion is disproved by Anton Zeilinger’s experimental demonstration of quantum wave behavior in fullerenes and biological porphyrin proteins. (Skepticism should cut both ways, Mr. Shermer.) Nonetheless I agree with Stenger that synaptic chemical transmission between neurons is completely classical. The quantum computations we propose are isolated in microtubules within neurons. Classical neurotransmission provides inputs to, and outputs from, microtubule quantum computations mediating consciousness in neuronal dendrites.

But the brain seems far too warm for significant quantum states, apparently running into the problem of decoherence. (Shermer conflates the strong Copenhagen interpretation of the measurement problem—that conscious observation causes wave function collapse, with decoherence—in which any exchange of energy or information with the environment erodes a quantum system.) But recent evidence shows that quantum processes in biological molecules are actually enhanced at higher temperatures. Moreover biological mechanisms within neurons (actin gelation, laser-like metabolic pumping, plasma layer shielding and topological quantum error correction in/around microtubules) may preserve quantum states in microtubules for hundreds of milliseconds or longer at brain temperature.

Is there any evidence for the relevance of quantum states/processes to consciousness? Well, general anesthetic gases selectively erase consciousness while nonconscious brain activities continue (e.g. evoked potentials, control of autonomic function, EEG). The anesthetic gases act in the same intra-protein non-polar pockets in which quantum London forces control protein conformation. This occurs in a class of receptors, channels and other brain proteins including cytoskeletal structures. And the anesthetics do so by forming only quantum mechanical interactions, presumably interfering only with physiological quantum effects. It is logical to conclude that consciousness occurs in quantum pockets within proteins throughout the brain.

Shermer also conflates the Copenhagen interpretation with the dualist quantum mind proposal of Sir John Eccles. Suffice to say that in the Penrose-Hameroff model, consciousness does not cause collapse of the quantum wave function (a la Copenhagen). Rather, consciousness is collapse. More precisely, consciousness is a particular type of self-collapse proposed by Penrose involving quantum gravity (currently being tested). Pre-conscious (unconscious/subconscious) information exists as quantum superpositions—multiple coexisting possible actions or experiences—which, upon reaching a specified threshold at the moment of consciousness/self-collapse, choose a particular action or experience. Such conscious moments are calculated to occur roughly 40 times per second.

Shermer closes by advising researchers to look for emergence of consciousness at the neural level and higher. This has been precisely the tack taken by armies of scientists and philosophers for decades, and the result is nil. Consciousness is ever more elusive. The prevalent paradigm—that axonal action potentials and chemical synaptic transmissions are fundamental units of computation from which consciousness emerges at a higher-order network level—force-fits consciousness into an illusory, out-of-the-loop epiphenomenon. While this might be true, the prevalent paradigm is also incompatible with the best electrophysiological correlate of consciousness—synchronized gamma EEG (“coherent 40 Hz” oscillations). The latter, it turns out, is mediated by coherent activities of neuronal dendrites linked by electrotonic gap junctions, windows which link adjacent neurons (and glia) into large-scale syncytia, or “hyper-neurons”.

In 1998 I published a list of twenty testable predictions of our model (which, unlike prevalent emergence theories, is falsifiable). Several predictions have proven true (e.g. signaling and action of psychoactive drugs in microtubules). To explain the extension of quantum states among many neurons throughout the brain, I also predicted that neurons connected by gap junctions mediate consciousness, subsequently validated by gamma EEG studies. That doesn’t prove that quantum states extend among neurons (e.g. by tunneling through gap junctions), but it casts serious doubt on conventional approaches (which have yet to generate a testable prediction). Skeptics like Shermer should apply their craft to conventional dogma as well as to upstart hypotheses.

Regarding the film, I stand by my statements (Shermer didn’t criticize anything I said). But Whatthebleep? is entertainment. Lighten up! The early animations of Jules Verne’s moon landings were crude by later standards, but planted the seed of a wonderful idea in popular culture.

1. Shermer M (2005) Quantum Quackery, Scientific American 292(1):34
2. Penrose Sir R Shadows of the Mind Oxford University Press, 1994

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