The Frontal Cortex

Quantum Consciousness

Do any neuroscientists actually take Roger Penrose’s theory of quantum microtubules seriously? When I hear phrases like “quantum Platonic non-computational influences” being applied to the brain, I tend to get very sleepy. But Andrew Sullivan, in a post titled “The Big Wow,” recently featured a long letter laying out Penrose’s latest musings on the quantum nature of consciousness, life after death, etc. I haven’t looked at The Emperor’s New Mind for several years, but Penrose’s new version of the theory sounds even more improbable than I remember.

I have a feeling that the attractiveness of Penrose’s theory is inversely related to your knowledge of microtubules. If you’ve got a naive interest in all things quantum, but know little about neurons, then Penrose’s theory must seem like an obvious answer to an intractable biological problem. Just add quantum fuzziness! I also found this skeptical reaction by a physicist rather interesting:

Based on a calculation of neural decoherence rates, we argue that that the degrees of freedom of the human brain that relate to cognitive processes should be thought of as a classical rather than quantum system, i.e., that there is nothing fundamentally wrong with the current classical approach to neural network simulations. We find that the decoherence timescales ~10^{-13}-10^{-20} seconds are typically much shorter than the relevant dynamical timescales (~0.001-0.1 seconds), both for regular neuron firing and for kink-like polarization excitations in microtubules. This conclusion disagrees with suggestions by Penrose and others that the brain acts as a quantum computer, and that quantum coherence is related to consciousness in a fundamental way.

This is one of the more frustrating aspects of scientific theories of consciousness. At a certain point, they all seem hopelessly improbable, and so we let unfounded theories like quantum microtubules linger around.


  1. #1 Mustafa Mond, FCD
    March 15, 2007

    Yeah, if you’ve got a little time and feel like torturing your brain cells, watch Stuart Hameroff deliver the quantum consciousness party line at Beyond Belief 2006, with actual physicists in the audience. The Q&A session following the talk is pretty good.
    Session 4.

  2. #2 Jonathan Vos Post
    March 15, 2007

    I allegedly had a paper on biophysics of non-steady-state biological “AC Chemistry” [a term that I coined before it was apparently rediscovered published and elsewhere] in a Proceedings of a Stuart Hameroff-led NATO Conference somewhere in the 1979-1984 era. But none of the companies for whom I worked then and in the next few years (Boeing, Rockwell) had technical librarians who could find the citation, let alone a copy of the proceedings.

    Anyone with microtubules of either quantum or classical nature in their brains have an idea?

    And with what kind of tiles are Penrose’s bathrooms tiled? We know about the toilet paper design that he copyrighted, and defended against intelletcual property theft.

    And have you seen the recent Science article with lovely photos and diagrams of those 500-year-old Penrose tiles in Islamic architecture? It’s better than the newspaper versions.

  3. #3 Suraj
    March 15, 2007

    A very timely article indeed, Jonah…

    Coming to think of quantum reality..why is it always at loggerheads with cosmology and classical physics.?
    Its just because of one reason – probabilities of events at quantum levels require a conscious observer to collapse..!
    That famous cat of Schrodinger can be considered “alive” only if some conscious observer peaked into the box thereby collapsing all the probability waves to the “alive” point, rather than the “dead” point. Think of every electron in this universe (including your bodies) requiring such an observer for their probability waves to collapse ! That would mean, the absence of such an all pervading conscious observer would literally “smudge” us all up into probability waves..!!
    What Penrose has now been trying is to sneak into neuroscience, this irritating mathematical incoherence of current theoretical physics..!

    To explain the conundrum, physicists require an all pervading “godly” consciousness embedded within the stuff of the universe. And it makes things a lot more easier..but for the neurobiologist who dreams of a final theory of “consciousness” and “self” , things get out of control, as this new idea of “embedded consciousness” pose ever greater challenges to his dreams.

    Its also noteworthy that many of these ideas of inherent universal consciousness, recycling consciousness, reincarnations of memories and thoughts, a self-aware universe are all topics discussed in the 2000+ year-old Indian religious philosophy books like the Vedas and Upanishads. The universe in these philosophical texts is described as having originated from a big explosion, and is imagined as self-aware; the laws of nature being described as the multidimensional reflections of the “divine”.

    Any one reading Fritjof Capra here.? 🙂

  4. #4 DavidD
    March 15, 2007

    The first comment following the talk Mustafa Mond mentioned came from physicist Lawrence Krauss, From a physics perspective, everything you say is nonsense, and maybe Im being too polite. A few specific objections followed.

    My take on listening to such claims as quantum consciousness is how much more metaphor than science it is. Yes there’s correlation between what the front of the brain is doing and the back of the brain, but tell me again more slowly how quantum entanglement is the best explanation for that?

    It’s like the Law of Attraction that some New Age believers like so much, which says that whatever you think about will come your way, because of how electromagnetism takes your thoughts out into the world to reel in whatever it is. This was on Larry King on CNN on March 8. Larry asked one of the “experts” if this was scientifically sound. Of course it is, said the guest. Right. The thing is that I’m sure there is something real to our attention bringing us closer to whatever the object of our attention is, sometimes, just as the activity of the front of our brain correlates somewhat with the back of our brain, but it’s not electromagnetism behind the former nor quantum entanglement behind the latter. In each case the neurophysiology of it is both complicated and less than an absolute thing.

    I’m sure it’s human nature that likes simpler explanation, even for Roger Penrose and Stuart Hameroff. Now how does one convince them of that? I wonder if there’s any fMRI protocol that can reveal oversimplification? That’s my oversimplification. But I could be talked out of it easily, not so those guys on Larry King.

  5. #5 Erin Oakman
    March 15, 2007

    Dont’ be too quick to dismiss HAMEROFF-PENROSE ideas, which have not been properly disproved. I saw Hameroff butcher the Beyond Belief Q&A– and Lawrence Krauss reaction left me even more curious about Hameroff . . .

    Penrose wrote about plasticity as the growth and contraction of dendritic spines. Where do microtubules come in? Microtubules are important for gap junctions, especially dendritic-dendritic gap junctions between spines. Microtubules grow out of lamellar bodies, which are located in the main dendrite adjacent to the gap junctions in spines. Lamellar bodies form near cells that are forming gap junctions. For example, there is a high density of lamellar bodies in the inferior olive, a site of prevalent gap junction communication.

    When considering brain plasticity, Penrose imagined that some structural element of the nervous system would grow and shrink like a quasicrystal, but he did not name microtubules as a structural element of the quasicrystal. It is not too speculative for Hameroff to think that microtubules have a role in the expansion and contraction of dendritic spines. At any rate, gap junctions and microtubules are interesting.

  6. #6 Jonathan Vos Post
    March 16, 2007

    Check out the microtubules in this amazing “photograph”:

    An Architectural Plan Of The Cell

  7. #7 Jake Young
    March 16, 2007

    My take on listening to such claims as quantum consciousness is how much more metaphor than science it is. Yes there’s correlation between what the front of the brain is doing and the back of the brain, but tell me again more slowly how quantum entanglement is the best explanation for that?

    In the behavioral neuroscience field we talk about coherence a fair bit, but it is has a very specific definition. It relates to when you are recording in two areas and those areas become synchronized. We infer things about what this synchronization from the animals behavior.

    But this is not coherence like quantum coherence. For one, it doesn’t happen instantaneously. For two, it almost certainly takes energy to bring the two parts of the brain — we would say “neural systems” — online in this way.

    This makes the quantum coherence metaphor relevant only in the sense that it also contains the word “coherence”, but it isn’t really useful otherwise.

    As an added point, we still don’t understand a lot about how information is coded in the brain, so we don’t understand whether this coherence represents something important. If, for example, synchrony to the theta rhythym (a rhythym found in hippocampal firing) occurs does this mean the brain is using information from the hippocampus? Who knows.

    Last thing. This reminds me of a fad in neuroscience about 50 years ago when it was discovered that neurons in the retina could code different frequencies of diffraction gratings. (It was later discovered that this phenomenon represented center-surround visual fields.) Suddenly everyone was talking about how the brain was performing some elaborate Fourier transform, and everything in the brain was frequencies. It seems absurd now, but people actually bought it from that one experiment.

  8. #8 Jake Young
    March 16, 2007

    Actually, rereading the quote from the physicist in the original post, he is basically making the point about quantum coherence being infinitely faster already. Only he uses numbers… 🙂

  9. #9 Torbjrn Larsson
    March 16, 2007

    Dont’ be too quick to dismiss HAMEROFF-PENROSE ideas, which have not been properly disproved.

    I go with Krauss on this one. Tegmark showed conclusively that no process in microtubules can act before decoherence sets in.

    There are no reasons classical processes aren’t sufficient, and the above conclusions from theory agrees that it must be so. Of course, that doesn’t mean there will be no surprises.

  10. #10 Neil B ?
    December 27, 2008

    Decoherence is a fallacious argument anyway and does not solve the quantum measurement problem. It is wrong to just stick that portion of probability deriving from squared moduli into the DM “to start with” as done in decoherence arguments. Those probabilities are supposedly what you are trying to explain from superposed states in evolution, you can’t just take the desired outcome and stick it into the alleged mechanism first – that would be a classic “circular argument.” So it’s no surprise, when you make a circular argument (“cheating” in the logic: unintentional of course and a common temptation, but still fallacious) it seems to derive exclusionary probabilities instead of coexisting states (like “alive and “dead” cat), because you already put them there at the start! That’s no valid way to “explain” how or why something happens. The mystery of collapse remains, and thus perhaps of consciousness as well. See also

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