Orchestrated objective reduction
Orchestrated objective reduction (Orch OR) is a biological theory of mind that postulates that consciousness originates at the quantum level inside neurons, rather than the conventional view that it is a product of connections between neurons. The mechanism is held to be a quantum process called objective reduction that is orchestrated by cellular structures called microtubules. It is proposed that the theory may answer the hard problem of consciousness and provide a mechanism for free will. The hypothesis was first put forward in the early 1990s by theoretical physicist Roger Penrose and anaesthesiologist and psychologist Stuart Hameroff. The hypothesis combines approaches from molecular biology, neuroscience, quantum physics, pharmacology, philosophy, quantum information theory, and quantum gravity.
While mainstream theories assert that consciousness emerges as the complexity of the computations performed by cerebral neurons increases, Orch OR posits that consciousness is based on non-computable quantum processing performed by qubits formed collectively on cellular microtubules, a process significantly amplified in the neurons. The qubits are based on oscillating dipoles forming superposed resonance rings in helical pathways throughout lattices of microtubules. The oscillations are either electric, due to charge separation from London forces, or magnetic, due to electron spin—and possibly also due to nuclear spins (that can remain isolated for longer periods) that occur in gigahertz, megahertz and kilohertz frequency ranges. Orchestration refers to the hypothetical process by which connective proteins, such as microtubule-associated proteins (MAPs), influence or orchestrate qubit state reduction by modifying the spacetime-separation of their superimposed states. The latter is based on Penrose's objective-collapse theory for interpreting quantum mechanics, which postulates the existence of an objective threshold governing the collapse of quantum-states, related to the difference of the space-time curvature of these states in the universe's fine-scale structure.
Orch OR has been criticized from its inception by mathematicians, philosophers, and scientists, prompting the authors to revise and elaborate many of the theory's peripheral assumptions, while retaining the core hypothesis. The criticism concentrated on three issues: Penrose's interpretation of Gödel's theorem; Penrose's abductive reasoning linking non-computability to quantum processes; and the brain's unsuitability to host the quantum phenomena required by the theory, since it is considered too "warm, wet and noisy" to avoid decoherence. In other words, there is a missing link between physics and neuroscience in the pursuit of a theory of everything. However, some evidence has been produced in recent years.
In 1931, mathematician and logician Kurt Gödel proved that any effectively generated theory capable of proving basic arithmetic cannot be both consistent and complete. In other words, a mathematically sound theory lacks the means to prove itself. An analogous statement has been used to show that humans are subject to the same limits as machines. However, in his first book on consciousness, The Emperor's New Mind (1989), Roger Penrose argued that Gödel-unprovable results are provable by human mathematicians. He takes this disparity to mean that human mathematicians are not describable as formal proof systems, and are therefore running a non-computable algorithm.
If correct, the Penrose–Lucas argument leaves the question of the physical basis of non-computable behaviour open. Most physical laws are computable, and thus algorithmic. However, Penrose determined that wave function collapse was a prime candidate for a non-computable process. In quantum mechanics, particles are treated differently from the objects of classical mechanics. Particles are described by wave functions that evolve according to the Schrödinger equation. Non-stationary wave functions are linear combinations of the eigenstates of the system, a phenomenon described by the superposition principle. When a quantum system interacts with a classical system—i.e. when an observable is measured—the system appears to collapse to a random eigenstate of that observable from a classical vantage point.
If collapse is truly random, then no process or algorithm can deterministically predict its outcome. This provided Penrose with a candidate for the physical basis of the non-computable process that he hypothesized to exist in the brain. However, he disliked the random nature of environmentally induced collapse, as randomness was not a promising basis for mathematical understanding. Penrose proposed that isolated systems may still undergo a new form of wave function collapse, which he called objective reduction (OR).
Penrose sought to reconcile general relativity and quantum theory using his own ideas about the possible structure of spacetime. He suggested that at the Planck scale curved spacetime is not continuous, but discrete. He further postulated that each separated quantum superposition has its own piece of spacetime curvature, a blister in spacetime. Penrose suggests that gravity exerts a force on these spacetime blisters, which become unstable above the Planck scale of and collapse to just one of the possible states. The rough threshold for OR is given by Penrose's indeterminacy principle:
- is the time until OR occurs,
- is the gravitational self-energy or the degree of spacetime separation given by the superpositioned mass, and
- is the reduced Planck constant.
Thus, the greater the mass-energy of the object, the faster it will undergo OR and vice versa. Atomic-level superpositions would require 10 million years to reach OR threshold, while an isolated 1 kilogram object would reach OR threshold in 10−37s. Objects somewhere between these two scales could collapse on a timescale relevant to neural processing.[additional citation(s) needed]
An essential feature of Penrose's theory is that the choice of states when objective reduction occurs is selected neither randomly (as are choices following wave function collapse) nor algorithmically. Rather, states are selected by a "non-computable" influence embedded in the Planck scale of spacetime geometry. Penrose claimed that such information is Platonic, representing pure mathematical truth, aesthetic and ethical values at the Planck scale. This relates to Penrose's ideas concerning the three worlds: the physical, the mental, and the Platonic mathematical world.[additional citation(s) needed]
The Penrose–Lucas argument was criticized by mathematicians, computer scientists, and philosophers, and the consensus among experts in these fields is that the argument fails, with different authors attacking different aspects of the argument. Minsky argued that because humans can believe false ideas to be true, human mathematical understanding need not be consistent and consciousness may easily have a deterministic basis. Feferman argued that mathematicians do not progress by mechanistic search through proofs, but by trial-and-error reasoning, insight and inspiration, and that machines do not share this approach with humans.
Penrose outlined a predecessor to Orch OR in The Emperor's New Mind, coming to the problem from a mathematical viewpoint and in particular Gödel's theorem, but lacked a detailed proposal for how quantum processes could be implemented in the brain. Stuart Hameroff separately worked in cancer research and anesthesia, which gave him an interest in brain processes. Hameroff read Penrose's book and suggested to him that microtubules within neurons were suitable candidate sites for quantum processing, and ultimately for consciousness. Throughout the 1990s, the two collaborated on the Orch-OR theory, which Penrose published in Shadows of the Mind (1994).
Hameroff's contribution to the theory derived from his study of the neural cytoskeleton, and particularly on microtubules. As neuroscience has progressed, the role of the cytoskeleton and microtubules has assumed greater importance. In addition to providing structural support, microtubule functions include axoplasmic transport and control of the cell's movement, growth and shape.
Orch OR combines the Penrose–Lucas argument with Hameroff's hypothesis on quantum processing in microtubules. It proposes that when condensates in the brain undergo an objective wave function reduction, their collapse connects noncomputational decision-making to experiences embedded in spacetime's fundamental geometry. The theory further proposes that the microtubules both influence and are influenced by the conventional activity at the synapses between neurons.
Hameroff proposed that microtubules were suitable candidates for quantum processing. Microtubules are made up of tubulin protein subunits. The tubulin protein dimers of the microtubules have hydrophobic pockets that may contain delocalized π electrons. Tubulin has other, smaller non-polar regions, for example 8 tryptophans per tubulin, which contain π electron-rich indole rings distributed throughout tubulin with separations of roughly 2 nm. Hameroff claims that this is close enough for the tubulin π electrons to become quantum entangled. During entanglement, particle states become inseparably correlated.
Hameroff originally suggested in the fringe Journal of Cosmology that the tubulin-subunit electrons would form a Bose–Einstein condensate. He then proposed a Frohlich condensate, a hypothetical coherent oscillation of dipolar molecules. However, this too was rejected by Reimers' group. Hameroff then responded to Reimers. "Reimers et al have most definitely NOT shown that strong or coherent Frohlich condensation in microtubules is unfeasible. The model microtubule on which they base their Hamiltonian is not a microtubule structure, but a simple linear chain of oscillators." Hameroff reasoned that such condensate behavior would magnify nanoscopic quantum effects to have large scale influences in the brain.
Hameroff proposed that condensates in microtubules in one neuron can link with microtubule condensates in other neurons and glial cells via the gap junctions of electrical synapses. Hameroff proposed that the gap between the cells is sufficiently small that quantum objects can tunnel across it, allowing them to extend across a large area of the brain. He further postulated that the action of this large-scale quantum activity is the source of 40 Hz gamma waves, building upon the much less controversial theory that gap junctions are related to the gamma oscillation.
In 1998, Hameroff made eight probable assumptions and 20 predictions to test the proposal. In 2013, Anirban Bandyopadhyay of the Japanese National Institute for Materials Science detected quantum states in microtubules. Penrose and Hameroff reported that Bandyopadhyay's experiments supported six out of the 20 theses, while invalidating none of the others. They subsequently responded to several critiques.
In 2015, physicist Matthew Fisher of the University of California, Santa Barbara proposed that the nuclear spins in phosphorus atoms could become entangled, preventing the information loss of decoherence and enabling quantum computation within the brain. The FELIX experiment has also been suggested to evaluate and measure the criterion of orchestrated objective reduction.
Decoherence in living organismsEdit
In 2000 Tegmark claimed that any quantum coherent system in the brain would undergo effective wave function collapse due to environmental interaction long before it could influence neural processes (the "warm, wet and noisy" argument, as it was later came to be known). He determined the decoherence timescale of microtubule entanglement at brain temperatures to be on the order of femtoseconds, far too brief for neural processing. Christof Koch and Klaus Hepp also agreed that quantum coherence does not play, or does not need to play any major role in neurophysiology. Koch and Hepp concluded that ``The empirical demonstration of slowly decoherent and controllable quantum bits in neurons connected by electrical or chemical synapses, or the discovery of an efficient quantum algorithm for computations performed by the brain, would do much to bring these speculations from the ‘far-out’ to the mere ‘very unlikely’.''
In response to Tegmark's claims, Hagan, Tuszynski and Hameroff claimed that Tegmark did not address the Orch-OR model, but instead a model of his own construction. This involved superpositions of quanta separated by 24 nm rather than the much smaller separations stipulated for Orch OR. As a result, Hameroff's group claimed a decoherence time seven orders of magnitude greater than Tegmark's, although still far below 25 ms. Hameroff's group also suggested that the Debye layer of counterions could screen thermal fluctuations, and that the surrounding actin gel might enhance the ordering of water, further screening noise. They also suggested that incoherent metabolic energy could further order water, and finally that the configuration of the microtubule lattice might be suitable for quantum error correction, a means of resisting quantum decoherence.
Since the 1990s numerous counter-observations to the "warm, wet and noisy" argument existed at ambient temperatures, in vitro and in vivo (i.e. photosynthesis, bird navigation). For example, Harvard researchers achieved quantum states lasting for 2 sec at room temperatures using diamonds. Plants routinely use quantum-coherent electron transport at ambient temperatures in photosynthesis. In 2014, researchers used theoretical quantum biophysics and computer simulations to analyze quantum coherence among tryptophan π resonance rings in tubulin. They claimed that quantum dipole coupling among tryptophan π resonance clouds, mediated by exciton hopping or Forster resonance energy transfer (FRET) across the tubulin protein are plausible.
In 2007, Gregory S. Engel, Professor in Chemistry at The University of Chicago, claimed that all arguments concerning the brain being "too warm and wet" have been dispelled, as multiple "warm and wet" quantum processes have been discovered.
In 2009, Reimers et al. and McKemmish et al., published critical assessments. Earlier versions of the theory had required tubulin-electrons to form either Bose–Einsteins or Frohlich condensates, and the Reimers group claimed that these were experimentally unfounded. Additionally they claimed that microtubules could only support 'weak' 8 MHz coherence. The first argument was voided by revisions of the theory that described dipole oscillations due to London forces and possibly due to magnetic and/or nuclear spin cloud formations. On the second issue the theory was retrofitted so that 8 MHz coherence is sufficient to support the whole Orch-OR hypothesis.
McKemmish et al. made two claims: that aromatic molecules cannot switch states because they are delocalised; and that changes in tubulin protein-conformation driven by GTP conversion would result in a prohibitive energy requirement. Hameroff and Penrose responded to the first claim by stating that they were referring to the behaviour of two or more electron clouds, inherently non-localised. For the second claim they stated that no GTP conversion is needed since (in that version of the theory) the conformation-switching is not necessary, replaced by oscillation due to the London forces produced by the electron cloud dipole states.
Hameroff's 1998 hypothesis required that cortical dendrites contain primarily 'A' lattice microtubules, but in 1994 Kikkawa et al. showed that all in vivo microtubules have a 'B' lattice and a seam.
Orch OR also required gap junctions between neurons and glial cells, yet Binmöller et. al. proved in 1992 that these don't exist in the adult brain. In vitro research with primary neuronal cultures shows evidence for electrotonic (gap junction) coupling between immature neurons and astrocytes obtained from rat embryos extracted prematurely through Cesarean section, however, the Orch-OR claim is that mature neurons are electrotonically coupled to astrocytes in the adult brain. Therefore, Orch OR contradicts the well-documented electrotonic decoupling of neurons from astrocytes in the process of neuronal maturation, which is stated by Fróes et al. as follows: "junctional communication may provide metabolic and electrotonic interconnections between neuronal and astrocytic networks at early stages of neural development and such interactions are weakened as differentiation progresses."
In 2001, Hameroff further proposed that microtubule coherence spreads between different neurons via dendritic lamellar bodies (DLBs) that are connected directly with gap junctions. De Zeeuw et al. had already proved this to be impossible in 1995, by showing that DLBs are located micrometers away from gap junctions.
In 2014, Bandyopadhyay et. al. speculated that microtubule-based quantum coherence can extend between different neurons if their notion of wireless transmission of information globally across the entire brain is proven. Hameroff and Penrose doubt whether such a wireless transmission would be capable of transmitting superimposed quantum-states and stick to their original gap junction proposal.
Hameroff speculated that visual photons in the retina are detected directly by the cones and rods instead of decohering and subsequently connect with the retinal glia cells via gap junctions, but this too was falsified.
Other biology-based criticisms have been offered. Papers by Georgiev point to problems with Hameroff's proposals, including a lack of explanation for the probabilistic release of neurotransmitter from presynaptic axon terminals and an error in the calculated number of the tubulin dimers per cortical neuron. Hameroff insisted in a 2013 interview that those falsifications were invalid, but did not provide any explanation where the falsifications fail.
- Hameroff, Stuart; Penrose, Roger (March 2014). "Consciousness in the universe: A review of the 'Orch OR' theory". Physics of Life Reviews. Elsevier. 11 (1): 39–78. Bibcode:2014PhLRv..11...39H. doi:10.1016/j.plrev.2013.08.002. PMID 24070914. Retrieved 6 December 2018.
- Hameroff, Stuart (2012). "How quantum brain biology can rescue conscious free will". Frontiers in Integrative Neuroscience. 6 (93). doi:10.3389/fnint.2012.00093.
- Hameroff, Stuart; Penrose, Roger (March 2014). "Reply to criticism of the 'Orch OR qubit' – 'Orchestrated objective reduction' is scientifically justified". Physics of Life Reviews. Elsevier. 11 (1): 94–100. Bibcode:2014PhLRv..11...94H. doi:10.1016/j.plrev.2013.11.013. Retrieved 17 March 2014.
- Penrose, Roger (2014). "On the Gravitization of Quantum Mechanics 1: Quantum State Reduction". Foundations of Physics. 44: 557–575. Bibcode:014FoPh...44..557P Check
|bibcode=length (help). doi:10.1007/s10701-013-9770-0. Retrieved 12 June 2016.
- McCulloch, Warren S.; Pitts, Walter (1943). "A logical calculus of the ideas immanent in nervous activity". The Bulletin of Mathematical Biophysics. 5 (4): 115–133. doi:10.1007/bf02478259.
- Hodgkin, Alan L.; Huxley, Andrew F. (1952). "A quantitative description of membrane current and its application to conduction and excitation in nerve". Journal of Physiology. 117 (4): 500–544. doi:10.1113/jphysiol.1952.sp004764. PMC 1392413. PMID 12991237.
- Chopra, Deepak (2014-03-18). "'Collision Course' in the Science of Consciousness: Grand Theories to Clash at Tucson Conference". The Huffington Post. United States: TheHuffingtonPost.com, Inc. Archived from the original on 18 March 2014. Retrieved 2014-03-18.
- Hameroff, Stuart; Penrose, Roger (March 2014). "Reply to seven commentaries on "Consciousness in the universe: Review of the 'Orch OR' theory"". Physics of Life Reviews. Elsevier. 11 (1): 104–112. Bibcode:2014PhLRv..11..104H. doi:10.1016/j.plrev.2013.11.014. Retrieved 16 March 2014.
- Natalie Wolchover (31 October 2013). "Physicists Eye Quantum-Gravity Interface". Quanta Magazine (Article). Simons Foundation. Retrieved 19 March 2014.
- Boolos, George, et al. 1990. An Open Peer Commentary on The Emperor's New Mind. Behavioral and Brain Sciences 13 (4) 655.
- Davis, Martin 1993. How subtle is Gödel's theorem? More on Roger Penrose. Behavioral and Brain Sciences, 16, 611–612. Online version at Davis' faculty page at http://cs.nyu.edu/cs/faculty/davism/
- Lewis, David K. 1969.Lucas against mechanism. Philosophy 44 231–233.
- Putnam, Hilary 1995. Review of Shadows of the Mind. In Bulletin of the American Mathematical Society 32, 370–373 (also see Putnam's less technical criticisms in his New York Times review)
- Tegmark, Max (April 2000). "Importance of quantum decoherence in brain processes". Phys. Rev. E. 61 (4): 4194–4206. arXiv:quant-ph/9907009. Bibcode:2000PhRvE..61.4194T. doi:10.1103/PhysRevE.61.4194. Retrieved 18 November 2012.
- McKemmish, L.K., Reimers, J.R., McKenzie, R.H., Mark, A.E., and Hush, N.S. (2009). "Penrose–Hameroff orchestrated objective-reduction proposal for human consciousness is not biologically feasible". Physical Review E. 80 (2): 021912–021916. Bibcode:2009PhRvE..80b1912M. doi:10.1103/PhysRevE.80.021912.
- Georgiev, D.D. (2007). "Falsifications of Hameroff–Penrose Orch OR model of consciousness and novel avenues for development of quantum mind theory". NeuroQuantology. 5 (1): 145–174. doi:10.14704/nq.2007.5.1.121.
- Koch, Christof; Hepp, Klaus (30 March 2006). "Quantum mechanics in the brain". Nature. 440 (7084): 611. Bibcode:2006Natur.440..611K. doi:10.1038/440611a. Retrieved 8 August 2013.
- Hepp, K. (27 September 2012). "Coherence and decoherence in the brain". J. Math. Phys. 53 (9): 095222. Bibcode:2012JMP....53i5222H. doi:10.1063/1.4752474. Retrieved 8 August 2013.
- "Discovery of Quantum Vibrations in "Microtubules" Inside Brain Neurons Corroborates Controversial 20-Year-Old Theory of Consciousness". elsevier.com (press release). Amsterdam: Elsevier. 16 January 2014. Retrieved 19 March 2014.
- Maurits van den Noort, Sabina Lim, Peggy Bosch (2016-10-28). "Towards a theory of everything: The observer's unconscious brain". Nature. 538: 36–37. Bibcode:2016Natur.538...36D. doi:10.1038/538036a. Retrieved 2016-04-11.
- Hofstadter 1979, pp. 476–477, Russell & Norvig 2003, p. 950, Turing 1950 under "The Argument from Mathematics" where he writes "although it is established that there are limitations to the powers of any particular machine, it has only been stated, without sort of proof, that no such limitations apply to the human intellect."
- Penrose, Roger (1989). The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics. Oxford University Press. p. 480. ISBN 0-19-851973-7.
- Penrose, Roger (1989). Shadows of the Mind: A Search for the Missing Science of Consciousness. Oxford University Press. p. 457. ISBN 0-19-853978-9.
- LaForte, Geoffrey, Patrick J. Hayes, and Kenneth M. Ford 1998.Why Gödel's Theorem Cannot Refute Computationalism. Artificial Intelligence, 104:265–286.
- Feferman, Solomon (1996). "Penrose's Gödelian argument". Psyche: An Interdisciplinary Journal of Research on Consciousness. 2: 21–32. CiteSeerX 10.1.1.130.7027.
- Krajewski, Stanislaw 2007. On Gödel's Theorem and Mechanism: Inconsistency or Unsoundness is Unavoidable in any Attempt to 'Out-Gödel' the Mechanist. Fundamenta Informaticae 81, 173–181. Reprinted in Topics in Logic, Philosophy and Foundations of Mathematics and Computer Science:In Recognition of Professor Andrzej Grzegorczyk (2008), p. 173
- "MindPapers: 6.1b. Godelian arguments". Consc.net. Retrieved 2014-07-28.
- "References for Criticisms of the Gödelian Argument". Users.ox.ac.uk. 1999-07-10. Retrieved 2014-07-28.
- Bringsjord, S. and Xiao, H. 2000. A Refutation of Penrose's Gödelian Case Against Artificial Intelligence. Journal of Experimental and Theoretical Artificial Intelligence 12: 307–329. The authors write that it is "generally agreed" that Penrose "failed to destroy the computational conception of mind."
- In an article at "Archived copy". Archived from the original on 2001-01-25. Retrieved 2010-10-22. L.J. Landau at the Mathematics Department of King's College London writes that "Penrose's argument, its basis and implications, is rejected by experts in the fields which it touches."
- Princeton Philosophy professor John Burgess writes in On the Outside Looking In: A Caution about Conservativeness (published in Kurt Gödel: Essays for his Centennial, with the following comments found on pp. 131–132) that "the consensus view of logicians today seems to be that the Lucas–Penrose argument is fallacious, though as I have said elsewhere, there is at least this much to be said for Lucas and Penrose, that logicians are not unanimously agreed as to where precisely the fallacy in their argument lies. There are at least three points at which the argument may be attacked."
- Dershowitz, Nachum 2005. The Four Sons of Penrose, in Proceedings of the Eleventh Conference on Logic for Programming, Artificial Intelligence, and Reasoning (LPAR; Jamaica), G. Sutcliffe and A. Voronkov, eds., Lecture Notes in Computer Science, vol. 3835, Springer-Verlag, Berlin, pp. 125–138.
- Marvin Minsky. "Conscious Machines." Machinery of Consciousness, Proceedings, National Research Council of Canada, 75th Anniversary Symposium on Science in Society, June 1991.
- Hameroff, S.R. & Watt, R.C. (1982). "Information processing in microtubules" (PDF). Journal of Theoretical Biology. 98 (4): 549–561. doi:10.1016/0022-5193(82)90137-0. PMID 6185798.
- Hameroff, S.R. (1987). Ultimate Computing. Elsevier. ISBN 0-444-70283-0. Archived from the original on 2005-04-06.
- Hameroff, Stuart (2008). "That's life! The geometry of π electron resonance clouds". In Abbott, D; Davies, P; Pati, A. Quantum aspects of life (PDF). World Scientific. pp. 403–434. Retrieved Jan 21, 2010.
- Roger Penrose & Stuart Hameroff (2011). "Consciousness in the Universe: Neuroscience, Quantum Space-Time Geometry and Orch OR Theory". Journal of Cosmology. 14.
- Reimers, Jeffrey R.; McKemmish, Laura K.; McKenzie, Ross H.; Mark, Alan E.; Hush, Noel S. (17 March 2009). "Weak, strong, and coherent regimes of Fröhlich condensation and their applications to terahertz medicine and quantum consciousness". PNAS. 106 (11): 4219–4224. Bibcode:2009PNAS..106.4219R. doi:10.1073/pnas.0806273106. PMC 2657444. PMID 19251667.
- Hameroff, S.R. (2006). "The entwined mysteries of anesthesia and consciousness". Anesthesiology. 105 (2): 400–412. doi:10.1097/00000542-200608000-00024. PMID 16871075.
- Hameroff, S. (2009). "The "conscious pilot"—dendritic synchrony moves through the brain to mediate consciousness". Journal of Biological Physics. 36 (1): 71–93. doi:10.1007/s10867-009-9148-x. PMC 2791805. PMID 19669425.
- Bennett, M.V.L. & Zukin, R.S. (2004). "Electrical Coupling and Neuronal Synchronization in the Mammalian Brain". Neuron. 41 (4): 495–511. doi:10.1016/S0896-6273(04)00043-1. PMID 14980200.
- Hameroff, S.R. (1998). "Quantum Computation In Brain Microtubules? The Penrose–Hameroff "Orch OR" model of consciousness". Philosophical Transactions of the Royal Society A. 356: 1869–1896. Bibcode:1998RSPTA.356.1869H. doi:10.1098/rsta.1998.0254.
- Anirban Bandyopadhyay (26 March 2013). "Multi-level memory-switching properties of a single brain microtubule". Applied Physics Letters. American Institute of Physics. 102 (12): 123701. Bibcode:2013ApPhL.102l3701S. doi:10.1063/1.4793995. Retrieved 16 March 2014.
- Anirban Bandyopadhyay (15 March 2013). "Atomic water channel controlling remarkable properties of a single brain microtubule: correlating single protein to its supramolecular assembly". Biosens Bioelectron. Elsevier. 47 (12): 141–8. doi:10.1016/j.bios.2013.02.050. PMID 23567633.
- "Discovery of quantum vibrations in microtubules inside brain neurons corroborates controversial 20-year-old theory of consciousness". KurzweilAI. 2014-01-16. Retrieved 2014-02-01.
- "Penrose, Hameroff & Bandyopadhyay, Lecture: Microtubules and the great debate about consciousness (Lezing: Microtubuli & het grote debat over het bewustzijn)". Brakke Grond. 2014-01-16. Retrieved 2014-02-01.
- "Discovery of quantum vibrations in 'microtubules' inside brain neurons supports controversial theory of consciousness". ScienceDaily. Jan 2014. Retrieved 2014-02-22.
- Ouellette, Jennifer (2 November 2016). "A New Spin on the Quantum Brain". Quanta Magazine. Retrieved 5 December 2018.
- Marshall, W., Simon, C., Penrose, R., and Bouwmeester, D. (2003). "Towards quantum superpositions of a mirror". Physical Review Letters. 91 (13): 130401. arXiv:quant-ph/0210001. Bibcode:2003PhRvL..91m0401M. doi:10.1103/PhysRevLett.91.130401. PMID 14525288.
- Reimers, Jeffrey; McKemmish, Laura; McKenziec, Ross; Markd, Alan; Hush, Noel. "The revised Penrose-Hameroff orchestrated objective-reduction proposal for human consciousness is not scientifically justified: Comment on "Consciousness in the universe: A review of the 'Orch OR' theory" by Hameroff and Penrose" (PDF). Physics of Life Reviews. 11 (2014): 101–103. Bibcode:2014PhLRv..11..101R. doi:10.1016/j.plrev.2013.11.003. Retrieved 24 Sep 2014.
- Villatoro, Francisco R. (June 17, 2015). "On the quantum theory of consciousness". Mapping Ignorance. University of the Basque Country. Retrieved August 18, 2018.
Hameroff's ideas in the hands of Penrose have developed almost to absurdity.
- Baars BJ, Edelman DB (2012). "Consciousness, biology and quantum hypotheses". Physics of Life Reviews. 9 (3): 285–294. doi:10.1016/j.plrev.2012.07.001.
- Georgiev, Danko D. (2017). Quantum Information and Consciousness: A Gentle Introduction. Boca Raton: CRC Press. p. 177. ISBN 9781138104488. OCLC 1003273264.
- Litt A, Eliasmith C, Kroon FW, Weinstein S, Thagard P (2006). "Is the brain a quantum computer?". Cognitive Science. 30 (3): 593–603. doi:10.1207/s15516709cog0000_59. PMID 21702826.
- Hagan, S., Hameroff, S., and Tuszyński, J. (2002). "Quantum Computation in Brain Microtubules? Decoherence and Biological Feasibility". Physical Review E. 65 (6): 061901. arXiv:quant-ph/0005025. Bibcode:2002PhRvE..65f1901H. doi:10.1103/PhysRevE.65.061901. Retrieved 16 March 2014.
- Hameroff, S. (2006). "Consciousness, Neurobiology and Quantum Mechanics". In Tuszynski, Jack. The Emerging Physics of Consciousness. Springer. pp. 193–253.
- Maurer PC, Kucsko G, Latta C, Jiang L, Yao NY, Bennett SD, Pastawski F, Hunger D, Chisholm N, Markham M, Twitchen DJ, Cirac JI, Lukin MD (2012). "Room-temperature quantum bit memory exceeding one second". Science. 336 (6086): 1283–1286. doi:10.1126/science.1220513.
- Baron, David. "Quantum computing, no cooling required | Harvard Gazette". News.harvard.edu. Retrieved 2014-07-28.
- Engel, G.S., Calhoun, T.R., Read, E.L., Ahn, T.-K., Mancal, T., Cheng, Y.-C., Blankenship, R.E., and Fleming, G.R. (2007). "Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems". Nature. 446 (7137): 782–786. Bibcode:2007Natur.446..782E. doi:10.1038/nature05678. PMID 17429397. Retrieved 17 March 2014.
- Craddock, Travis John Adrian; Friesen, Douglas; Mane, Jonathan; Hameroff, Stuart; Tuszynski, Jack (17 Sep 2014). "The feasibility of coherent energy transfer in microtubules". Journal of the Royal Society Interface. 11 (100): 1742–5662. arXiv:1405.3170. doi:10.1098/rsif.2014.0677. Retrieved 24 Sep 2014.
- Panitchayangkoon, Gitt; Dugan Hayes; Kelly A. Fransted; Justin R. Caram; Elad Harel; Jianzhong Wen; Robert E. Blankenship; Gregory S. Engel (6 July 2010). "Long-lived quantum coherence in photosynthetic complexes at physiological temperature". Proceedings of the National Academy of Sciences. 107 (28): 12766–12770. arXiv:1001.5108. Bibcode:2010PNAS..10712766P. doi:10.1073/pnas.1005484107. PMC 2919932. PMID 20615985.
- Georgiev, D. D. (2009). "Remarks on the number of tubulin dimers per neuron and implications for Hameroff-Penrose Orch OR". NeuroQuantology. 7 (4): 677–679. doi:10.14704/nq.2009.7.4.261.
- Yu W, Baas PW (1994). "Changes in microtubule number and length during axon differentiation". Journal of Neuroscience. 14 (5): 2818–2829. doi:10.1523/jneurosci.14-05-02818.1994.
- Kikkawa, M., Ishikawa, T., Nakata, T., Wakabayashi, T., Hirokawa, N. (1994). "Direct visualization of the microtubule lattice seam both in vitro and in vivo". Journal of Cell Biology. 127 (6): 1965–1971. doi:10.1083/jcb.127.6.1965. PMC 2120284. PMID 7806574.
- Kikkawa, M., Metlagel, Z. (2006). "A molecular "zipper" for microtubules". Cell. 127 (7): 1302–1304. doi:10.1016/j.cell.2006.12.009. PMID 17190594.
- F. J. Binmöller & C. M. Müller (1992). "Postnatal development of dye-coupling among astrocytes in rat visual cortex". Glia. 6 (2): 127–137. doi:10.1002/glia.440060207. PMID 1328051.
- Fróes MM, Correia AH, Garcia-Abreu J, Spray DC, Campos de Carvalho AC, Neto VM (1999). "Gap-junctional coupling between neurons and astrocytes in primary central nervous system cultures". Proceedings of the National Academy of Sciences of the United States of America. 96 (13): 7541–7546. doi:10.1073/pnas.96.13.7541. PMC 22122. PMID 10377451.
- Hameroff SR (2001). "Consciousness, the brain, and spacetime geometry". Annals of the New York Academy of Sciences. 929 (1): 74–104. doi:10.1111/j.1749-6632.2001.tb05709.x. PMID 11349432.
- De Zeeuw, C.I., Hertzberg, E.L., Mugnaini, E. (1995). "The dendritic lamellar body: A new neuronal organelle putatively associated with dendrodentritic gap junctions". Journal of Neuroscience. 15 (2): 1587–1604. PMID 7869120.
- Subrata Ghosh; Satyajit Sahu; Anirban Bandyopadhyaya (2013). "Evidence of massive global synchronization and the consciousness: Comment on "Consciousness in the universe: A review of the 'Orch OR' theory" by Hameroff and Penrose". Physics of Life Reviews. 11: 83–84. Bibcode:2014PhLRv..11...83G. doi:10.1016/j.plrev.2013.10.007.
- Georgiev, D. (2011). "Photons do collapse in the retina not in the brain cortex: Evidence from visual illusions". Neuroquantology. 9 (2): 206–231. arXiv:quant-ph/0208053. Bibcode:2002quant.ph..8053G. doi:10.14704/nq.2011.9.2.403.
- Khoshbin-e-Khoshnazar, M.R. (2007). "Achills heels of the Orch Or model". NuroQuantology. 5 (1): 182–185. doi:10.14704/nq.2007.5.1.123.
- Friedrich Beck; John C. Eccles (1992). "Quantum aspects of brain activity and the role of consciousness" (PDF). Proc. Natl. Acad. Sci. U.S.A. 89 (23): 11357–11361. doi:10.1073/pnas.89.23.11357. PMC 50549. PMID 1333607.
- Friedrich Beck (1996). "Can quantum processes control synaptic emission?". International Journal of Neural Systems. 7 (4): 343–353. doi:10.1142/S0129065796000300. PMID 8968823.
- Friedrich Beck; John C. Eccles (1998). "Quantum processes in the brain: A scientific basis of consciousness". Cognitive Studies: Bulletin of the Japanese Cognitive Science Society. 5 (2): 95–109. doi:10.11225/jcss.5.2_95.
- Danaylov, Nikola, ed. (12 Sep 2013). Stuart Hameroff on Singularity 1 on 1: Consciousness is More than Computation!. Singularity Weblog. Event occurs at 00:30:59. Retrieved 25 March 2014.
They [the Wikipedia article] talk about ... some fairly minor things, all of which are wrong! ... I dispute Wikipedia :-)