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Quantum brain biology complements neuronal assembly approaches to consciousness
Available online at www.sciencedirect.com
Physics of Life Reviews 9 (2012) 303–305 www.elsevier.com/locate/plrev
Comment
Quantum brain biology complements neuronal assembly approaches to consciousness Comment on “Consciousness, biology and quantum hypotheses” by Baars and Edelman Stuart Hameroff Departments of Anesthesiology and Psychology, Center for Consciousness Studies, The University of Arizona, 1501 N Campbell Ave, Tucson, AZ 85724, USA Received 15 June 2012; accepted 6 July 2012 Available online 11 July 2012 Communicated by L. Perlovsky
Keywords: Consciousness; Microtubules; Quantum computing; Penrose–Hameroff Orch OR; Tubulin; Gap junctions
Baars and Edelman (B&E) [1] portray the neural correlate of consciousness (NCC) as higher order dynamics in neuronal assemblies in the brain’s cortico-thalamic system, and criticize quantum approaches to consciousness, particularly the Penrose–Hameroff ‘Orch OR’ model of quantum computation in microtubules inside brain neurons [2–4]. The B&E approach is erroneous and inadequate, but if modified, can be complemented by deeper order dynamics within neurons, e.g. Orch OR, to give a clearer picture of the NCC. B&E neuronal assemblies. B&E argue for oscillating assemblies of cortico-thalamic neurons driven by sensory inputs and connected by chemical synapses as the NCC. But their view is problematic: 1. In addition to sensory-driven mental states, ‘default-mode’ networks generate internal states, e.g. mind-wandering [5]. 2. Consciousness can occur in limbic, brainstem and other areas, not just cortex and thalamus [6]. 3. Olfaction and ‘locked-in syndromes’ illustrate consciousness without thalamic activity [7]. 4. Neuronal assemblies connected by chemical synapses don’t account for long-range gamma synchrony; gap junction electrical synapses are required [8]. 5. B&E describe nested phase coupling in EEG frequency ranges, and ‘small world’ network geometry, but fail to consider implications for scaleinvariant (‘fractal-like’, ‘1/f ’) dynamics and structure [9] (which may extend to deeper order quantum processes in microtubules). A modified type of assembly can meet these constraints and act as the NCC. Synchronized webs of neurons (and glia) connected by dendritic gap junctions form transient syncytia, ‘dendritic webs’. As gap junctions open and close, such webs can literally move through the brain as the NCC (housing quantum processes in microtubules) [8,10]. DOI of original article: http://dx.doi.org/10.1016/j.plrev.2012.07.001. E-mail address: [email protected]. 1571-0645/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.plrev.2012.07.002
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S. Hameroff / Physics of Life Reviews 9 (2012) 303–305
B&E’s main criticism of Orch OR is: What’s so special about brain microtubules? Microtubules (‘MTs’) are major components of the cell cytoskeleton, and, as B&E state, occur in all animal and plant cells. Why then, B&E imply, does consciousness not occur in your pancreas, buttock, or a rutabaga? Orch OR, the only theory to specify a mechanism for conscious moments, can occur in brain MTs, and not elsewhere, because: Unique networks. In Orch OR, MT quantum computations occur in neuronal dendrites and cell bodies/soma during integration phases in integrate-and-fire neurons [8]. Dendritic/somatic MTs are uniquely arrayed. In axons, and all other animal and plant cells, MTs are radial, with the same polarity, extending outward without interruption from centrosome to the cell periphery. However dendritic/somatic MTs are short, interrupted and arrayed with mixed polarity in local recursive networks, interconnected by MT-associated proteins (‘MAPs’) [11]. These unique MT–MAP networks apparently correlate with consciousness. Stability. MTs are self-assembling polymers of the protein tubulin. Non-neuronal cells divide repeatedly and recycle tubulins for mitotic spindle MTs. But neurons don’t divide, their MTs remaining polymerized for the life of the cell, suitable for information encoding, memory and consciousness [12]. Number of tubulins. In Orch OR, MT tubulins exist as information states, e.g. bits of 1 or 0, and also as superpositioned quantum bits, or qubits of both 1 and 0. Entangled qubits interact in neuronal integration until objective threshold for state reduction is reached (Penrose ‘objective reduction’, ‘OR’) by E = h¯ /t , where E is the magnitude (gravitational self-energy) of the superposition, e.g. the number of tubulins (E is also proportional to intensity of experience). h¯ is Planck’s constant (over 2π ), and t the time at which OR conscious moments occur. Each OR selects MT output states which govern axonal firings and regulate synapses. Synaptic inputs ‘orchestrate’ these MT quantum computations, hence ‘orchestrated objective reduction’, ‘Orch OR’ [2–4]. MT quantum states entangle with MTs in other neurons through dendritic gap junctions. For t = 25 msec (40 Hz gamma synchrony) by E = h/t, E is ∼10 billion tubulins (∼100,000 neurons). Thus for brief, useful conscious ¯ moments, large numbers of entangled MTs in many gap junction-connected neurons are required. This can only occur in the brain. A skin cell, or rutabaga could conceivably have a very weak conscious moment once per month or so, assuming decoherence could be avoided. Some other issues raised by B&E: Conscious versus non-conscious processes. Cognition within neurons in which Orch OR occurs by E = h¯ /t is accompanied by conscious experience and volition. Cognition in neurons in which Orch OR does not occur is non-conscious, or ‘auto-pilot’ [8]. Also, anesthetic gases reversibly erase consciousness, sparing non-conscious brain processes, acting strictly by quantum London forces [13]. Quantum observer. B&E criticize the von Neumann/Wigner observer interpretation in which consciousness reduces/collapses the wave function. This puts consciousness outside science. In Orch OR, consciousness IS collapse, a self-organizing process on the edge between quantum and classical realms. Orch OR places consciousness in science, and is completely opposite to the observer effect. Binocular rivalry. B&E discuss binocular rivalry and bistable illusions (e.g. ‘Necker cube’) in which consciousness switches back and forth between alternative percepts. In Orch OR, this is superposition (E) of both percepts which reduce/collapse by E = h/t ¯ to one or the other at intervals of time t . Bird navigation. B&E state: “. . . migratory birds. . . require sophisticated brains to navigate. . . . No special explanatory mechanisms need to be invoked to explain. . . navigation. . . .” This is false. The ‘avian compass’ in brains of birds utilizes quantum superposition and entanglement to track the earth’s magnetic field [14]. Conclusion. As Shakespeare said, B&E “doth protest too much”, clouding their weakness by discrediting alternatives. But quantum brain biology can be complementary to neuronal assembly approaches, e.g. consciousness occurring by Orch OR within gap junction-defined synchronized zones. As Bob Dylan said: “Don’t criticize what you can’t understand. . . For the times, they are a-changin”.
S. Hameroff / Physics of Life Reviews 9 (2012) 303–305
305
References [1] Baars BJ, Edelman DB. Consciousness, biology and quantum hypotheses. Phys Life Rev 2012;9(3):285–94 [this issue]. [2] Penrose R, Hameroff S. Consciousness in the universe: neuroscience, quantum space–time geometry and Orch OR theory. J Cosmology 2011;14. http://www.quantumconsciousness.org/Cosmology160.html. [3] Hameroff S, Penrose R. Conscious events as orchestrated space–time selections. J Consciousness Studies 1996;3(1):36–53. [4] Hameroff S. Quantum computation in brain microtubules? The Penrose–Hameroff ‘Orch OR’ model of consciousness. Philos Trans R Soc Lond A 1998;356:1869–96. [5] Mason MF, Norton MI, Van Horn JD, Wegner DM, Gratfton ST, Macrae CN. Wandering minds: the default network and stimulus-independent thought. Science 2007;315(5810):393–5. [6] Parvizi J, Damasio A. Consciousness and the brainstem. Cognition 2001;79(1–2):135–60. [7] Laureys S, Pellas F, Van Eeckhout P, Ghorbel S, Schnakers C, Perrin F, et al. The locked-in syndrome: what is it like to be conscious but paralyzed and voiceless? Prog Brain Res 2005;150:495–511. [8] Hameroff S. The “conscious pilot” – dendritic synchrony moves through the brain to mediate consciousness. J Biol Phys 2010;36(1):71–93. [9] He BJ, Zemper JM, Snyder AZ, Raichle ME. The temporal structures and functional significance of scale-free brain activity. Neuron 2010;66(3):353–69. [10] Ebner M, Hameroff S. Lateral information processing by spiking neurons: a theoretical model of the neural correlate of consciousness. Comput Intell Neurosci 2011. http://dx.doi.org/10.1155/2011/247879. [11] Stone MC, Roegiers F, Rolls MM. Microtubules have opposite orientation in axons and dendrites of Drosophila neurons. Mol Biol Cell 2008;19(10):4122–9. [12] Craddock TJA, Tuszynski JA, Hameroff S. Cytoskeletal signaling: is memory encoded in microtubule lattices by CaMKII phosphorylation? PLoS Comput Biol 2012;8(3):e1002421. http://dx.doi.org/10.1371/journal.pcbi.1002421. [13] Hameroff S. The entwined mysteries of anesthesia and consciousness. Anesthesiology 2006;105:400–12. [14] Gauger EM, Rieper E, Morton JJL, Benjamin SC, Vedral V. Sustained quantum coherence and entanglement in the avian compass. Phys Rev Lett 2011;106:040503.
Physics of Life Reviews 9 (2012) 303–305 www.elsevier.com/locate/plrev
Comment
Quantum brain biology complements neuronal assembly approaches to consciousness Comment on “Consciousness, biology and quantum hypotheses” by Baars and Edelman Stuart Hameroff Departments of Anesthesiology and Psychology, Center for Consciousness Studies, The University of Arizona, 1501 N Campbell Ave, Tucson, AZ 85724, USA Received 15 June 2012; accepted 6 July 2012 Available online 11 July 2012 Communicated by L. Perlovsky
Keywords: Consciousness; Microtubules; Quantum computing; Penrose–Hameroff Orch OR; Tubulin; Gap junctions
Baars and Edelman (B&E) [1] portray the neural correlate of consciousness (NCC) as higher order dynamics in neuronal assemblies in the brain’s cortico-thalamic system, and criticize quantum approaches to consciousness, particularly the Penrose–Hameroff ‘Orch OR’ model of quantum computation in microtubules inside brain neurons [2–4]. The B&E approach is erroneous and inadequate, but if modified, can be complemented by deeper order dynamics within neurons, e.g. Orch OR, to give a clearer picture of the NCC. B&E neuronal assemblies. B&E argue for oscillating assemblies of cortico-thalamic neurons driven by sensory inputs and connected by chemical synapses as the NCC. But their view is problematic: 1. In addition to sensory-driven mental states, ‘default-mode’ networks generate internal states, e.g. mind-wandering [5]. 2. Consciousness can occur in limbic, brainstem and other areas, not just cortex and thalamus [6]. 3. Olfaction and ‘locked-in syndromes’ illustrate consciousness without thalamic activity [7]. 4. Neuronal assemblies connected by chemical synapses don’t account for long-range gamma synchrony; gap junction electrical synapses are required [8]. 5. B&E describe nested phase coupling in EEG frequency ranges, and ‘small world’ network geometry, but fail to consider implications for scaleinvariant (‘fractal-like’, ‘1/f ’) dynamics and structure [9] (which may extend to deeper order quantum processes in microtubules). A modified type of assembly can meet these constraints and act as the NCC. Synchronized webs of neurons (and glia) connected by dendritic gap junctions form transient syncytia, ‘dendritic webs’. As gap junctions open and close, such webs can literally move through the brain as the NCC (housing quantum processes in microtubules) [8,10]. DOI of original article: http://dx.doi.org/10.1016/j.plrev.2012.07.001. E-mail address: [email protected]. 1571-0645/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.plrev.2012.07.002
304
S. Hameroff / Physics of Life Reviews 9 (2012) 303–305
B&E’s main criticism of Orch OR is: What’s so special about brain microtubules? Microtubules (‘MTs’) are major components of the cell cytoskeleton, and, as B&E state, occur in all animal and plant cells. Why then, B&E imply, does consciousness not occur in your pancreas, buttock, or a rutabaga? Orch OR, the only theory to specify a mechanism for conscious moments, can occur in brain MTs, and not elsewhere, because: Unique networks. In Orch OR, MT quantum computations occur in neuronal dendrites and cell bodies/soma during integration phases in integrate-and-fire neurons [8]. Dendritic/somatic MTs are uniquely arrayed. In axons, and all other animal and plant cells, MTs are radial, with the same polarity, extending outward without interruption from centrosome to the cell periphery. However dendritic/somatic MTs are short, interrupted and arrayed with mixed polarity in local recursive networks, interconnected by MT-associated proteins (‘MAPs’) [11]. These unique MT–MAP networks apparently correlate with consciousness. Stability. MTs are self-assembling polymers of the protein tubulin. Non-neuronal cells divide repeatedly and recycle tubulins for mitotic spindle MTs. But neurons don’t divide, their MTs remaining polymerized for the life of the cell, suitable for information encoding, memory and consciousness [12]. Number of tubulins. In Orch OR, MT tubulins exist as information states, e.g. bits of 1 or 0, and also as superpositioned quantum bits, or qubits of both 1 and 0. Entangled qubits interact in neuronal integration until objective threshold for state reduction is reached (Penrose ‘objective reduction’, ‘OR’) by E = h¯ /t , where E is the magnitude (gravitational self-energy) of the superposition, e.g. the number of tubulins (E is also proportional to intensity of experience). h¯ is Planck’s constant (over 2π ), and t the time at which OR conscious moments occur. Each OR selects MT output states which govern axonal firings and regulate synapses. Synaptic inputs ‘orchestrate’ these MT quantum computations, hence ‘orchestrated objective reduction’, ‘Orch OR’ [2–4]. MT quantum states entangle with MTs in other neurons through dendritic gap junctions. For t = 25 msec (40 Hz gamma synchrony) by E = h/t, E is ∼10 billion tubulins (∼100,000 neurons). Thus for brief, useful conscious ¯ moments, large numbers of entangled MTs in many gap junction-connected neurons are required. This can only occur in the brain. A skin cell, or rutabaga could conceivably have a very weak conscious moment once per month or so, assuming decoherence could be avoided. Some other issues raised by B&E: Conscious versus non-conscious processes. Cognition within neurons in which Orch OR occurs by E = h¯ /t is accompanied by conscious experience and volition. Cognition in neurons in which Orch OR does not occur is non-conscious, or ‘auto-pilot’ [8]. Also, anesthetic gases reversibly erase consciousness, sparing non-conscious brain processes, acting strictly by quantum London forces [13]. Quantum observer. B&E criticize the von Neumann/Wigner observer interpretation in which consciousness reduces/collapses the wave function. This puts consciousness outside science. In Orch OR, consciousness IS collapse, a self-organizing process on the edge between quantum and classical realms. Orch OR places consciousness in science, and is completely opposite to the observer effect. Binocular rivalry. B&E discuss binocular rivalry and bistable illusions (e.g. ‘Necker cube’) in which consciousness switches back and forth between alternative percepts. In Orch OR, this is superposition (E) of both percepts which reduce/collapse by E = h/t ¯ to one or the other at intervals of time t . Bird navigation. B&E state: “. . . migratory birds. . . require sophisticated brains to navigate. . . . No special explanatory mechanisms need to be invoked to explain. . . navigation. . . .” This is false. The ‘avian compass’ in brains of birds utilizes quantum superposition and entanglement to track the earth’s magnetic field [14]. Conclusion. As Shakespeare said, B&E “doth protest too much”, clouding their weakness by discrediting alternatives. But quantum brain biology can be complementary to neuronal assembly approaches, e.g. consciousness occurring by Orch OR within gap junction-defined synchronized zones. As Bob Dylan said: “Don’t criticize what you can’t understand. . . For the times, they are a-changin”.
S. Hameroff / Physics of Life Reviews 9 (2012) 303–305
305
References [1] Baars BJ, Edelman DB. Consciousness, biology and quantum hypotheses. Phys Life Rev 2012;9(3):285–94 [this issue]. [2] Penrose R, Hameroff S. Consciousness in the universe: neuroscience, quantum space–time geometry and Orch OR theory. J Cosmology 2011;14. http://www.quantumconsciousness.org/Cosmology160.html. [3] Hameroff S, Penrose R. Conscious events as orchestrated space–time selections. J Consciousness Studies 1996;3(1):36–53. [4] Hameroff S. Quantum computation in brain microtubules? The Penrose–Hameroff ‘Orch OR’ model of consciousness. Philos Trans R Soc Lond A 1998;356:1869–96. [5] Mason MF, Norton MI, Van Horn JD, Wegner DM, Gratfton ST, Macrae CN. Wandering minds: the default network and stimulus-independent thought. Science 2007;315(5810):393–5. [6] Parvizi J, Damasio A. Consciousness and the brainstem. Cognition 2001;79(1–2):135–60. [7] Laureys S, Pellas F, Van Eeckhout P, Ghorbel S, Schnakers C, Perrin F, et al. The locked-in syndrome: what is it like to be conscious but paralyzed and voiceless? Prog Brain Res 2005;150:495–511. [8] Hameroff S. The “conscious pilot” – dendritic synchrony moves through the brain to mediate consciousness. J Biol Phys 2010;36(1):71–93. [9] He BJ, Zemper JM, Snyder AZ, Raichle ME. The temporal structures and functional significance of scale-free brain activity. Neuron 2010;66(3):353–69. [10] Ebner M, Hameroff S. Lateral information processing by spiking neurons: a theoretical model of the neural correlate of consciousness. Comput Intell Neurosci 2011. http://dx.doi.org/10.1155/2011/247879. [11] Stone MC, Roegiers F, Rolls MM. Microtubules have opposite orientation in axons and dendrites of Drosophila neurons. Mol Biol Cell 2008;19(10):4122–9. [12] Craddock TJA, Tuszynski JA, Hameroff S. Cytoskeletal signaling: is memory encoded in microtubule lattices by CaMKII phosphorylation? PLoS Comput Biol 2012;8(3):e1002421. http://dx.doi.org/10.1371/journal.pcbi.1002421. [13] Hameroff S. The entwined mysteries of anesthesia and consciousness. Anesthesiology 2006;105:400–12. [14] Gauger EM, Rieper E, Morton JJL, Benjamin SC, Vedral V. Sustained quantum coherence and entanglement in the avian compass. Phys Rev Lett 2011;106:040503.