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Penrose & Hameroff 7Further papers by Stuart Hameroff and others plus Pokorny paper on the cytoskeleton. 1.) The Orch OR Model - Stuart Hameroff 2.) The Orch OR Theory - Stuart Hameroff 3.) Stuart Hameroff - in Annals of the New York Academy of Sciences 4.) Quest for Consciousness - Stuart Hameroff reviews Christof Koch's book and Hameroff and Koch debate related matters. 5.) Quantum computation in brain microtubules? The Penrose-Hameroff Orch OR model of consciousness - Stuart Hameroff 6.) Conscious events as orchestrated spacetime selection - Stuart Hameroff & Roger Penrose 7.) Quantum computation in brain microtubules - in Philosophical Transaction of the Royal Society (1998) - Stuart Hameroff 8.) Consciousness, the brain and spacetime geometry - Stuart Hameroff 9.) Review of Penrose's 'The Large, the Small and the Human Brain by Brian Josephson 10.) Inflationary theory and the early universe - from Roger Penrose's 'Road to Reality' 11.) Dendritic synchrony moves through the brain to mediate consciousness - Stuart Hameroff 12.) Conditions for coherent vibration in the cytoskeleton - J. Pokorny - Discusses Frohlich ideas on energy condensation and coherence in organic matter. 1.) The Orch OR Model Stuart Hameroff & Roger Penrose Proteins are versatile macromolecules that perform a variety of functions by changing their conformation. This is important for a wide variety of functions such as muscle movement, opening and closing of ion channels in the cell membrane, and in fact most of life is organised by the conformation of proteins. Proteins are composed of hundreds of amino-acids. The main driver in the folding or conformation of protein is a non-polar group of amino-acids acting in hydrophobic pockets. Hydrophobic pockets may be critical to the functioning of protein. Anaesthetic gases exert effects in hydrophobic pockets by means of van der Waals forces. Protein is only marginally stable and conformation is a delicate balance between different forces. The timescale of conformation can be up to a nanosecond. Dipole to dipole forces are known as van der Waals forces. They can be permanent to permanent dipole, permanent to induced dipole or induced to induced. These last are called London or London dispersion forces and are the weakest type of Van der Waals force. They are 40x weaker than the hydrogen bonds. The London forces arise as a result of instantaneous dipoles in electrically neutral areas and they may couple to zero point fluctuations in the vacuum. It is also suggested that proteins may utilise superpositions of possible conformations. An experiment by Roitberg et al tended to confirm the existence of superpositions in protein. The interiors of living cells are organised by the cytoskeleton. They govern a number of functions including movement, maintenance of functions, extension of axons and dendrites, the formation of synapses and the regulation of synaptic strength. More recent signalling has been detected within the cytoskeleton. Proteins called fodrin and ankryn link the cytoskeleton to the cell membrane. Microtubules and the rest of the cytoskeleton are embedded in the cytoplasm. This can switch periodically between being a liquid and a gel and this may help to shield the microtubules. The MAPs are seen as setting the proababilities for the outcome of the quantum computation. There is a high concentration of gap junctions in the cortex and the thalamus. Appendix 2 of this article outlines 20 ways om which the Penrose/Hameroff model could be tested. Nineteen of these refer to properties of the brain and one to a test of Penrose's objective reduction proposal, which is stated to be in preparation. The article envisages that conformational states of tubulin in microtubules are coupled to internal quantum events within microtubules, and that these quantum events interact with other tubulins. It is also envisaged that macroscopic quantum coherence accounts for the binding of conscious experience into a unified whole. Penrose's hypothetical objective reduction (OR) supposes a spontaneous collapse of the wave function, when two possible space time geometries within a quantum superposition become separated by more than the Planck length. In Penrose's theory, the objective collapse is not random and it leads to a particular conformation of protein. Each objective collapse of the wave function in the microtubules is seen as a 'now' and instant of consciousness and an instant of psychological time, as opposed to the static time of relativity theory. The microtubules are also influenced by MAP (microtubule associated proteins) attachments, which connect to the cell membrane and the synapses. This is referred to as orchestratation, the ORCH of the ORCH OR model, which stands for orchestrated objective reduction. Theoretical modelling suggests that tubulins can interact with their neighbours to process information. Vassiler et al have demonstrated signal transmission along tubulin chains. Penrose suggets that objective reduction could be non-computable and a point of access to fundamental space-time geometry, the fundamental lvel of the universe. Physicists, Geroch and Hartle have provided some tentative support for the non-computability of four dimensional space time, by showing that there is no computable model for superpositions of space-time in the four dimensions of Einstein's relativity. In Penrose's theory, non-computability is only generated by self collapse as a result of quantum superpositions becoming separated by more than the Planck length, not by collapse caused by interaction with the environment or by measurements. Orch OR is thus seen as the only possible source of the non-computability, which Penrose believes to be necessary for some aspects of human understanding. Cells including neurons are organised by the cytoskeleton, which is formed out of tubulin, a protein polymer. It is self-organising and dynamic. Tubulin comes in 8nm long dimers, comprising slightly different 4nm long monomers. Microtubule associated proteins (MAPs) link the microtubules into networks. The microtubules are formed as an hexagonal lattice of tubulins, twisted so that tubulins have slightly different neighbour relationships. They are formed in helical rows of three, five and eight rows. Microtubules can be seen as orientated assemblies of dipoles capable of piezo and ferro electric behaviour, with energy supplied via tubulin bound GTP. Microtubules and MAPs determine the cell or neurons form and function. Long Term Potentiation (LTP), changes in synapses related to learning and memory, and regulation of synapses appears to be related to the MAPs. Brain damage due to loss of oxygen is also correlated to damage to microtubules and there is a further correlation with Alzheimers. Microtubules have strong ability to sustain a voltage gradient. This led Frohlich to suggest that there could be a quantum level dipole oscillation if energy was supplied. In the presence of biochemical energy, Frohlich thought that Bose-Einstein condensates could arise. There is suggestion that there is a ‘clock’ or timing mechanism to govern the position of the subunits that govern the processing of information. Jibu et al modelled the ordering of water molecules and the quantised electromagnetic field in the microtubule (MT) core, and predicted super-radiance, that is disordered energy being converted into coherent photons in the core of the MT. In the model this happens quicker than thermal decoherence can work in the opposite direction. 2.) The Orch OR Theory Stuart Hameroff Cell assembles are large enough to be individually conscious according to Hameroff’s calculations. The quantum computing of the tubulins is equated with unconscious processing by contrast with the Bose-Einstein condensate in the hollow core of the microtubule. In processing, Reduction of the wave function leads on to selection of a new set of tubulins. The processing in the tubulins in suggested to regulate the synapses. Penrose believes that the quantum wave reduction is a real event in physics. He thinks that non-computability in the brain is linked to non-computability in spacetime. He thinks that at least some conscious states in the brain cannot be derived from one another by algorithms. In this way, they are different in kind from the processing of computers, which is wholly governed by algorithms. Non-computability does not by itself give one consciousness, but it may be a step towards it. Objective reduction of the wave function may be common in the universe, but individual reductions are not relevant for the processing of consciousness. The reduction needs to be on a macroscopic scale to be relevant. In the brain there is proposed to be a cascade of ORs across different microtubules and different neurons, extending to a whole assembly of neurons, to produce the perceived ‘stream of consciousness’. The brain ORs are described as ‘orchestrated' ORs because they are orchestrated by the MAPs. Quantum superpositions represent many possible states with complex number weighted values, which, when the wave function collapses reduce to a single eigenstate. The result is random but can be weighted according to probability. Schrödinger, Heisenberg, Dirac and von Neumann all considered the possibility that superpositions could continue indefinitely up to macroscopic size. Conscious observation was sometimes called in to explain the collapse of these superpositions, but the possibility of an unobserved superposition remained. Penrose looks for an objective reduction (OR) to collapse the wave function, when the separation of different possible spacetime geometries exceeds the Planck length. Any attempt to persist with spacetime separation brings relativity and quantum theory into conflict. Several other physicists apart from Penrose have attempted to develop objective reduction theories, while Everett and Wheeler have tried to deal with the problem through the many worlds theory. Microtubules are seen as the most plausible candidates to support coherent quantum macroscopic activity in the brain, but clathrins and vesicular grids in the synaptic area and neural membrane proteins are also considered to be possible sites. Microtubules possess a range of features that make them suitable for a combination of quantum coherence and information processing. They are widespread and common throughout the brain, they have functional effects, a periodic structure, a possible ability to be transiently isolated, and they contain a hollow core that could conceivably act as a wave guide. A number of features appear to point to the ability of microtubules to screen quantum coherence including the hollow core, internal hydrophobic pockets, ordered water close to the microtubules and the sol/gel fluctuation in the cytoplasm. The article quotes a further experiment appearing to show quantum coherence in biological tissue. An experiment by Walleczek showed that biochemical radical pairs could retain the correlation of their quantum spin. The article further draws on the experience of meditators, who have reported a flickering in their experience of reality, in line with the suggestion that consciousness is a series of ‘now’ wave function collapses that only appear to be a stream of consciousness. Quantum computation has been shown to have a number of applications beyond those that can be achieved by a classical computer. Reserach is being conducted into the building of quantum computers, involving small entities such as trapped ions, or electron or nuclear spins. The main problem is decoherence. Conventional theories of consciousness assume that consciousness emerges from a process analogous to a classical computer, presumed to exist in the human brain. The main flaws of the conventional theory is the apparent inability to account for the subjective experience of consciousness as distinct from processing and responding to information, and the inability to explain the difference between the conscious and unconscious processing known to exist within the brain, given an apparent lack of differences in electrophysiological activity across the brain. The problem so far as the the brain and quantum computing is concerned is decoherence, since quantum computing requires either very low temperatures or energy pumping. At the same time as preserving coherence the quantum computer needs to communicate with the external environment to produce an output. In the Penrose/Hameroff model there is a crucial difference between quantum computers as such and the particular form of quantum computing involved in consciousness. This has been overlooked by some commentators. Presently planned quantum computers would have their wave functions collapse as a result of involvement with the environment, and this would definitely not involve non-computability. It is much more difficult to achieve objective reduction which is what is required for consciousness in this model. Furthermore the planned computers act only on small entities such as ions rather than macroscopic quantum entities that are felt to be relevant to consciousness. It is, however, suggested that the model does in principle open the door to the building of conscious quantum computers/robots, but this would probably be a long time in the future. 3.) Stuart Hameroff - in Annals of the New York Academy of Sciences There are two main types of neuronal circuits. The first is the relay of sensory information from the thalamus to the cortex, with amino-acid based neurotransmitters, such as glutamate acting on cortical dendrites. The second involves projections from the basal forebrain and midbrain, and which release acetylcholine and monoamines on a more widespread basis. It is suggested that the latter provide an attentional focus onto parts of the sensory input from the thalamus. Hameroff states that the synchronisation of brainwaves including the 40Hz gamma oscillation that is sometimes seen as a correlate of consciousness is performed by the gap junctions. Gap junctions are no known to be more widespread in the brain than was previously thought. With the tubulins that comprise the building blocks of microtubules, three dimensional analysis shows that they contain large non-polar hydrophobic pockets. These could use van der Waals forces to govern the movement of protein. Recently there has also been evidence of communication within the cytoskeleton. Actin gelation leads to the ordering of water in the cells. The interiors of neurons alternate between a liquid and a gel state. The gel is caused by polymerisation of the cytoskeletal protein actin. This oscillation can be in the 40Hz range and correlates with the release of neurotransmitters. But even in its liquid phase, the water in cells is significantly ordered, and can be regarded as active rather than inert. Studies indicate several layers of ordered water on cytoskeletal surfaces. There is also claimed to be scope for a Debye layer with one layer of charged ions attracting another layer of oppositely charged ions. The helical structure of the microtubules repeats in Fibonacci numbers, 5, 8, 13, 21 etc. and these define the point of MAP attachments to the microtubules. 4.) Quest for Consciousness Christoff Koch - review of Koch's book by Stuart Hameroff and debate between Koch and Hameroff Hameroff says that Koch's book acknowledges that there is a problem as to how qualia arises from the brain. However, he feels that the book somewhat sidesteps this central issue by concentrating on neural correlates of consciousness. As elsewhere, Hameroff expresses puzzlement as to the rapid adoption and equally rapid subsequent dropping of the 40 Hz or gamma oscillation by Crick and Koch in the 1990s. He surmises that this may be related to the discovery that synchronisation was with dendrites rather than axonal spiking, seen as the only area relevant to consciousness. Hameroff also criticises Koch's dismissive attitude to the linking of cortical interneurons by gap junctions. He states that dozens of papers show that interneurons linked by gap junctions drive the 40 Hz oscillation. He further reminds us that the 40 Hz oscillation is a correlate of consciousness which means that the interneuron/gap junction link is itself a correlate of consciousness. In his reply to Hameroff’s criticisms, Koch moves on to discuss the question of the laboratory mice that were bred not to have one of the Connexin family of proteins called Cx36. This is one of the proteins that constitute the gap junctions existing between some neurons in the brain. Koch states that in mice bred without Cx36, the 40Hz gamma oscillations persist, albeit at a reduced amplitude. There are some deficits in the behaviour of the mice, but they are not substantially different from normal mice. Koch and others have seen this as a knock out blow for the role given to gap junctions. In reply to this, Hameroff argues that the importance given to the deficit in Cx36 has been greatly exaggerated. He points out that there are at least 14 types of connexin in humans. The reduction but persistence of gamma synchrony in the absence of Cx36 is consistent with it being one of a number of similar proteins involved in the performance of gap junctions. Conventional text books do not seem to support Koch's view of the knock out potential of Connexin 36. Connexins are the proteins which span the fixed 2-4nm gap by which gap junctions separate cells. The cells are coupled both electrically and metabolically. Six subunits of connexin together form a gap junction channel known as a connexon. This allows an aqueous channel between the interiors of the two neurons involved. Small molecules, such as amino acids, with a mass of less than 1,000 daltons can pass through the connexin, but larger molecules such as proteins cannot. A gap junction can comprise a large number of such connexons. Gap junctions in different tissues have different properties, as a function of the different connexins that form the junctions in these particular tissues. However, particular types of connexin can be present in a range of tissues. Most types of cell have examples of more than one type of connexin. It is common for two types of connexin to be present in the same connexon, and where neighbouring cells do have different types of connexin, they can form connexons that contain both types of connexin. The existence of so many connexins and the ability to mix connexins and to express the same type of connexin in different types of tissue seems to argue against the idea that the absence of one connexin can knock out gap junction function as such. Unrelated to the experiments with Connexin 36, it has been shown that the absence of connexin 43 can cause problems with the development of the heart. From our point of view, the significance of this seems to be that there is still a gap junction without connexin 43 and probably without 36 as well. The Hameroff proposal for quantum tunelling at the junction does not require any particular connexin to be present in the structure. The final discussion between Koch and Hameroff relates to the actual action of anaesthesia. Here Hameroff is on his own ground as an anaesthetist, and can reasonably be seen as authoritative. Koch claims that a host of body processes such a heart and breathing are effected by anaethetics, while Hameroff states that if the dose is correct patients routinely breathe on their own, unless separate muscle paralysing agents are used. This debate is significant relative to the debate as to whether consciousness is something physically distinct from other brain and body processes. 5.) Quantum computation in brain microtubules? Stuart Hameroff Some philosophers have suggested that qualia, the basic elements of subjective experience constitute a fundamental level of reality. To look at this from a scientific point of view, the nature of physical reality, as described by relativity and quantum theory must be examined. In respect of this, as described by relativity and quantum theory must be examined. In respect of this, Roger Penrose takes the position that the quantum wave function collapse is a real event rather than an abstract mathematical concept, as in the traditional Copenhagen interpretation. He has proposed a new version of the collapse, known as Objective Reduction (OR). This occurs if quantum superpositions do not interact with the environment for some sufficient length of time, in which the superpositions begin to form separate spacetime geometries, which in turn forces them into collapse. Penrose suggests that this objective reduction provides a link to the fundamental level of spacetime that encodes the non-computible processing of human mathematical understanding and possibly also the qualia of subjective experience. In the normal wave function collapse, the selection of a state for a particle is random. Penrose suggests that in the case of objective reduction, the selection is neither random nor deterministic, but the outcome of a non-computable process, and as such the basis of human understanding. He furtheer claimed that Godel's theorem showed that the human brain sustained non-computable processing. In the Penrose/Hameroff model, microtubules are the suggested location of objective reduction activity. Microtubules are comprised of subunits formed from the protein tubulin. The tubulin protein subunit is an 8nm dimer comprising two 4 nm monomers. This can undergo a conformational change putting the monomer at an angle to the axis of the dimer. Studies show large hydrophobic pockets in which van der Waals quantum forces can govern the action of protein. Recent evidence indicates signalling along microtubules. Microtubules interact with the cell membrane via linking proteins and are involved in forming and maintaining synaptic connections. Quantum superpositions are proposed to arise in these tubulins, with each subunit recruiting other subunits into a macroscopic quantum state. When the superpositions collapse , they select states of the tubulins that in turn influence synaptic functions. Microtubules were on the right scale for collapse to occur on a neurally useful timescale. Too small a scale, such as that of a single electron would involve an impossibly long timescale, while too large a scale would involve much too rapid a collapse. The main argument against quantum consciousness is the apparently likley rapid collapse of quantum features in the conditions of the brain. Penrose argues that microtubules could be screened from such decoherence by ordering of water around their surface and by the coherent pumping of biochemical energy in a system that is far from thermal equilibrium. 6.) Conscious events as orchestrated spacetime selection Stuart Hameroff & Roger Penrose Quantum superpositions represent many possible states that have values weighted by complex numbers, reducing to a single eigenstate when the wave function collapses. The result is random but can be weighted according to probability. In early experiments the collapse of the wave function was related to deliberate observation by scientists and their instruments. However, the question of what happened to unobserved wave functions was side lined. Penrose has proposed a form of objective reduction of the wave function for situations in which quantum superpositions have continued long enough for their individual spacetime geometries to become separated by more than the Planck length, at which point the scale of separation becomes unstable and collapses. Microtubules are seen as the best candidates within the brain for such objective reductions to occur. However, clatharins, vesicular grids and neural membrane proteins are also considered to be possible sites. Microtubules possess a range of features that make them suitable for a combination of quantum coherence and information processing. They are widespread throughout the brain, have functional effects, a periodic structure, and may be capable of being temporally isolated from the environment. 7.) Quantum computation in microtubules: in the Philosophical Transactions of the Royal Society (1998) Stuart Hameroff Quantum computation has been shown to have a number of applications beyond those that can be achieved by a classical computer. Conventional theories of consciousness assume that consciouness emerges from brain processing that is analogous to a classical computer. The concepts main flaw is its inability to account for subjective consciousness, as distinct from information processing, added to which is its lack of description of any difference between conscious and unconscious processing in the brain. Quantum computing requires either very low temperatures or energy pumping. Hameroff criticises some commentators on the Penrose/Hameroff theory for failing to realise that there is a difference between quantum computers as now under development and the consciousness as proposed by Penrose. Presently planned quantum computers would see their wave functions collapse as a result of interaction with the environment. Non- computability and consciousness can only arise if superpositions survive for long enough to collapse as a result of Penrose's proposed separation of spacetime geometries. Planned quantum computers would not be conscious and would be deterministic rather than non-computable. 8.) Consciousness, the brain and spacetime geometry Stuart Hameroff Annals of the New York Academy of Sciences Penrose proposes that spacetime is not continuous but comprises a web or network, such as his idea of spin networks, where a spin network codes for each quantum state. Spin networks define volumes and configurations that evolve dynamically. These networks operate at the Planck length, where the continuity of spacetime is perceived to break up. Penrose starts with the general relativity concept of spacetime curvature, where the curvature in different directions of two superpositions with different spacetimes, results in a speparation or blister in spacetime. This blister becomes unstable if it exceeds the Planck length, resultinng in objective reduction and a reconfiguration of spacetime. P Protein and specifically tubulin protein is seen as a basis for objective reduction in the brain. Proteins are only marginally stable and undergo frequent change. They are macromolecules that perform a variety of functions by changing their configuration. The driving force in protein is seen to be non-polar groups of amino acids that form into hydrophobic pockets in the protein interior by means of van der Waals forces. Anaesthetic gases have their effects in such pockets. Dipole to dipole forces are known as van der Waals forces. They can be permanent dipole to permanent dipole effects, permanent dipole to induced dipole effects or induced dipole to induced dipole. These last are called London forces and are the weakest type of van der Waals force. They form in atoms and molecules that are otherwise electrically neutral. They are 40 times weaker than hydrogen bonds. They are important to the action of protein. Such activity is suggested to allow interaction between tubulins. 9.) Review of Roger Penrose's 'The Large, the Small and the Human Brain' by Brian Josephson In discussing Penrose's proposal for an objective reduction of the wave function, Josephson takes the disappointing approach of stating that Penrose's ideas are insufficient without actually discussing what is proposed or more specifically what he disagrees with. In going on to discuss Penrose's arguments relative to the Godel theorem, Josephson appears to rely on majority opinion rather than working out an actual argument. It appears likley that a majority of logicians do oppose Penrose, but this again is coming to have the appearance of an en bloc knee jerk reaction rather than individually developed views. In particular, Josephson seems to place an undue degree of reliance on the 1995 Grush and Churchland article which argued from the fact that mathematicians could make mistakes. This is essentially a truism, and fails to look at the more relevant case of incontrovertible mathematical arguments, such as the Goldberg conjecture. 10.) Inflationary theory and the early universe - from Roger Penrose's 'Road to Reality' The concept of inflation in the early universe is an important theme in recent cosmology. The inflationary period is seen as a time during which a multiverse of different universes could have been spun off, with our universe being just one amongst many, or even an infinity of universes. P The observed 'fine tuning' of our universe creates impossible odds against our universe having arisen on its own and by chance from a single fluctuation in the vacuum. The idea of a multiverse overcomes this problem by allowing an infinity of unverses of which ours is only one. An inflationary period in the very early universe is suggested to have allowed the creation of a multiverse. As so often, Penrose is out-of-line with fashionable thinking, and argues against inflation theory in his book, 'Road to Reality.' Much of the discussion here deals with the second law of thermodynamics and the increase in entropy. Penrose conceives of entropy as different sizes in phase space, which is conceived as containing six dimensions, three for position and three for momentum. The amount of entropy and therefore phase space gets smaller and smaller as we go further back towards the Big Bang. The source of the second law, by which entropy increases lies in a tiny volume of phase space at the Big Bang. The uniformity of the Big Bang corresponds to very low entropy. Penrose discusses the 'horizon problem', the fact that the observed temperature of the universe is nearly the same in all directions. This can be explained by the universe having been in thermal equilibrium. This in turn can be explained by an inflationary proceess very rapidly blowing the universe up from a small to a large size. Penrose's criticism of this approach relates to the second law. If there was thermal equilibrium at the start of the inflationary phase, this would represent an increase in entropy prior to the inflationary phase, and therefore an even lower state of entropy at the beginning of the universe, which makes it even more unlikley that it could have arisen from a chance fluctuation in the vacuum. 11.) Dendritic synchrony moves through the brain to mediate consciousness Stuart Hameroff Depts. of Anesthesiology and Psychology, Centre for Consciousness, University of Arizona Journal of Biological Physics, 2009 Introduction: The paper argues that rapidly shifting networks of dendrites connected by gap junctions instantiate the conscious processing of the brain, and focus on particular but also continually changing areas of the underlying non-conscious processing of axons. Hameroff emphasises that conscious and non-conscious processing in the brain cannot always be regarded as separate and distinct. He points out that we can perform many routine functions unconsciously, but when a novel or hazardous situation arises, we flip over into conscious handling of the situation. The best correlate of consciousness is phase synchrony at specific EEG frequencies recorded from different electrodes on the scalp or brain surface. Phase synchrony at a particular frequency can occur within one brain region, between neighbouring brain regions, between distant brain regions or between many spatially separated brain regions. Wolf Singer et al (1.) found that phase synchrony was connected to conscious perception within the (30-90 Hz) gamma band. Subsequent studies have shown gamma synchrony in a number of locations correlating with conscious perception, motor control, language, working memory, face recognition and sleep/dream cycles. The binding problem, as to why consciousness of different modalities is perceived as a unified whole can also be addressed via the gamma synchrony (2-9.). Specific types of consciousness content are correlated with with particular distributions of gamma synchrony in the olfactory bulb dendrites, and conscious experience of pleasure with gamma synchrony in the ventral tegmentum and nucleus accumbens (10-13.). Moreover, the distribution of gamma synchrony within the brain can change in a matter of hundreds of milliseconds and sometimes faster. Hameroff envisages the gamma synchrony as something that focuses on particular areas of the underlying non-conscious processing in neurons. Hameroff is critical of conventional views that have seen dendritic and somatic processing of inputs from synapses as a passive affair. He points to complex signalling within and between dendrites, and in cytoskeletal somatic processing (14-16.). As an anaesthetist, Hameroff points out that anaesthetics act almost exclusively on dendritic and somatic proteins rather than on axonal proteins. Experiments in the 1990s showed that the gamma synchrony seen in various brain regions required dendrite-to-dendrite gap junctions binding together groups of neurons. In the cortex, interneurons have a large number of dendrites and form connections with up to 70 neurons or glia cells. Interneurons often form both a synapse and a gap junction with another neuron. In layers 2 to 6 of the cortex, interneurons form gap junctions with neurons in all other layers, meaning that a gap junction mediated web pervades the cortex. The dynamics of such a web are determined by whether the gap junctions involved are opened or closed. A number of elements in the brain act to determine this opening/closure, including G protein activity, calcium ions and microtubules, the last of which relate to the Penrose/Hameroff model of consciousness. The synchronised dendritic web activity changes as the gap junctions open and close. The number of different possible dendritic webs formed amongst billions of neurons and glia is described as near-infinite. Axonal firing is found to be different when neurons are synchronised from when they are acting individually, suggesting that involvement in the dendritic webs described is efficacious for neurons. This last is relevant in consciousness studies, where it is often asserted that consciousness cannot be efficacious in the brain. References:- 1.) Gray, C., Singer, W. et al - Oscillatory responses in visual cortex - Nature, (1989), 338, pp. 334-7 2.) Llinas, R. & Ribary, U. - Coherent 40 Hz oscillation characterises dream state - Proceedings of the National Academy of Sciences, (1993), 90, 2078-81 3.) Tiitinen, H. et al - Selective attention enhances 40 Hz response - Nature, 364, pp. 59-60 4.) Tallon-Baudry, C. et al - Oscillatory gamma band activity induced by visual search - Journal of Neuroscience, (1996), 16, 4240-49 5.) Miltner, W. & Taub, E. et al - Coherence of gamma band activity as a basis for learning - Nature, (1999), 397, pp. 434-6 6.) Fries, P. & Singer, W. et al (2002) - Oscillatory synchronisation in visual cortex as a correlate of stimulus selection - Journal of Neuroscience, (2002), 22 (9), 3739-54 7.) Mashour, G. (2004) - Consciousness unbound: towards a paradigm of general anesthesia - Anesthesiology, 100, pp. 428-33 (2004) 8.) Garcia-Rill, E. et al (2007) - Electrical coupling: novel mechanism for sleep wake control - Sleep, (2007), 30 (11), 1405-14 9.)Melloni, L., Rodriguez, E. et al, (2007) - Synchronisation of neural acivity correlates with conscious perception - Journal of Neuroscience, 27 (11), 2858-65 10.) Christie, J., Hormuzdi, S. et al (2005) - Connexin 36 synchrony in olfactory bulb - Neuron, 46 (5), 761-72 11.) Christie, J. (2006) - Lateral excitationwithin the olfactory bulb - Journal of Neuroscience, 26, (8) 12.) Rash, J. et al (2005) - Ultrastructual localisation of connexins (Cx 36, Cx 43, Cx 45) in olfactory bulb - Journal of Neurocytology, 34, (3-5), 307-41 13.) Lassen, M. et al (2007) Brain stimulation reward is integrated by a network of electrically coupled neurons - Brain Research, 1156, pp. 45-58 14.) Shepherd, G. - The dendritic spine - Journal of Neurophysiology, 75, 2197-2210 15.) Sourdet, V. - Dendritic filtering in associative long-term synaptic plasticity - Learn Mem., 6, (5) pp. 422-47 16.) Poirazi, P. (2001) - Dendrites, plasticity, memory capacity of neural tissue - Neuron 29 (3), pp. 779-96 12.) Conditions for coherent vibrations in the cytoskeleton J. Pokorny, Academy of Sciences of the Czech Republic Bioelectrochemistry and Bioenergetics (1999) INTRODUCTION: Prokorny suggests that the polarity of vibrational structures in organic matter can lead to coherent states and energy condensation. Microtubules are suggested to satisfy this requirement. Pokorny says that mechanisms governing the high degree of organisation in living organisms are largely unknown. The type of spatial order seen with inorganic crystalline substances is not apparent in organic matter, such as microtubules and actin filaments, and it is generally agreed that the self assembly and ordering of living matter is based on mechanisms peculiar to biological systems. Biological matter has polar properties suggesting that there are electromagnetic aspects to its organisation. Pokorny discusses at some length proposals by Frohlich, who postulated that long-range quantum mechanical phase correlations could exist in biological systems. His ideas were based on three concepts, the polar nature of biological structures, energy supply to the system, and energy transfer between oscillators within the system. Some modes of motion could become strongly excited, and remain far from thermal equilibrium. The polar nature of biological objects made it likely that this would lead to longitudinal oscillations. His calculations suggested that these processes could produce a form of of quantum coherence capable of supporting dissapationless transfer of energy similar to that seen in superconductivity. Pokorny argues that microtubules have the right structure to generate this type of energy. The tubulin sub-components are electrical dipoles, and the microtubules as a whole are polar structures, with positive and negative ends. Vibrations in such a polar system give rise to an electromagnetic field. Energy is exchanged between the vibrating structure and the region around it. It is suggested that some of the energy involved in conformational changes in the tubulin proteins of microtubules could be transformed into vibrational energy. The altered forces between the protein subunits of the microtubule would supply energy to the whole microtubule lattice. The energy thus stored in the microtubule can do work in the cell, and Pokorny considers it possible that polarisation waves may become coherent on the basis of Frohlich's calculations. It is thought possible that polar vibrations do work in the vicinity of the microtubule. Pokorny further suggests that the electromagnetic activity observed in living cells such as yeast cells may be relevant to the activities in microtubules. |
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