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Quantum mind

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The quantum mind or quantum consciousness hypothesis proposes that classical mechanics cannot explain consciousness, while quantum mechanical phenomena, such as quantum entanglement and superposition, may play an important part in the brain's function, and could form the basis of an explanation of consciousness. There are several quite distinct quantum mind theories, and these are discussed in the sections below.

Description of main quantum mind approaches

David Bohm

David Bohm took the view that quantum theory and relativity contradicted one another, and that this contradiction implied that there existed a more fundamental level in the physical universe.[1] He claimed that both quantum theory and relativity pointed towards this deeper theory. This more fundamental level was supposed to represent an undivided wholeness and an implicate order, from which arose the explicate order of the universe as we experience it.

Bohm's proposed implicate order applies both to matter and consciousness, and he suggests that it could explain the relationship between them. Mind and matter are here seen as projections into our explicate order from the underlying reality of the implicate order. Bohm claims that when we look at the matter in space, we can see nothing in these concepts that helps us to understand consciousness.

In trying to describe the nature of consciousness, Bohm discusses the experience of listening to music. He thinks that the feeling of movement and change that make up our experience of music derives from both the immediate past and the present both being held in the brain together, with the notes from the past seen as transformations rather than memories. The notes that were implicate in the immediate past are seen as becoming explicate in the present. Bohm views this as consciousness emerging from the implicate order.

Bohm sees the movement, change or flow and also the coherence of experiences, such as listening to music as a manifestation of the implicate order. He claims to derive evidence for this from the work of Jean Piaget[2] in studying infants. He states that these studies show that young children have to learn about time and space, because they are part of the explicate order, but have a "hard-wired" understanding of movement, because it is part of the implicate order. He compares this "hard-wiring" to Chomsky's theory that grammar is "hard-wired" into young human brains. In his writings, Bohm never proposed any specific brain mechanism by which his implicate order could emerge in a way that was relevant to consciousness.

Henry Stapp

The physicist, Henry Stapp, bases a theory of consciousness on Heisenberg’s interpretation of quantum theory [3] Heisenberg thought that quantum theory was something more than a system of statistical rules, and that the probability distribution of quantum theory really existed in nature. He considered that the evolution of this probability distribution was punctuated by uncontrolled quantum wave collapses, which are the events that actually occur in nature, and the manifestation of which eliminates the other possibilities in the probability distribution.

The emphasis is thus on the probability distribution. Heisenberg did not view the quanta as actual things, but as tendencies for certain types of events to occur. The orderly evolution of the quantum system is deterministic, but this controls only the tendency for things or propensity for events and not the actual things or events themselves. The things or events are controlled by quantum jumps that do not individually conform to any natural law, but collectively conform to statistical rules.

Stapp envisages consciousness as exercising top-level control over neural excitation in the brain. Quantum brain events are suggested to occur at the whole brain level rather than the level of the synapses. In this system, conscious events are selected from the large-scale excitation of the brain. Stapp speaks of a creative event bringing into being one of a range of possibilities that exist in Heisenberg’s quantum distribution of probabilities. The neural excitations are a code, and each experience is regarded as a selection from this code. The conscious brain is seen by Stapp as a system that is internally determined in a way that cannot be represented outside the system, whereas in the rest of the physical universe an external representation of an object or system and knowledge of the laws of physics allow accurate predictions as to future events.

Stapp views the brain as a self-programming computer with self-sustaining input from memory, which is a code derived from previous experience. This results in a number of probabilities from which consciousness has to select. The conscious act is a selection of a piece of top-level code, which then exercises control over the flow of neural excitation. Each human experience is accompanied by the activation of a top-level code.

Conscious events are seen as being capable of grasping a whole pattern of activity, and this in turn is seen as accounting for the unity of consciousness. Stapp envisages a top level of brain processing involved with information gathering, planning of actions, choice of particular plans and execution and monitoring of these plans. It is suggested that each top-level event is linked to a psychological event, which connects the psychological to the quantum. Each human conscious experience is seen as a ‘feel’ of an event in the top level of processing in the human brain.

Stapp views the physical world as a structure of tendencies or probabilities within the world of the mind. He considers that the introduction of an irreducible element of chance into nature via the collapse of the wave function, as described in most forms of quantum theory, is unacceptable. The element of conscious choice is seen by him as removing chance from nature.

Gustav Bernroider

The neurobiologist, Gustav Bernroider, has advanced a theory of consciousness based on the proposition that the entangled ion states arise in the voltage-gated ion channels of the membranes of neurons. Bernroider's theory was principally developed in a 2005 paper co-authored with the mathematician Sisir Roy. [4]

In this paper, Bernroider and Roy draw on the work of the MacKinnon group relative to the potassium (K+) channel. [5] [6] The MacKinnon group demonstrated that the functioning of the K+ channel occurs in two stages, firstly, the selection of K+ ions in preference to any other species of ion, and secondly voltage-gating that controls the flow of these favoured K+ ions. In its closed state, the channel is now seen to stabilise three K+ ions, two in the permeation filter of the ion channel, and one in a water cavity to the intracellular side of this permeation path. In the case of the channel's voltage gating, the electrical charges involved which were previously thought to act independently of the surrounding proteins and lipids, are now seen to be coupled to these proteins and lipids, and are thus involved in the gating process. The group further showed that the filter region of the channel has a framework of five sets of four oxygen atoms, which are each part of the carboxyl group of an amino-acid molecule in the surrounding protein. These are referred to as binding pockets, involving eight oxygen atoms in total. Both ions in the channel oscillate between two configurations.

Bernroider and Roy's calculations based on this work lead them to claim that ion permeation can only be understood at the quantum level. Their calculations predict that the trapped ions will oscillate many times before the K+ channel re-opens, and the calculations also suggest an entangled state between the potassium ions and the binding oxygen atoms. This structure is seen as being delicately balanced and sensitive to small fluctuations in the external field. This sensitivity is viewed as possibly being able to account for the observed variations in cortical responses. Taking this as an initial assumption, they go on to ask whether the resulting model of the ion channel can be related to logic states. Their calculations suggest that the K+ ions and the carboxyl atoms of the binding pockets are two quantum-entangled sub-systems, and they equate this to a quantum computational mapping. The K+ ions that are destined to be expelled from the channel could, in the authors' hypothesis, encode information about the state of the oxygen atoms in the axon membrane.

These proposals do not appear to have generated discussion at a peer-reviewed or academic press level. However, Guerreschi, G. et al are looking to improve their model of entanglement inn protein (references) to the point where it could test for/falsify theories of non-trivial coherence or entanglement in protein, such as Bernroider has proposed.

David Chalmers

The philosopher David Chalmers has speculated on a number of ways in which quantum mechanics might relate to consciousness.

"One possibility is that instead of postulating novel properties, physics might end up appealing to consciousness itself, in the way that some theorists but not all, hold that quantum mechanics does."[7]

"The collapse dynamics leaves a door wide open for an interactionist interpretation."[7]

"The most promising version of such an interpretation allows conscious states to be correlated with the total quantum state of a system, with the extra constraint that conscious states (unlike physical states) can never be superposed. In a conscious physical system such as a brain, the physical and phenomenal states of the system will be correlated in a (nonsuperposed) quantum state. Upon observation of a superposed external system, Schrödinger evolution at the moment of observation would cause the observed system to become correlated with the brain, yielding a resulting superposition of brain states and so (by psychophysical correlation) a superposition of conscious states. But such a superposition cannot occur, so one of the potential resulting conscious states is somehow selected (presumably by a nondeterministic dynamic principle at the phenomenal level). The result is that (by psychophysical correlation) a definite brain state and a definite state of the observed object are also selected."[7]

"If physics is supposed to rule out interactionism, then careful attention to the detail of physical theory is required."[7]

However, Chalmers is also sceptical about the ability of any kind of New Physics to resolve the Hard Problem of Consciousness:

"Nevertheless, quantum theories of consciousness suffer from the same difficulties as neural or computational theories. Quantum phenomena have some remarkable functional properties, such as nondeterminism and nonlocality. It is natural to speculate that these properties may play some role in the explanation of cognitive functions, such as random choice and the integration of information, and this hypothesis cannot be ruled out a priori. But when it comes to the explanation of experience, quantum processes are in the same boat as any other. The question of why these processes should give rise to experience is entirely unanswered."[8]

"The trouble is that the basic elements of physical theories seem always to come down to two things: structure and dynamics of physical processes. . . . But from structure and dynamics, we can only get more structure and dynamics. . . conscious experience will remain untouched"[9]

Roger Penrose and Stuart Hameroff

The theoretical physicist, Roger Penrose, and the anaesthesiologist, Stuart Hameroff, collaborated to produce the theory known as Orchestrated Objective Reduction, otherwise abbreviated as Orch-OR. Penrose and Hameroff initially developed their ideas separately, and only later cooperated to produce Orch-OR. Penrose came to the problem from the point of view of mathematics and in particular Gödel's theorem, while Hameroff came from a career in cancer research and anaesthesia.

Gödel's theorem is central to this theory. In 1931, Gödel proved that any theory capable of expressing elementary arithmetic cannot be both consistent and complete. Further to that, for any consistent formal theory that proves certain basic arithmetic truths there is an arithmetical statement that is true, but not provable in theory.

The theorem is not in itself controversial, but what Penrose developed from it is. In his first book on consciousness, The Emperor's New Mind (1989), Penrose argued that the theorem showed that the brain had the ability to go beyond what could be achieved by axioms or formal systems. He argued that this meant that the brain had some additional function that was not based on algorithms (a system of calculations), whereas a computer is driven solely by algorithms. Penrose asserted that the brain could perform functions that no computer could perform. He called this type of processing non-computable.

Penrose went on to consider what it was in the human brain that was not driven by algorithms. Given the algorithm-based nature of most of physics, he decided that the random choice of position etc. that occurs when a quantum wave collapses into a particle was the only possibility for a non-computable process. However, Penrose admitted that the randomness of the wave function collapse, although free from algorithms, is not a basis for any useful form of human understanding.

Penrose now proposed a second form of wave function collapse that could apply where quanta did not interact with the environment, but might collapse on their own accord. He suggests that each quantum superposition has its own piece of spacetime curvature, and when these become separated by more than the Planck length of 10−35 metres, they become unstable and collapse. Penrose called this form of collapse objective reduction.

Penrose suggested that objective reduction represented neither randomness nor the algorithm based processing of most physics, but instead a non-computable influence embedded in the fundamental level of spacetime geometry from which mathematical understanding and, by later extension of the theory, consciousness derived.

When he wrote his first book on consciousness, The Emperor's New Mind in 1989, Penrose lacked a detailed proposal for how quantum processing could be implemented in the brain. Subsequently, Hameroff read Penrose's work, and suggested that microtubules could be suitable candidates for quantum processing, an hypothesis which remains intensly controversial. The Orch-OR theory arose from the collaboration of Penrose and Hameroff in the early 1990s.

Microtubules have a well established position in conventional biology and neuroscience. Microtubules are the main component of a supportive structure within neurons known as the cytoskeleton. In addition to providing a supportive structure, the known functions of microtubules include transport of molecules including neurotransmitters bound for synapses and control of the development of the cell. Microtubules are composed of tubulin protein dimer subunits. The tubulin dimers each have hydrophobic pockets that are 8 nm apart, and which may contain delocalised pi electrons. Tubulins have other smaller non-polar regions that contain pi electron-rich indole rings separated by only about 2 nm.

Hameroff proposes that these electrons are close enough to become quantum entangled.[10] In the original version of his proposals, Hameroff went on to hypothesise that these electrons could become locked in phase, forming a state known as a Bose-Einstein condensate.[11][12] In his most recent paper [13], he has amended this to suggest that electrons within the tubulin subunits are part of a Frohlich condensate, which is a coherent oscillation of dipolar molecules.

Furthermore, he proposes that condensates in one neuron could extend to many others via gap junctions between neurons, thus forming a macroscopic quantum feature across an extended area of the brain. When the wave function of this extended condensate collapsed, it was suggested that this could give access to non-computational influences related to mathematical understanding and ultimately conscious experience that are embedded in the geometry of spacetime.

Finally, Hameroff postulated that the activity of these condensates is the source of gamma wave synchronisation in the brain. This synchronisation has also been viewed as a likely correlate of consciousness in conventional neuroscience, and it has been shown to be linked to the functioning of gap junctions.[14][15][16][17][18][19][20][21]

Another neuroscientist, Danko Georgiev, has provided a footnote to the Orch-OR theory. He accepts much of Penrose's ideas, but criticises a good part of Hameroff's scheme. He proposes that quantum coherence on the surface of the microtubules extends via presynaptic scaffold proteins to the synapses, where it both influences synaptic firing, and is transmitted across the synaptic cleft to other neurons.[22]

Recently the debate about Hameroff's proposals has focused round papers by Reimers et al [23] and McKemmish et al [24]and Hameroff's replies to these [13], which is not regarded as being independently reviewed. The Reimer's paper claimed that microtubules could only support 'weak' 8 Mhz coherence, but that the Orch-OR proposals required a higher rate of coherence. Hameroff, however, claims that 8 Mhz coherence is sufficient to support the Orch-OR proposal. McKemmish et al makes two claims; firstly that aromatic molecules cannot switch states because they are delocalised. Hameroff, however, claims that he is referrinng to the behaviour of two or more electron clouds; secondly McKemmish shows that changes in tubulin conformation driven by GTP conversion would result in a prohibitive energy requirement. Against this, Hameroff claims that all that is required is switching in electron cloud dipole states produced by London forces.

Quantum brain dynamics

The ideas behind quantum brain dynamics (QBD) derived originally from the physicists, Hiroomi Umezawa,[25] and Herbert Fröhlich[26] in the 1960s. In recent decades these ideas have been elaborated and given greater prominence by a later generation of physicists such as Mari Jibu[27][28], Kunio Yasue[27][28] and Giuseppe Vitiello.[29] In QBD, the electrical dipoles of the water molecules that constitute 70% of the brain are proposed to constitute a quantum field, known here as the cortical field. The quanta of this field are described as corticons. In the theory, this field interacts with quantum coherent waves generated by biomolecules in the neurons and propagating along the neuronal network.

The physicist, Herbert Frohlich, is the source of the hypothesis that quantum coherent waves could be generated in the neuronal network. Frohlich argued that it was not clear how order could be sustained in living systems given the disruptive influence of the fluctuations in biochemical processes. He viewed the electric potential across the neuron membrane as the observable feature of some form of underlying quantum order. His studies claimed to show that with an oscillating charge in a thermal bath, large numbers of quanta may condense into a single state known as a Bose condensate. This state allows long-range correlation amongst the dipoles involved. Further to this, biomolecules were proposed to line up along actin filaments (part of the cytoskeleton) and dipole oscillations propagate along the filaments as quantum coherent waves. This now has some experimental support in the form of confirmation that biomolecules with a high electric dipole moment have been shown to have a periodic oscillation.[30] Vitiello also argues that the ordered chains of chemical reactions on which biological tissues depend would collapse without some form of quantum ordering, which in QBD is described by quantum field theory rather than quantum mechanics.

Vitiello provides citations, which are claimed to support his view of biological tissue. These include studies of radiation effect on cell growth,[31] response to external stimuli,[32] non-linear tunnelling,[33] coherent nuclear motion in membrane proteins,[34] optical coherence in biological systems,[35] energy transfer via solitons and coherent excitations.[36]

QBD proposes that the cortical field not only interacts with, but also to a good extent controls the neuronal network. It suggests that biomolecular waves propagate along the actin filaments in the area of the cell membranes and dendritic spines. The waves are suggested to derive energy from ATP molecules stored in the cell membrane and to control the ion channels, which in turn regulate the flow of signals to the synapses. Vitiello claims that QBD does not require quantum oscillations to last as long as the actual time to decoherence.

The proponents of QBD differ somewhat as to the exact way in which it produces consciousness. Jibu and Yasue think that the interaction between the energy quanta of the cortical field and the biomolecular waves of the neuronal network, particularly the dendritic part of the network, is the process that produces consciousness. On the other hand, Vitiello suggests that the quantum states involved in QBD produce two poles, a subjective representation of the external world and a self. This self opens itself to the representation of the external world. Consciousness is, in this theory, not in either the self or the external representation, but between the two in the opening of one to the other.

Ongoing debate

The main argument against the quantum mind proposition is that quantum states in the brain would decohere before they reached a spatial or temporal scale, at which they could be useful for neural processing. This argument was elaborated by the physicist, Max Tegmark. Based on his calculations, Tegmark concluded that quantum systems in the brain decohere quickly and cannot control brain function. He states that "This conclusion disagrees with suggestions by Penrose and others that the brain acts as a quantum computer, and that quantum coherence is related to consciousness in a fundamental way".[37][38]

A recent paper by Engel et al. in Nature does indicate quantum coherent electrons as being functional in energy transfer within photosynthetic organisms, but the quantum coherence described lasts for 660 fs[39] rather than the 25 milliseconds required by Orch-OR, and this is compatible with Tegmark's calculations. More recent papers involving Guerreshi, G., Cia, J., Popescu, S. and Briegel, H. [40] are looking to improve their model of entanglement in protein, a test which could falsify theories, such as those of Penrose and Hameroff, that require non-trivial coherence or entanglement in protein. In their reply own reply to Tegmark's paper, also published in Physical Review E, the physicists Scott Hagan, Jack Tuszynski in collaboration with Hameroff [41][42] produced counter proposals to the effect that the interiors of neurons could alternate between liquid and gel states. In the gel state, it was further hypothesized that the water electrical dipoles are oriented in the same direction, along the outer edge of the microtubule tubulin subunits. Hameroff et al. proposed that this ordered water could screen any quantum coherence within the tubulin of the microtubules from the environment of the rest of the brain.

In the last decade some other research has been argued to favour quantum theories of consciousness. Between 2003 and 2009, Elio Conte and co-authors performed a number of experiments interpreted as evidence for "possible existence of quantum interference effects on mental states during human perception and cognition of ambiguous figures".[43][44] Further, in a 2011 paper in Physical Review Letters,it is argued that the sensitivity of European robins to small changes in the prevailing magnetic field is evidence that "superposition and entanglement are sustained in this living system for at least tens of microseconds, exceeding the durations achieved in the best comparable man-made molecular systems", and the authors produce a simple model to this effect.[45][46][47]

See also

References

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Further reading