Neuroscience and quantum mechanics
Author: Javier Sánchez Cañizares
Published in: Neuroscience and Quantum Mechanics. Diccionario Interdisciplinar Austral, edited by Claudia E. Vanney, Ignacio Silva and Juan F. Franck.
Date of publication: 2016.
summaryIn recent years, progress in the field of neuroscience has stimulated interest in better understanding the relationship between the mind and the brain. Quantum Mechanics (QM) has been present in this field practically from the beginning, starting with its well-known "paradox of measurement". The standard interpretation of QM assumes the existence in nature of two fundamental and irreducible processes: the deterministic evolution of the wave function according to the Schrödinger equation (once the initial and boundary conditions have been established) and the indeterministic collapse of the wave function after a measurement has been made. Thus, CM would be pointing out the limitations of a purely deterministic view of nature and, in particular, of brain activity.
However, the relevance of CM for brain physics is highly controversial. Detractors of its influence rely on the role of decoherence processes to ensure a classical and deterministic behavior of the brain, without paying much attention to the philosophical assumptions involved in resource to quantum decoherence in the mind-brain problem (Sánchez-Cañizares 2014). In this voice, after introducing an overview of the relations between neuroscience and CM (section 1) and explaining why the latter might be relevant to the former (section 2), we will review the most important models involving CM in the brain, making explicit their position regarding the causal relations between brain activity and conscious experience (section 3). The main criticisms of the relevance of CM for neuroscience will be presented (section 4) and the physical and epistemic implications of resource to decoherence will be discussed (section 5) before presenting some philosophical considerations that highlight the need for an interdisciplinary approach to discussion (section 6). We will devote the last section to some brief conclusions. Thus, we will focus here on the relationship between neuroscience and quantum mechanics in the context of the mind-brain problem and, in particular, of consciousness.
The field of neuroscience has been receiving increasing attention due to theoretical and empirical progress in the understanding of the brain. The dream of reaching a scientific view final of the relations between the human mind and brain seems to be getting closer and closer, following experimental results such as those presented by Libet and other collaborators (Libet, Wright and Gleason 1982), which would indicate a temporal priority of physiological events over consciousness when it comes to action. Closely related to the above, the problem of the ontological status of freedom continues to generate relevant discussions among neuroscientists and philosophers (K. Smith 2011).
Nevertheless, neuroscience's search for the neural correlates of consciousness remains unresolved. The usual budget is that consciousness is the result of a huge issue of neurons working in unison (C. U. M. M. Smith 2009). The classic research scheme of neuroscience aims to find circuits of interconnected neurons whose shape and firing frequency correlate unambiguously with conscious experiences above a certain threshold. Under such assumptions, cognitive neuroscientists and neurobiologists consider CM to be irrelevant to their specific problems (Koch and Hepp 2006); even though the physics of the brain must obey the laws of CM, its most salient features are not exploited. Neuroscience usually moves within the paradigm of classical physics, which considers it possible to describe any system - no matter how complex - by classical computation. According to this widespread view, living systems obey physical laws that would be in contradiction with the possibility of making conscious and free choices. The latter would simply be reflecting the configuration Chemistry of the individual at the time of the (supposed) decision. Therefore, the belief in freedom would be nothing more than a residue of faith in vitalism (Cashmore 2010).
Undoubtedly, the complexity of the brain makes it quite difficult to establish a physical model about the way it works. However, the phenomenon of deterministic chaos has been providing an acceptable context in which to study neural dynamics (Freeman 1979; Amit 1989). Its influence has been growing over the last few years and there is now a general consensus on the essential role of chaotic processes in understanding brain dynamics at various levels. Cognitive science and psychology have adopted this idea (Atmanspacher and Rotter 2008). Within this paradigm, only a small issue of neurons would end up being manager of conscious experiences. Infinitesimal changes in the initial conditions of any process would lead to divergent trajectories in phase space, thus causing the illusion of free action. The mind would emerge from deterministic chaos in the brain and thus consciousness would remain an illusion (Dennett 1991; 2003; Churchland and Sejnowski 1992; Crick 1994; Rees et al. 2002).
According to physicist Anton Zeilinger, the central paradigm of most biologists is that we are essentially classical machines (Abbott et al. 2008). Thought would be material and thinking would be nothing more than subject in coordinated motion. Thought would emerge as a coherent patron saint in a multidimensional system (the human being) coupled to the world, in which the smallest fluctuation can cause a thought to emerge (Kelso 2008). From agreement with the principles of classical physics, consciousness would not make any difference in behavior: all behavior is determined by microscopic causation without the need to make reference letter to consciousness. Thus, philosophers who accept the framework of ideas of classical physics must conclude that conscious experiences are identical with the physical activities of the brain, or simply emergent properties (Stapp 2001). The theory of identity between mind and brain asserts that mental states, qualia, are identical with certain neural states. Today, this is the dominant philosophical perspective on mind in neuroscience, and the basis of most of the neurobiological research on consciousness (Kauffman 2008).
But the question is not so simple from a methodological point of view. Neuroscience has difficulty in identifying the crucial connection between the empirical programs of study , described in psychological terms, and the obtained data , described in neurophysiological terms (Conte et al. 2009). In other words, the correlation between physical and mental states is unclear. In order to establish such a correlation, one needs an account goal or a hypothesis about the state of another person's mind. But can this be done without inaccuracies? Is it possible to know someone's state of consciousness without that person revealing it? Indeed, we contemplate an ongoing discussion about methodological issues related to the introspective methods and subjective reports involved in the research and measurement of consciousness (Irvine 2012).
However, the most profound criticisms of the mind-brain identity theory come from what David Chalmers has called the "hard problem" of neuroscience (Chalmers 1995): how it is possible for the physical activity of neurons to become the phenomenal conscious experience and subjective feelings that we experience. The problem is that the process through which the brain generates thoughts and feelings remains unknown; physical mechanisms and computation cannot explain why we have feelings, consciousness, and "inner life" (Pregnolato 2010). No feature, configuration, or activity of the physical world-as conceived and described by classical physics-can give rise to the experience that characterizes our conscious thoughts, ideas, and feelings (Stapp 2001; Pereira 2003; Kauffman 2008). Consciousness remains totally unexplained by classical means and something beyond the classically conceived physical world seems to be needed to advance the problem (Stapp 2008; 2009; Abbott et al. 2008). The problem of mind-brain relations is thus closely linked to our progress in understanding nature.
Since our classical world is ultimately grounded in QM, this must also be the case in brains and the processes that take place in them. For example, quantum theory is necessary to explain the states of ions in the selection filter and the function of ion channels in neurons (Salari et al. 2011; Summhammer 2012). There is no doubt that quantum phenomena occur and are effective in the brain just as in the rest of the material world. But whether such processes are effective and relevant to those aspects of brain dynamics that correlate with mental activity is debatable; quantum processes would not necessarily be directly responsible for the generation of conscious percepts (Thomsen 2008; Atmanspacher 2011). Theoretically, Planck's constant is an extremely small issue on the scale of human phenomena, so we could judge a classical approximation in any modeling of the brain to be good. However, the MC encompasses subtle nonlocal entanglements of physical quantities that can have macroscopic manifestations - think of phenomena such as superconductivity, superfluidity, Bose-Einstein condensation, or changes in magnetic susceptibility (Ghosh et al. 2003). We do not possess a universal criterion by which such effects can be ignored (in terms of Schrödinger's cat paradox, there is no well-defined threshold of "gateity"), so CM should not be so easily rejected.
Particularly interestingly, Roger Penrose has extended Lucas's early work (Lucas 1961) by arguing that certain aspects of human consciousness, such as understanding the truth of some mathematical propositions, are beyond the possibilities of any computational system (Penrose 1989; 1994; 2004). Non-computability is a well-defined mathematical concept, but it had not previously been considered as a serious possibility for certain physical processes. The argument that conscious thought-regardless of other attributes it may have-is noncomputable (as follows from certain deductions from Gödel's theorems) would imply that at least some conscious states cannot be derived from previous states by an algorithmic process (Hameroff and Penrose 1996; Penrose and Hameroff 2011). Then, neural electrochemical networks would prove radically incapable of generating such dimensions of knowledge, so that the instructions for the neuroscientific research of intelligence would be undermined (Reimers et al. 2009). Within this scientific puzzle, MC could be important because it inherently contains non-algorithmic elements and is the only source fundamental of pure randomness in our current understanding of physical nature (Eagle 2013). It has also been argued that if consciousness is in part quantum, problems associated with the physical causal closure of the brain, freedom, mental causation, and mental experiences might find a way forward (Kauffman 2008; 2009). QM would allow a different "interaction" between the mind and the physical brain.
On the other hand, quantum coherence seems to be a plausible mechanism for the efficiency and coordination exhibited by many living systems, providing a conceptual bridge between the physical organizationChemistry of the living and the phenomenal states of life and experience (Salari et al. 2011). For example, consciousness does not seem to be localized in any part of the brain and yet the person feels as a coherent unit. CM could provide an explanation of such a holistic phenomenon, which resists a purely local analysis, introducing Degrees of essentially non-local freedom. Certainly, non-local Degrees of freedom can be found at higher levels of complexity of certain classical systems, but the latter are not considered "fundamental" in a classical ontology, being inevitably linked to limits in the resolution of observations (Hagan et al. 2002).
The essential non-computability of CM and the mind-brain problem of neuroscience are related through the well-known "paradox of measurement". In the standard interpretation of CM, we find two quite distinct processes: (i) the unitary and deterministic evolution of the wave function according to the Schrödinger equation, once the initial and boundary conditions have been established; and (ii) the non-unitary and random collapse of the wave function, after a measurement has been made, into one of the possible outcomes of that measurement, with a probability given by the square of the absolute value of the amplitude of the possible result before the measurement. How can the discontinuous and probabilistic collapse of the wave function arise from the interaction (measurement) between two parts of the same physical reality? This is the problem or paradox of measurement in MC. The collapse of the wave function is essentially unpredictable and non-computable. Recall in this the non-computable nature of consciousness (Penrose 1994). Hence, for Penrose, those systems capable of multiplying the collapse are good candidates for the physical instructions of consciousness.
This description implies something even more far-reaching for the neuroscience of free conscious will. The concrete measurements made in experiments are not determined by the CM itself and are treated in internship as free variables, to be determined by the observer. The numbers that appear in classical physics represent the internal properties of a physical system, without reference letter to anything external to it; while the action that replaces the function of such numbers in MC represents a specific measurement performed on the physical system by an observer external to it. That is, the quantum generalization of the laws of classical mechanics cannot by itself generate a completely deterministic physical dynamical theory. There is a causal gap. While the Schrödinger equation fits perfectly into a purely classical account goal, the occurrence of actual events requires a non-computable, indeterministic process that is carried out by a measuring device: an observer. The standard interpretation of QM hopelessly conflates the objective and subjective dimensions of reality.
Throughout the history of CM, even more radical perspectives have come to appear within this interpretative framework . London and Bauer (London and Bauer 1939) proposed that human consciousness is actually what determines any measurement, attributing to "creative action of consciousness" the crucial role in understanding CM. London and Bauer (London and Bauer 1939) proposed that human consciousness is in fact what determines any measurement, attributing to the "creative action of consciousness" the crucial role in the understanding of CM. Wigner (Wigner 1967) continued with this hypothesis. But, some years earlier, von Neumann (Von Neumann 1955) succeeded in showing that the boundary separating the measuring instrument and the observed system can be arbitrarily shifted and, ultimately written request, the observer becomes the "abstract ego" (according to von Neumann's terminology ) of the observation (Manousakis 2006; Atmanspacher 2011). Von Neumann makes it clear that his purpose is to unite the subjective perceptual and objective physical aspects of nature. In fact, his theory essentially turns out to be a theory of the interaction of subjective realities with an evolving physical universe goal (Stapp 2001).
At summary, the collapse of the wave function is considered to be accompanied by the experience associated with the chosen measure in the stream of consciousness of the observer. Thus, the agent acquires knowledge (Stapp 2005). The CM includes the description of some effects that cannot be ascribed only to a physical origin, but also include our mental activity. It establishes a deep link between conceptual entities and physical entities (Bohm 1990), resulting in both a description of physical reality and a theory about human knowledge , as already emphasized by Heisenberg (Stapp 2008). The orthodox interpretation of CM is essentially subjective and epistemic, since the fundamental reality of the theory is our knowledge (Stapp 2001). In this status, it is necessary to inquire whether CM in its present form presents unambiguous predictions about the manifestations of mental realities in the brain, or is itself a still incomplete theory about the physical reality that could explain consciousness when it is completed. We will call the latter possibility "quantum bottom-up consciousness" and the former "quantum top-down consciousness" when classifying current models that draw on QM to address the mind-brain problem at framework in neuroscience.
There are several programs of study in the scientific literature that summary models that apply CM to the problem of consciousness (Tuszynski 2006; Vannini 2008; C. U. M. Smith 2009; Atmanspacher 2011), but they do not usually consider whether they imply bottom-up or top-down causality. Here we will present the most relevant models according to this criterion. However, before presenting the main candidates, it is necessary to dedicate some space to a current of research that uses the mathematical formalism of CM to describe phenomena of human consciousness and behavior. These are general approaches that deal with purely mental phenomena using formal features of QM, such as non-commutative operations or non-Boolean logics, but without fully applying the framework of quantum reference letter : they declare themselves "agnostic" with respect to the existence of relevant quantum physical activity in the brain. Some of the most important groups are listed in (Atmanspacher 2011); see, e.g., (Conte 2008; Conte et al. 2009; Pothos and Busemeyer 2012).
Undoubtedly, the CM formalism has the potential to adjust for deviations from the laws of classical probability that appear in certain mental activities. But this approach has been criticized for being ambiguous. It is possible that classical probability models, with different assumptions, may be able to fit experimental results with similar accuracy (Thomsen 2008). The direct application of the CM formalism to mental states allows for a particularly valid statistical fit of many empirical data , but does not quite tell us anything about the underlying reality manager of such mental phenomena (Atmanspacher 2011). Nevertheless, such a formalism could offer unambiguous results about the relevance of CM to the neuroscientific problem of mind-brain relations, insofar as it can show the inability of classical models to explain the available results.
Probably the best-known bottom-up theory of quantum consciousness is Penrose and Hameroff's hypothesis that the tubulins of microtubules - filament-like protein polymers present in the cytoskeleton of neurons - carry out quantum computations (Hameroff and Penrose 1996; 2014; Hameroff 2007; Penrose and Hameroff 2011). The reason adduced by Penrose for resorting to QM is not that its intrinsic randomness gives room for mental causation to be effective. His conceptual starting point is that the emergence of a conscious act is a process that cannot be described algorithmically. Hameroff, for his part, realized that Penrose's ideas about the non-computability of consciousness could complement his own work about microtubules, in which tubulins would neurophysiologically embody Penrose's conceptual framework . Tubulin states appear to depend on quantum events, so that quantum coherence between different tubulins is possible (Abbott et al. 2008; C. U. M. M. Smith 2009; Atmanspacher 2011).
Each tubulin can be in two superimposed configurations, corresponding a specific geometry of space-time to each configuration. When the separation between the energies of these two configurations reaches a critical threshold, in the regime of a quantum gravity, the objective reduction (OR) of the wave function to one of the two configurations must occur (Hameroff and Penrose 1996). The coherent superposition, prior to the OR, of the tubulin states is considered a pre-conscious process, while each instantaneous, non-computable OR is considered a proto-consciousness event. Consciousness increases significantly only when alternative conformations are part of a highly organized structure, so that OR manifestations occur in an "orchestrated" (OOR) manner. The OOR theory proposes that quantum states can be extended by tunneling, leading to entanglement with adjacent neurons via gapjunctions and the involvement of microtubule-associated proteins (C. U. M. Smith 2009).
It must be said that the OOR theory has received quite a lot of criticism, see, e.g., (Koch and Hepp, 2006; C. U. M. Smith 2009). We can further add here that it is unclear in what sense the OOR is effectively non-random and how and why the objective reduction of the wave function turns out to be orchestrated. Obviously, a fully developed theory of quantum gravity would be required to ultimately understand the measurement in MC. Hameroff and Penrose have attempted to respond in detail to the criticisms (Penrose and Hameroff 2011). However, it is worth noting here a question presented by Smith: Why would the OOR be associated with a moment of consciousness? There seems to be no obvious answer. Smith considers that Hameroff and Penrose run the risk of falling into the old post hoc ergo propter hoc fallacy (C. U. M. M. Smith 2009). However, such a fallacy does not seem to threaten a status in which we are faced with only two fundamental possibilities for nature: either classical and deterministic or quantum and indeterministic. The correlation between consciousness, non-computability and CM gives a clue to Penrose and Hameroff as to where to look for a solution.
The connection proposal between consciousness and wavefunction reduction in OOR theory is practically opposite to the initial idea developed in the early stages of CM: that a measurement is something that occurs only as result of the conscious intervention of an observer (Penrose and Hameroff 2011). Now, on the contrary, the self-organization of information in CM would be capable of generating self-awareness. Thus, according to OOR theory, self-consciousness would not be an exclusively human phenomenon, but would occur in every particle of the universe (Pregnolato 2010). Thus, Hameroff and Penrose push the correlation between consciousness and wave function reduction to the limit, turning von Neumann's stipulation on its head. In this sense, Hameroff and Penrose simply assume that consciousness emerges through the OOR at the transition from a coherent to a reduced wave function. They describe a possible new physical process involved in the emergence of consciousness-perhaps as a substrate of it-without explaining its specificity (Searle 1997). Their perspective is "bottom-up" because consciousness would emerge in nature in a way not yet understood.
In his later years of research, theoretical biologist Stuart Kauffman has embraced the quantum mind hypothesis in a slightly different way than Hameroff and Penrose, whom he credits with giving legitimacy to the physical problem of consciousness in the higher-level scientific discussion. According to Kauffman, the emergence of consciousness in a classical computational brain is not possible. Rather, the mind would have to do with a cyclically coherent brain system, which recovers coherence after having lost it. The essence of Kauffman's hypothesis is the quantum reversibility of some brain processes. The brain would be carrying out such transformations all the time (Kauffman 2009). Being open thermodynamic systems in which both energy and information can flow, cells could have evolved to have the ability to maintain almost fully coherent behavior. Kauffman imagines the training and reformation of coherent, fully percolated, electronic transport networks within the cell, thanks to changes in the ordered water molecules that connect proteins. Such percolated networks could ultimately written request reach the millisecond time scale typical of consciousness events (Kauffman 2008).
Kauffman considers his model as a variant of the mind-brain identity theory, due to what he calls "acausal mental influence". According to this interpretation, the mind would have manifestations in nature without having to act through a physical efficient cause in the brain. A partially quantum theory of consciousness, coupled with the thesis of mind-brain identity, would allow mental experiences to have consequences in actual events in the physical world without recourse to mental causes of events. The mind would act acausally on the material world through quantum decoherence, and on itself through the dynamic recoherence behavior of the single mind-brain system (Kauffman 2008; 2009). On the other hand, Kauffman admits that, even if his hypothesis were correct, the problem of the neural code and that of the unification of sensory experience(binding problem) would persist. But, even more significantly, he acknowledges that his model offers no progress at all on the fundamental question of qualia, since we do not know what it means to understand consciousness (from the point of view of the mind-brain identity theory). Nor would his theory provide an answer to the hard problem (Kauffman 2008).
A different approach to the quantum brain began in the 1960s, thanks to Umezawa and his collaborators, within the framework of quantum field theory (QFT). In these models, the brain is considered as a many-particle system continuously undergoing phase transitions that only QFT can explain. In the 1990s, Vitiello and his collaborators developed a dissipative QFT formulation of brain dynamics (Vitiello 1995; 2004; 2004; 2009; Globus 2009; Pregnolato 2010). The states of report are conceived as vacuum states of quantum fields (Atmanspacher 2011), identified as the vibrational modes of the electric dipole of water molecules. Such fields affect the neural system by developing correlations and an subject of order that can be extended to macroscopic levels (Vannini 2008). In this sense, we would be dealing with macroscopic quantum processes characterized by coherent dynamics (W. J. Freeman et al. 2012), although neurons and glia can be considered classical objects.
There would then be room for phase transitions between non-equivalent vacuum states -without the possibility of a unitary transformation between them- thanks to the interaction with the environment. Thus, two dual modes of freedom Degrees are involved, those of the brain and those of the environment. When they are adjusted, the two dualities they represent become a real unity. The unity of phenomenal consciousness would be "between-two". Vitiello locates consciousness in the state of emptiness because consciousness would be between the system and its environment; it is its "belonging together." Literally, consciousness would be a "creation of the between-two" (Vitiello 2004; Globus 2009). From the physiological perspective, the activation of a neural ensemble-initiated by external stimuli-is necessary to continuously make accessible the encoded content of the report (Atmanspacher 2011). Thus, the process of remembering involves the excitation of dipole wave quanta similar in nature to those that produce the recording of the report. When these are excited, the brain would "consciously" sense the ordered patron saint of the ground state (Vitiello 1995). Population dynamics in each sensory cortex organize the microscopic fragments so that they can give rise to meaningful knowledge - subjectively experienced as thoughts and percepts - creating macroscopic vector fields of activity that organize hundreds of millions of neurons and trillions of synapses (W. J. Freeman et al. 2012).
From a philosophical point of view, according to Vitiello, there would be no conflict between the subjectivity of first-person conscious experience and the objectivity of the external world. The latter is the necessary condition for that dissipative process of openness from which both consciousness and the unidirectional flow of time come into existence. Therefore, it would not make sense to refer to the "subject" as something preexistent to the relation with the environment. The subject would be the action, the evolving play, which never repeats itself entre-deux. This would be the meaning of the quantum entanglement between the brain and the environment (Vitiello 2004). Vitiello concludes that consciousness derives from the constant interaction of the brain with its double, which is the environment (Vannini 2008). Hence, the property that would most clearly distinguish biological intelligence from contemporary artificial intelligence is the rich contextualization of information that brains perform in constructing knowledge and meaning (Vitiello 2009; W. J. Freeman et al. 2012).
In Vitiello's dissipative quantum brain, CM can help us understand the long-range functional integration taking place in the brain. Macroscopic quantum features emerge, in the classical limit, from the CBT treatment of the brain. Moreover, Vitiello takes into account the profound consequences of his model, entering into the philosophical discussion. In particular, a particularly suggestive topic is his view on the role played by the objectivity of the environment for the emergence of consciousness, which should never be considered in isolation. However, consciousness emerges as a manifestation of the dissipative quantum dynamics of the brain (Vitiello 1995). This is the reason why consciousness is not primary, but derived from physical interactions. Also controversial is an inconsistent distinction between metal and material states, which implies the reduction of mental activity to brain activity as an underlying hypothesis (Atmanspacher 2011). For Vitiello, the continuous reorganization and restructuring of attractor spaces - due to the introduction of new vacuum states by successive stimuli - constitutes the process of contextualization through which, by differentiation with other pre-existing Structures of attractors, a "meaning" is attributed to a specific stimulus (Vitiello 2009).
As mentioned above, top-down models of quantum consciousness consider the mind to be a primary reality, with manifestations in the physical world described by CM. Probably the most specific hypothesis on how CM plays a relevant role in brain processes related to consciousness is due to Beck and Eccles (Beck and Eccles 1992). This theory makes reference letter to particular mechanisms of information transfer at synaptic junctions, where some quantum processes could be determinant for exocytosis and conscious states. Synapses have little to do with the simple on/off switches of computational devices and, regardless of what the neural correlates of consciousness are, neuroscience asserts that the places most easily affected by it are the synaptic junctions between neurons (C. U. M. M. Smith 2009; Atmanspacher 2011). Beck and Eccles' proposal has also been enriched with new hypotheses on the quantum mechanisms that trigger exocytosis (Vannini 2008).
From agreement with the theory of Beck and Eccles, preparation for exocytosis entails placing the presynaptic vesicular network in a metastable state from which the former can take place. The firing mechanism is then modeled by the quantum tunneling effect of a quasiparticle with a Degree of freedom, which must overcome the activation barrier. Thus, the model introduces into the activity of the neocortex an indeterministic selection of events controlled by the quantum probability amplitude. Mental intentions and volitions would become neurally effective by momentarily increasing the probability of vesicular emission at the thousands of synapses of each pyramidal cell. Then, the coherent coupling of a large issue of individual amplitudes of thousands of dendritic boutons would lead to the enormous variety of modes and possibilities of brain activity (Beck and Eccles 1992).
For Beck and Eccles, "psychons" would be units of consciousness that connect with each other to produce a unitary experience, the mind being an immaterial quantum field of probability (Hiley and ylkkänen 2005; Conte 2008; Vannini 2008; Conte et al. 2009). However, although the quantum effects of subject suggested by the theory might be present here, it seems unlikely to most neuroscientists that they could decisively influence the opening of fusion pores and the consequent secretion of neurotransmitters by synaptic terminals. Moreover, there remains the problem of how processes at individual synapses might come to correlate with mental activities that, as far as we know, have large ensembles of neurons as their substrate. All this has led to criticize Beck and Eccles' theory as if it were an updated version of Cartesian pineal neuropsychology (C. U. M. Smith 2001).
While most experts claim that we currently have no adequate scientific theory to explain the origin of consciousness, Stapp claims just the opposite (Stapp 1996; 2001; 2005; 2005; 2007; 2008; 2008; 2009; Schwartz et al. 2005). He does not suggest any modification to CM, but adds important interpretative extensions to the ontological framework (Atmanspacher 2011). For Stapp, there are all advantages to accepting the quantum framework . Psychology and psychiatry gain the possibility of reconciling with neuroscience regarding the mental capacity to guide actions; psycho-physics acquires a dynamic model for the interaction of mind and brain; and the Philosophy of mind is freed from the dilemma of having to choose between a theory of identity and the emergence of a mind without causal power (Stapp 2001).
Within von Neumann's conceptual framework , the observer's intervention in brain dynamics and its agreement with the person's conscious intention could be explained by the quantum Zeno effect (QZE): when a sequence of very similar measurement actions (the agent's conscious measurement choices) occurs in sufficiently rapid succession, the corresponding physical state will necessarily coincide with the sequence of states specified by the measurement results (Stapp 2007; 2008; 2009). The EZC simply maintains the brain state in the subspace of possibilities on which attention is focused by carrying out the action plan specified by the chosen questions and measurements (Stapp 2001). Thanks to EZC, a "template for action" emerges as a patron saint of physical brain activity that, when held constant for a sufficiently long time, will cause the specified action to be executed.
When seriously considering CM from the standpoint of standard interpretation, Stapp's model underscores the need to invoke the first-person account whenever a measurement is conducted. The randomness of CM is circumvented in the brain and in human actions by a learning process based on EZC. From a physical perspective, however, the hypothesis of synchronization of our conscious attentional efforts with the small decoherence times that would be expected for the brain is very controversial (see discussion in section 4). On the other hand, the question of learning should be addressed with more realistic models. In particular, criteria remain to be resolved about which responses should initially be considered as expected and in what way and why the agent would have to change freely chosen questions and measures.
In agreement initially with Stapp's perspective, Manousakis' work on the mind-brain problem entails an even deeper reinterpretation of von Neumann's quantum theory of measurement, rooted in more general philosophical ideas (Manousakis 2006; 2009). According to the ontology he postulates, consciousness is not only an essential ingredient for QM, but QM itself is grounded within an ontological framework that gives primary character to consciousness. The activities of our brain and body would be emergent consequences of conscious events. Consciousness would be the ultimate written request that simply chooses the relevant questions to be asked. Through such choices, the universe evolves in the direction prepared by the sequence of conscious events; a process that requires the division of the universe into an observed part and an "observing" part or instrument (Manousakis 2006).
The primary ontological character of consciousness advocated by Manousakis is a radical approach. While it might initially resolve issues such as the binding problem (Manousakis 2006), it gives great prominence to conscious experience, adhering to CM as the natural theory to describe what is observable in consciousness. In a sense -similar to Stapp's case- Manousakis' model is the quantum parallel of the Bayesian brain model advocated by cognitive neuroscience. The latter advocates a cascade of up-down processes, giving rise to lower-level states from higher-level causes and the wide variety of innate or learned ideas(hyperpriors) that relate to the general nature of the world (Clark 2013). But treating non-conscious reality as a mere potentiality of consciousness may mean paying a high price with respect to the ontology of the wave function and the quantum state of the system, as different states must correspond to different physical states of reality (Pusey et al. 2012). Indeed, as sample neuroscience, there are certain physical events that are imposed on consciousness.
The main criticisms of the importance of QM for neuroscience, in general, and a science of consciousness, in particular, come from the experimental field. The basic claim is that no experiment has so far demonstrated unambiguous signs of quantum manifestations in the brain. The classic argument of the proponents of QM is that quantum models fit experimental results better than ad hoc classical models. For example, it seems to make evidence for the need to account for quantum effects in the description of ion permeability between membranes. Entanglement effects in a single ion channel could lead to different rates of ionic transfer through the channel and deviations from classical predictions. While decoherence acts, the thermodynamic average over all quantum possibilities does not necessarily converge to the classical average, so that quantum entanglement could be manager of observable effects on the shape of neuronal action potentials (Naundorf et al. 2006). However, the proposed model in this case employs very few Degrees of freedom, proving too simple at the moment.
There are some promising results, not yet well established, concerning quantum effects in microtubules (as suggested by Hameroff and Penrose). On the one hand, the Biochemistry basis of depression could be correlated with a quantum nanowiring of the cytoskeleton (Pregnolato 2010); on the other hand, electrical conductivity in microtubules formed from porcine brain tubulins seems to show ballistic behaviors along different discrete helical itineraries (Sahu et al. 2013). If confirmed, such findings would point to the biological realizability of OOR (Penrose and Hameroff 2011). Similarly, the long distances over which coherent oscillations of the physical quantities involved in the brain are observed would be explained by the long range of the correlation, which would extend over the entire volume of the system as a consequence of spontaneous symmetry breaking in the dissipative quantum Vitiello brain (W. J. Freeman et al. 2011).
One of the most active fields in the experimental research of quantum effects is that of binocular rivalry. This well-known phenomenon of visual perception turns out to be a powerful tool to study the neural correlates of conscious visual experience, as the entrance signals remain constant while the "percept" oscillates between alternative representations (Conte 2008; Conte et al. 2009; Clark 2013). Conte states that the results obtained after long experimentation confirm that mental states follow a quantum patron saint during perception and cognition of ambiguous figures and also in situations of semantic conflict. There occur in these experiments, which do not deal directly with physical processes, violations of the classical Bayes formula for total probability, the occurrence of the fallacy of combination and, consequently, the need to take into account quantum interferences. According to Conte's group , instead of operating with probabilities for different alternatives, the brain would work directly with mental wave functions. Although CM is not the only theory to explain brain complexity, any reductionist approach that ignores it would be excluded by these results (Conte 2008; Conte et al. 2009).
Manousakis' framework of reference letter for integrating subjective experience and objective results can also be used to describe the probability distribution of the duration of a percept from the testimony of subjects subjected to the phenomenon of binocular rivalry. Using the formalism of a simple two-state system, model explains the observation of a marked increase in the duration of a percept in the regime of periodic interruptions of the stimulus, offering predictions about the distribution of perceptual disturbance over time. All of this derives from the fact that Manousakis' model places conscious attention higher-in the hierarchy of consciousness-than the two neural correlates stimulated in the brain. Similarly, instructing the observer to pay attention to a particular perceptual state influences and modulates the frequency of measurements; thus, when the stimulus in one eye is reinforced, the duration average of the percept in the other eye decreases. The model has some differences from a similar work by Atmanspacher, with more success in reproducing some experimental aspects (Manousakis 2009; Pothos and Busemeyer 2012).
Nevertheless, even Manousakis admits that quantum models for binocular rivalry are at best complementary to classical neuroscientific models (Manousakis 2009). At the moment, no experiment is able to validate a specific prediction of CM for the brain, as the agreement between the temporal evolution of conscious states during binocular rivalry and the predictions of the quantum formalism does not necessarily require the immediate presence of quantum effects. Recursive analyses at model of Ouroboros can yield the same results, starting from classical macroscopic features of neurons and their connections. Classical macroscopic systems can embody algorithms that mimic some quantum effects and can therefore be described to some extent by such algorithms (Thomsen 2008). In general, the current scientific understanding of various aspects of perception and action works in terms of conventional neural processing, because firing processes and synaptic processes should destroy quantum coherence (Koch and Hepp 2006).
At the beginning of the 21st century, Max Tegmark made theoretical estimates of decoherence times in the brain that ranged between 10-20 and 10-13 s. He concluded that even if there were an unknown physical process in a brain subsystem with a much longer decoherence time, as soon as that quantum subsystem interacted with neurons to give rise to a conscious experience it would lose coherence. Therefore, consciousness could not itself be quantum in nature (Tegmark 2000). Tegmark's estimates have been criticized over the last decade for several reasons: they do not include a correct dependence of decoherence times on temperature (Hagan et al. 2002; Salari et al. 2011); they employ an erroneous separation distance for possible tubulin states, underestimating decoherence times by seven orders of magnitude (Hagan et al. 2002; Penrose and Hameroff 2011); they do not take into account possible mechanisms of recoherence (Hartmann et al. 2006; Li and Paraoanu 2009) and quantum topological effects (Penrose and Hameroff 2011); they neglect dielectric permittivity, Debye layers and water ordering around microtubule bundles due to actin gelation, which can increase decoherence times up to 10-2 or 10-1 s. (Hagan et al. 2002; Abbott et al. 2008). Some authors have also pointed out that, from agreement with Tegmark's estimates for decoherence times, training of certain crystals would not be possible, which contradicts common experience. All these inconsistencies could be indicating not the transition to the classical regime, but to a CBT regime (Alfinito et al. 2001) and to the model of Vitiello's dissipative quantum brain, because of the limit of applicability of MC in favor of CBT.
More specific criticisms about the realizability of Hameroff and Penrose's OOR in the brain come from Reimers and McKemmish's group : no mechanical source of energy would suffice for the production of a strongly coherent Fröhlich condensate - as the OOR would require - in a biological medium (Reimers et al. 2009; McKemmish et al. 2009). But this question turns out to be disputed (Salari et al. 2011). London forces between the dipole states of the electron clouds in tubulins could be sufficient for quantum superposition, without the need for GTP hydrolysis or significant conformational changes (Penrose and Hameroff 2011). Penrose and Hameroff have also responded to specific criticisms by Grush and Churchland (Grush and Churchland 1995), by Tuszyński's group (Tuszyński et al. 1998) and by Koch and Hepp (Koch and Hepp 2006), whose critique of the quantum interpretation of bistable perception would strictly speaking apply only to followers of the standard MC interpretation, but not to the model OOR (Penrose and Hameroff 2011).
Hypotheses involving CM in the brain are also criticized because of the lack of correlation with the diverse regional and functional architecture of the brain. The mechanisms by which quantum phenomena interact with specific brain regions to give rise to knowledge, freedom, and consciousness would not have been precisely defined and would therefore be difficult to test experimentally (Kuljiš 2010). The pressing question is how initially quantum properties extend to the functional domain of emergent classical systems (Salari et al. 2011). For this reason, the perspective of opponents of QM in the brain can be summarized as that QM would not provide any novelty in the mechanisms studied by biological physics, nor for the resolution of the hard problem. The initially promising results cited by proponents of CM in the brain could be well understood from the point of view of standard classical physics (Abbott et al. 2008).
However, it must also be said that some recent empirical observations have begun to lend further support to the relevance of CM in biological systems. Initial difficulties in considering CM in the brain-the presence of too high a temperature, the size of biomolecules, and a noisy environment-appear to be eclipsed by quantum effects occurring at room temperature-and even at higher temperatures in inert materials (Ghosh et al. 2003)-and by the observation of macroscopic quantum effects (Kuljiš 2010; Salari et al. 2011). Researchers are beginning to understand how general and robust the phenomenon of quantum entanglement is: it can be found in macroscopic systems, persist in the thermodynamic limit for arbitrarily high temperatures, and prove crucial in explaining the behavior of large systems (Vedral 2008). Under certain circumstances, it can hold for very long time scales (Li and Paraoanu 2009). Criticisms about the relevance of QM in biology seem to be less convincing in the face of evidence for nontrivial quantum effects in biological systems (Panitchayangkoon et al. 2010; Salari et al. 2011; Lambert et al. 2012); for example, the existence of long-lived coherent quantum states in photosynthesis (Kauffman 2008), which allow quantum energy transfer for efficient light harvesting in cryptophytic seaweeds (Collini et al. 2010).
We do not yet have an answer final to the question of the empirical relevance of QM in the brain. Even its advocates summary the status saying that the scientific evidence for quantum mind is, at the moment, very weak: it turns out to be an improbable scientific hypothesis, but it cannot be definitively excluded (Kauffman 2009). There is an absence of experimental evidence and none of the quantum theories that have been put forward for the brain seem to enjoy neurological plausibility. But, at the same time, pre-MC science is not adequate to tackle the mind-brain problem (C. U. M. M. Smith 2009). All these considerations lead naturally to carry out an epistemic deepening of the phenomenon of decoherence, the physical process that, it seems, allows the transition from the quantum to the classical regime.
Quantum decoherence is currently the favorite model to explain the transition from the world of quantum possibilities to the classical world of actualized events (Zurek 2002). Decoherence theory states that when a quantum system interacts with a sufficiently large environment-which can be modeled by a huge set of quantum oscillators (Caldeira and Leggett 1983a; 1983b)-information about the relative phases of the system components becomes mixed up due to entanglement with the environment. Quantum coherence cannot then take place in the system because of this loss of information, and the classical regime-a given physical event-emerges from the cloud of possibilities. The interaction of the quantum system with its environment acts somewhat like a classical measurement device according to the standard interpretation of QM. The system is "partially measured" by its environment, hence the gradual onset of decoherence that leads the system to a classical state, a mixture of probabilities rather than superimposed quantum amplitudes. The existence of decoherence is well established experimentally and, in fact, is the major difficulty to be overcome for the construction of quantum computers. Moreover, it would be the main factor manager of the lack of relevance of QM in brain physics, which would always act as a decoherence environment for the subsystems involved in the phenomenon of consciousness.
However, how decoherence actually occurs in different physical and biological systems is only understood to a certain extent. This is a borderline question of our current knowledge (Kauffman 2008). On the one hand, as already mentioned, decoherence does not necessarily signal the emergence of the classical regime; it may also point to the emergence of the TCC regime. One has to carefully consider the physics of the system in question in order to correctly deduce what decoherence implies in each particular case (Alfinito et al. 2001). On the other hand, as Zeilinger points out, decoherence manages to get rid of quantum interference terms, but it does not explain how a particular event comes to occur (Abbott et al. 2008). In other words, what we perceive is different depending on the presence or not of decoherence, but this only destroys quantum entanglement, not the statistical character of the theory; the interpretation in terms of probabilities remains (at least at the fundamental level of description). For this reason, some experts argue that quantum indeterminacies cannot be completely eliminated in all cases. Some of them can occasionally be amplified down to the macroscopic level (Stapp 2008; Sols 2013).
Roger Penrose, among others, has carried out a thorough discussion of the problems with understanding decoherence as a complete explanation of the transition from CM to classical physics (Penrose 2004). Regardless of his own position regarding the role of CM in the mind-brain problem, Penrose sample that decoherence does not provide a consistent ontology for the reality of the world, resulting only in a useful procedure for any practical purpose . Decoherence depends on the representation one chooses for the system, so that the reduced density matrix is ultimately diagonal in a given basis but, unless it turns out to be unity (which would mean that we know nothing), it will be nondiagonal in another basis. Moreover, it does not address the problem of how the collapse of the wave function would occur in isolated systems, nor the nature of the isolation so that the environment can be ignored. Nor does it tell us what part of the system should be considered the environment, nor does it provide a limit to the size of the system that can remain subject to quantum coherence (Penrose and Hameroff 2011). Decoherence theory does not solve any of these problems, the following question remains: what is the meaning of the term "classical" in the case of a large and complex system such as the brain, which becomes a classical entity while its components (atoms and molecules) still respond to QM? (Salari et al. 2011).
Although scientists need not go any further in this direction and can limit themselves to the available empirical evidence, philosophers of science and nature may be able to draw some relevant conclusions. Even if it is true that, at present, we do not possess conclusive evidence on the relevance of CM in the brain, the simple reference letter to classical complexity as a future explanation of consciousness leads to a dead end. Since CM is the basic physical theory from which classical behavior is recovered by decoherence, decoherence itself would have to be understood in purely quantum terms. However, for the ensemble to work properly, it is necessary to resort to a different a priori treatment of the parts of the system. The latter has to be divided into a subsystem and a thermal bath (a mathematical idealization of the environment) whose Degrees of freedom are averaged. It is necessary to resort to a different, ad hoc treatment of a part of the physical system. In this sense, decoherence as an explanation of the emergence of the classical regime in the brain - and of a consciousness ultimately caused by complexity - would be an incomplete and dualistic theory.
As Paul Davis states, we are faced with the reality that CM is incomplete insofar as it offers a probabilistic description of the world and the concrete result of any observation is clearly dependent on the observer (Abbott et al. 2008), either through himself or through a measuring device created by him. Obviously, all this does not mean that reality is a pure creation of consciousness, but it does mean that consciousness is necessary for the perception of the smallest element of objective reality. Thus, the remaining possibilities for research in the mind-brain problem are: (1) either consciousness itself activates some subject decoherence, being a non-physics-derived reality, in line with the up-down theories of quantum consciousness (subsection 3.2); (2) or consciousness is the result of more subtle physical processes, not yet well understood, in line with the down-up models of quantum consciousness (subsection 3.1). Progress in neuroscience should discriminate between these two possibilities, but we can state that standard physical theory excludes any subject identity between mind and brain functioning in a classical regime.
A wrong perspective may be given when the relationship between neuroscience and CM is examined only from an empirical point of view. While such an attitude is legitimate from a strictly scientific position-see, e.g., (Koch and Hepp 2006; Thomsen 2008)-it is foolhardy to consider models based on the standard interpretation of CM as laden with mysticism or pampsychism (Vannini 2008). On the contrary, purely instrumental perspectives carefully avoid discussion of how the fundamentally quantum nature of reality comes to be made classical at the physical scales of the brain supposedly relevant to consciousness. The question is unavoidable whether all biological organisms must obey the laws of physics (Koch and Hepp 2006). Therefore, interdisciplinary reflections in the field of science and nature Philosophy can help to better understand the limits of scientific theories and to locate those enigmas to which it is worth directing energies.
Some attempts to separate the problem of consciousness from CM are based on the well-known fact of the existence of interference patterns in the relevant Degrees of freedom of the system depending on whether the information about the trajectories followed is available or not, independently of its registration in the consciousness of a human observer. For this reason, consciousness would not play an essential role in the measurement process and MC would not assign to the human observer a more special role than the one assigned to it by the classical theory. Yu and Nikolić claim that "having these two profound mysteries [consciousness and CM] separated could prove to be an important step forward in understanding each of them" (Yu and Nikolić 2011). However, while their interpretation seems to exclude the connection between wavefunction collapse and current consciousness, the subtle link between decoherence and consciousness need not be eliminated in this way. There could be prior correlations between consciousness and the experimental device for the experiment in question, producing decoherence the mere possibility of knowing the results. As Manousakis emphasizes, we construct instruments to measure quantities based on our concepts; we do not have the ability to measure unknown quantities. A particular locus of observation of consciousness originates from dividing reality into an instrument of observation and an observed system. A particular measurement consists of a question that the human mind has decided to ask through that device (Manousakis 2006).
Evidently, the connection between CM and consciousness is far from being resolved. In any case, current fundamental physics points to the fact that causal closure in physical systems, particularly in the brain, is untenable. The fact that, in CM, the choices made by human observers are not determined by the physical state of the universe means the breakdown of one of the basic properties of classical scientific theories and the inadequacy of the neurological state of the brain to determine future behavior (Stapp 2008). This raises the question of the existence of genuine top-down causality in nature. As Kauffman points out, crucially, we are dealing with a process that is not describable by laws and, at the same time, is not random. We are not trapped by the dilemma of having deterministic laws for efficient causality - including deterministic chaos - or probabilistic random descriptions of mind and brain. There seems to be a way average between pure determinism and pure randomness. Even if one resorts to decoherence, there is no a priori deterministic law for it. So far, quantum uncertainty and decoherence point to an intrinsic limit of the scientific knowledge in the form of laws, which might indicate that the measurement problem in MC has no solution within the current scientific paradigm. It is also B that - beyond the apparent regime of CM - there seem to be effects of an up-down causality in the field of conscious recognition, which casts doubt on the existence of context-independent neural correlates of consciousness (Clark 2013).
The notion of top-down causality is used to emphasize the idea that properties of higher levels of reality have influence on lower levels. This introduces the question of the existence and description of the various levels in the brain. Atmanspacher and Rotter have schematized different types of neural dynamics, covering a spectrum ranging from purely stochastic to purely deterministic descriptions. If we move from microscopic levels (subcellular, membrane-bound molecules) to mesoscopic levels (assemblies of neurons) to macroscopic levels (large networks of neuronal populations), very different stochastic and deterministic models are relevant for the description. Moreover, there is no clear threshold at which neuronal dynamics is deterministic or stochastic, nor are there universal rules for determining how the transition from one dynamic to the other occurs as the level is changed. It is even possible to find mathematical transformations to switch from one subject description to another. At summary, the delicate relations between randomness and determinacy cast doubt on the possibilities of inferring ontologically valid statements in this respect from neurodynamic descriptions. Moreover, a strict reduction from higher to lower levels of description fails in this context. The description of the lower level provides necessary but not sufficient conditions for the description of the higher level. The characteristics of the higher level do not result as a necessary logical consequence from the descriptions of the lower levels, nor can they be rigorously derived from the latter alone. However, sufficient conditions for the derivation of higher level features can be implemented by identifying contexts that reflect the particular subject contingency that occurs in such a status (Atmanspacher and Rotter 2008). This procedure cannot originate from the lower levels, remaining irreducible.
There is thus an irreducibility of higher level contexts, which play the role of constraints acting "downward". None of the bottom-up or top-down versions of causality are sufficient to describe causality in the mind-brain problem. The existence of correlations between the brain and the mind is peacefully admitted, but asserting which is cause and which is effect is absolutely hypothetical insofar as the model of causality remains unspecified and there is no available theoretical background for the corresponding interpretation. In particular, the assertion of an ontic determinism in neural dynamics cannot be defended on the basis of the currently established knowledge ; any implication one wishes to draw from there runs the risk of being fundamentally flawed. Thus, reductionism is not only simplistic but, in general, false. This becomes even more manifest when one transitions from the different levels of brain description to those of mind and behavior (Atmanspacher and Rotter 2008). Kuljiš has also pointed out the challenge implied - in terms of an interdisciplinary integration in search of a coherent understanding of the problem - by the wealth of information present in the multitude of conceptually decoupled physical scales and domains in contemporary neuroscience. This task to be solved includes the CM hypothesis in the brain, as it represents the minimum level to be considered in a comprehensive and unitary understanding of brain functioning (Kuljiš 2010).
These reflections show the implicit need to resort to a higher anthropological level when trying to understand physical reality and, in particular, the mind-brain relationship. The problem of consciousness is a manifestation of a more fundamental gnoseological problem in CM, which should be approached with attention to the underlying philosophical implications. Physical laws are quantum laws that, in some ill-defined limit, become classical. Therefore, the inevitable question is how this happens in the brain as well. The pure resource to decoherence is irrelevant at this point of the discussion, since the definition of the system and the environment has to be made a priori, without being able to be strictly derived from the theory. In other words, to cognitively access physical reality, and in particular the physical reality of the brain, requires the action of a higher anthropological level. Such a level is not derivable from any scientific law, but a condition of possibility of science itself. We average the Degrees of freedom of the thermal bath because we know a priori the subject of information we are looking for in the system. The anthropological level, analogously to any other irreducible level, introduces novelty into the world by doing science and interpreting its results as truly informative knowledge . As far as we know, the conscious observer provides the highest level of information processing that occurs in the universe. It introduces specific constraints that allow an unambiguous transition from lower to higher levels.
Consciousness introduces into the world human information that can be stored in the objective quantum states of the universe, according to the laws of QM. Consciousness does not create reality, but determines it to a certain extent. It allows a deeper knowledge of a nature formed by different intertwined levels, with different epistemic properties, which can only be known by a being with a cognitive power similar to that of the higher level. Some scientists claim that classical complexity could come to explain the emergence of phenomena such as thoughts and freedom (Tegmark 2000), but the language of complexity itself is no different from the language of statistical physics. However, its interpretation - mediated by the anthropological level - may come to add something more. Such an interpretation is strictly non-materialistic, for there is no interpretation in purely material nature (Searle 1997). In this sense, human consciousness and science are totally related, the latter constituting an exploration of reality different from that which non-human animals or inert beings can perform. As Hagan rightly remarks, by treating the phenomenon of consciousness or the subject as merely another object of study, no explanation is given as to why its Degrees of freedom should have a subjective connotation or how they come to be associated with each other in a way that does not depend on the arbitrary assignment of an observer. While the "object" is simply the name assigned to a subsystem of the whole, the "subject" is not an arbitrary product of how someone chooses to analyze a system. The existence of an object of study is a relative fact, dependent on the analysis, but the existence of the subject is absolute and its determination is a fact that itself needs explanation (Hagan et al. 2002). It seems, therefore, that the philosophical framework of CM is relevant in neuroscience to the mind-brain problem not so much because it provides a fundamental randomness as opposed to determinism, but because it postulates an irreducible influence of the subject's conscious access to the description of reality.
CM manifests our inability to understand human consciousness from a purely objective approach. In addition to other well-known problems, conventional theories of mind-brain identity rely crucially on decoherence processes to explain the transition from the quantum to the classical world. However, their theoretical implementation requires a subjective choice of system and environment whose Degrees of freedom has to be suppressed. As a consequence, identity theories of mind and brain, which rely implicitly or explicitly on decoherence, are insufficient, as they hide in their foundations what they are trying to explain.
The models that attempt to introduce CM as framework relevant to neuroscience are diverse: some simply apply the quantum formalism without entering into the discussion of the underlying physical processes; others - the bottom-up theories of quantum consciousness - consider consciousness as an emergent property of quantum nature, yet to be determined; finally, the top-down theories of quantum consciousness tend to be dualistic, advocating a primary role of consciousness in nature without determining the mode of interaction with the rest of reality. So far, experimental evidence has been non-existent or, at best, inconclusive, with binocular rivalry being one of the most promising fields from the empirical point of view.
In spite of being at a status impasse, what the models studied have in common is the understanding that the problem of the measurement of CM is intimately linked to the hard problem of consciousness. It is highly unlikely that we will make progress in solving one of the problems without making progress in solving the other. There is a literature that regards this link as an example of the fallacy: "I don't understand A, I don't understand B, therefore A and B must be related"; however there are a number of arguments that show why such a fallacy would have no place here. Since decoherence is a procedure with epistemic constraints and prescriptions, we cannot hope to understand the ontological emergence of consciousness without understanding the paradox of measurement in CM. The latter must play a relevant role in the whole problem and is not likely to have the last word, since there are also powerful philosophical reasons that defend an understanding of human consciousness beyond natural science (Arana 2015).
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