How Quantum Theory Attempts to Explain Human Consciousness
Summary of Studied Schemes :
Coupling of Microtubule/Tubulin Conformation States to Quantum Events within the Brain; Gravitation-Induced Objective Quantum Reduction of Tubulin States Generating Consciousness
Ordered Neuronal Assemblies arsing from Stochastic Single Neurons by Quantum Stochastic Resonance;Volition Enhanced Quantum Process in Exocytosis
Ordered Neuronal Assemblies through Symmetry Breaking; Encoded Memory = Coherent Neuronal Assemblies in Ground State while Memory Recollection = Excitation of Ground State; Sense of Time = Ground State Dissipation-Environment Entanglement
Reductions of Superposition Neuronal Assemblies States = Conscious Acts; Quantum Zeno-Type Effects Protracting Lifetime of Neuronal Assemblies = Mental Efforts
Time-Entangled Mind-Matter Emergent from the Underlying Neutral Reality of Unconscious Archetypes
Quantum theory is relevant to human consciousness because collapse-type quantum events (the transition of a quantum state to an eigenstate bj of the measured observable B with a certain probability) are intrinsically random, and this randomness is primary (ontic) rather than merely due to ignorance or missing information (epistemic).This ontic randomness, in contrast to deterministic classical physics, can more suitably account for conscious mental acts influencing brain behavior, manifested outward as volition or free will.
The relationship between the brain and the mind can be explained by two distinctive philosophical approaches :
All mental states and properties can be reduced to the material domain (materialism) or even to physics (physicalism). These schemes focuses on qunatum reduction/wave collapse.
However at our present level of knowledge, it might be premature to establish firm causal relations between mental states and the material brain. Furthermore, the mind could be an irreducible existent "emergent" in a complex system. This emergence theory is difficult to repudiate if the material brain is not necessary or not sufficient to explore and understand the mind.
There are also qualia (immediate conscious experiences) arguments, which emphasize the impossibility for materialist accounts to properly incorporate the quality of the subjective experience of a mental state, the “what it is like” feeling. For example, it would be difficult to include notions of temporal present and "nowness" in a physical description.
B) Dualistic Approaches
Mental and material domains of reality are aspects, or manifestations, of one underlying reality in which mind and matter are unseparated. These schemes focus on quantum entanglement, rather than the direct interaction in quantum reduction/wave collapse, to understand correlations between mental and material domains.
These approaches also consider the causal influences of mental states upon materialistic brain states, though indirectly, via a third category, an underlying psychophysically neutral reality.
The human brain is a complex physical system of neurological structures. Simultaneously it is a complex mental system in a sequence of many different conscious, intentional mental states forming a trajectory representing the stream of consciousness.
The physical brain is closely correlated with human consciousness since particular brain areas are activated during particular mental activities.Stable states are distinguished by a residence time longer than that of metastable or unstable states. If a mental state is stable with respect to perturbations, it activates a mental representation encoding a content that is consciously perceived.
The physical neurological structures is describable at three neurophysiologic levels:
Level 1 : Neuronal assemblies
Neuronal assemblies are ensembles of several thousands of coupled neurons. The connectivities, or couplings, among those neurons form an assembly confined with respect to its environment where connectivities are weaker than within the assembly.
The neural correlate of a mental representation is activated if the neurons forming the assembly operate more actively, e.g., produce higher firing rates, than in their default mode.
In order to achieve a stable operation of an activated neuronal assembly, there must be a subtle balance between inhibitory and excitatory connections among neurons. It has been found that the firing activity is a non-monotonic transfer function with a maximal output at intermediate input.
Current models of neuronal assemblies are mostly formulated in a classical way, without resorting to quantum theory.
Level 2 : Single Neurons and Synapses
There are two types of synapses. At electrical synapses, the current generated by the action potential at the presynaptic neuron flows directly into the postsynaptic cell, which is physically connected to the presynaptic terminal by a gap junction. A signal is propagated in this process.
At chemical synapses, there is a cleft between pre- and postsynaptic cell. In a release process called exocytosis, a chemical transmitter (glutamate) is released at the presynaptic terminal. The transmitter diffuses across the synaptic cleft and binds to receptors at the postsynaptic membrane, thus opening an ion channel. A signal is also propagated in this process.
Anaesthetic agents blocking a specific type of receptors, so-called NMDA receptors in chemical synapses, will consequently lead to a loss of consciousness. The specific plasticity of NMDA receptors is a necessary condition for the formation of extended stable neuronal assemblies correlated to (higher-order) mental representations identified with conscious states.
Level 3 : Microtubuli and Tubulin
The cytoskeleton, made up of hollow fibers which serve as a skeletal system for living cells, is essential for various transport processes within neurons. The cytoskeleton of single neurons consists of protein networks essentially made up of two kinds of structures, neurofilaments and microtubuli. Microtubuli are long polymers usually constructed of 13 longitudinal α and β-tubulin dimers i.e. a large assembly of two (di-) polypeptide chains arranged in a tubular array with an outside diameter of about 25 nm.
Microtubules have the ability to shift through various formations which is what enables a cell to undergo mitosis or to regulate intracellular transport. Its constituent tubulin, a globular protein that polymerizes into long chains or filaments that form microtubules, is flexible in structure. The formation-shifting of microtubules is made possible by this flexibility of tubulin.
Quantum Explanation of Human Consciousness
Several schemes use quantum theory in different ways to explain human consciousness. They refer to processes at the three different neurophysiological levels.
1. Consciousness = Orchestrated Objective Reduction of Quantum Tubulin States
In this speculative but specific theory, physicist Penrose and anaesthesiologist Hameroff assume that tubulin states are dependent on quantum events, so that quantum coherence among different tubulins is possible; gravitation-induced collapse of such coherent tubulin states corresponds to elementary acts of consciousness.
Gravitation-Induced Objective Quantum Reduction
The quantum theory foundatioin for this scheme, quantum gravity, the ultimate unification of all physical interactions, has yet to be developed. Penrose put forth his conjecture regarding gravitation-induced objective quantum reduction based on two considerations :
a) A valid formulation of quantum state reduction must faithfully describe an objective physical process, viz., an objective reduction. A quantum wave function “self-collapse”should replace the collapse or reduction of the wavefunction caused by observation (with an observer) or environmental entanglement. Since present-day quantum theory does not contain such a picture, gravitational effects not currently covered by quantum theory should play a role in state reduction.
b) Since elementary acts of consciousness are non-algorithmic, i.e., non-computable, the emergence of a conscious act should be a process which cannot be described algorithmically, hence cannot be computed. Although the processes of state reduction in standard quantum theory is random and indeterministic, these probabilistic and stochastic processes can be standardly implemented on a computer, hence they are definitely computable. In contrast, the processes of state reduction in quantum gravity would be not only random, but genuinely non-computable. Penrose himself has sketched some ideas concerning these non-algorithmic features of quantum gravity.
Penrose therefore suggests that in quantum gravity superpositioned states each have their own space-time geometries. When the degree of coherent mass-energy difference leads to sufficient separation of space-time geometry, the system must choose and decay (reduce/collapse) to a single universe state. In this way, a transient superposition of slightly differing space-time geometries persists until an abrupt quantum self-collapse occurs.
Coupling of Microtubule/Tubulin Conformation States to Quantum Events within the Brain
Special locations are required to ensure that quantum states can live long enough to become reduced by gravitational influence rather than by interactions with the warm and wet environment within the brain. Hameroff suggests microtubules suitable for quantum effects considering their particular characteristics such as their crystal-like lattice structure, hollow inner core, organization of cell function and capacity for information processing.
In this scheme it is envisaged that conformational states of tubulins are coupled to internal quantum events, and cooperatively interact with other tubulins. It is assumed that macroscopic coherent superposition of quantum-coupled tubulin conformational states occurs throughout significant brain volumes and provides the global binding essential to consciousness.
Gravitation-Induced Objective Quantum Reduction Generating Consciousness
This scheme equates the emergence of the microtubule quantum coherence with pre-conscious processing which grows for up to 500 milliseconds until the mass-energy difference among the separated states of tubulins reaches a threshold related to quantum gravity. Then gravitation-induced objective quantum reduction results in particular patterns of microtubule-tubulin conformational states that regulate neuronal activities including synaptic functions. This quantum reduction event corresponds to elementary acts of consciousness.
Possibilities and probabilities for post-reduction tubulin states are influenced by factors including attachments of microtubule-associated proteins (MAPs) acting as "nodes” which tune and "orchestrate”the quantum oscillations (hence the name "orchestrated objective reduction"). The scheme has calculated an estimate for the number of tubulins (and neurons) whose coherence for relevant time periods (e.g. 500 milliseconds) will elicit orchestrated objective reduction.
Thus this theory provides a connection among 1) pre-conscious to conscious transition, 2) fundamental space-time notions, 3) non-computability, and 4) binding of various (time scale and spatial) reductions into an instantaneous event ("conscious now").
2. Mental Intentions Influencing Quantum Mechanical Process in Exocytosis
This scheme offers empirically concrete and theoretically detailed biophysical explanation of changes in brain states from a quantum theoretical point of view.
Quantum Tunnelling of Electrons in Exocytosis
The release of transmitters in the presynaptic terminal in the process of exocytosis is triggered by an arriving nerve impulse with some small probability, thus describable in a statistical way using quantum mechanics.
Beck and Eccles propose that the trigger can be concretely understood in terms of electron transfer between biomolecules, in quantum tunneling processes of two-state quasi-particles, resulting in state collapses/reduction. It yields a probability of exocytosis in the range between 0 and 0.7, in agreement with empirical observations.
Ordered Neuronal Assemblies arsing from Stochastic Single Neurons by Quantum Stochastic Resonance
Processes at single synapses cannot be simply correlated to mental activity, whose neural correlates are coherent assemblies of neurons. Plausibly, prima facie uncorrelated random processes at individual synapses would result in a stochastic network of neurons.
There are indicated possibilities for achieving ordered patterns at the level of neuronal assemblies from fundamentally random synaptic processes by quantum stochastic resonance.
Volition Enhanced Exocytosis
The fundamentally indeterministic nature of individual quantum state collapses offers room for the influence of mental powers on brain states. Beck and Eccles consider that “mental intention (volition) becomes neurally effective by momentarily increasing the probability of exocytosis.
This scheme has not (yet) explained how the activity of single synapses enters the dynamics of neural assemblies, and it leaves mental causation of quantum processes as a mere claim.
3. Ordered Neuronal Assemblies through Symmetry Breaking; Encoded Memory = Coherent Neuronal Assemblies in Ground State while Memory Recollection = Excitation of Ground State; Sense of Time = Ground State Dissipation-Environment Entanglement
Ricciardi and Umezawa use quantum field theory to describe brain states, pointing to the emergence of classical activity in neuronal assemblies on the basis of symmetry breakings in a quantum field theoretical framework.
Collective/Ordered Neuronal Assemblies through Symmetry Breaking
Spontaneous symmetry breaking occurs when the ground state of a system is not invariant under the full group of transformations providing the conservation laws for the system. If symmetry breaks down, collective modes (Nambu-Goldstone boson modes) are generated which propagate over the system and introduce long-range correlations in it. These correlations are responsible for the emergence of dynamically ordered patterns.
Encoded Memory = Coherent Neuronal Assemblies in Ground State while Memory Recollection = Excitation of Ground State
This theory addresses the brain as a many-particle system as a whole, where the “particles” are neurons. The coherent neuronal assemblies directly correlates with mental activity such as memory states are regarded as vacuum/ground states.
The activation of a neuronal assembly is necessary to make the encoded content consciously accessible. This activation is considered to be initiated by external stimuli. Their activation leads to excited states with a finite lifetime and enables a conscious recollection of the content encoded in the vacuum/ground state.
Limited Memory due to Dissipation and Dissipation-Environment Entanglement = Sense of Time
The system-environment interaction causes a doubling of the collective modes of the system in its environment. This yields infinitely many differently coded vacuum states, offering the possibility of many memory contents without overprinting. Dissipation leads to finite lifetimes of the vacuum states, thus representing temporally limited rather than unlimited memory. Moreover, dissipation generates a genuine arrow of time for the system, and its interaction with the environment induces entanglement, giving rise to a sense of temporal correlation with events.
Potential neurobiologically relevant classical observables such as electric and magnetic field amplitudes or neurotransmitter concentration in neurons, glia cells and other physiological units in the brain are currently being examined in relation to this theory. However, the theory treats reducibility of mental activity to brain activity as an underlying assumption. A clear conceptual distinction between brain states and mental states has been missing so far. This suggests a vague inclination toward a dual-aspect approach.
4. Reductions of Superposition Neuronal Assemblies States = Conscious Acts;
Quantum Zeno-Type Effects Protracting Lifetime of Neuronal Assemblies = Mental Efforts
In the Copenhagen interpretation of quantum mechanics the actual is related to a measured event while the potential, of a tendency, relates to the situation before measurement, which expresses the idea of a reality independent of measurement. Immediately after its actualization, each event holds the tendency for the impending actualization of another, subsequent actual event.
Intentional Acts/Free Will Intrinsically Correlated with Reduction of Superposition States of Neuronal Assemblies
In this scheme, Stapp considers the mental and physical outcomes of the actual occasions as two matching i.e. correlated aspects of the same reality. it locates the interface between observed and observing system in the observer's brain and attaches to each actual event an experiential aspect. The latter is called the feel of this event, which is the aspect of the actual event that gives it its status as an intrinsic actuality.
Each conscious experience has as its physical counterpart a quantum state reduction of superposition states of neuronal assemblies, which is the neural correlate of that conscious experience. This pattern of activity may encode an intention and, thus, represent a “template for action”. This intentional decision for an action, preceding the action itself, is “free will”.
Quantum Zeno-Type Effects Protracting Lifetime of Neuronal Assemblies = Mental Efforts
Mental effort, i.e. attention devoted to such intentional acts can protract the lifetime of the neuronal assemblies that represent the templates for action due to quantum Zeno-type effects, i.e. the suppression of unitary time evolution caused by quantum decoherence in quantum systems provided by a variety of sources: measurement, interactions with the environment, stochastic fields, and so on.
This scheme has not yet worked out empirically and precisely how quantum superpositions and their collapses occur in neural correlates of conscious events.
5. Time-Entangled Mind-Matter Emergent from the Underlying Neutral Reality of Unconscious Archetypes
Emergence of Physical Matter and Conscious Mind from Archetypes in Collective Unconscious
In this scheme, Pauli and Jung consider that there is a fundamentally holistic, psychophysically neutral level of reality, the archetypes in the collective unconscious, from which "synchronistic" correlated mental and material domains emerge. Similarly Bohm and Hiley refer to an implicate order which unfolds into the different explicate domains of the mental and the material.
Thus the scheme proposes a dualistic mind-matter entanglement instead of a reductionistic quantum reduction/collapse.
Mind-Matter Causation due to Ordering Operation of Archetype
In Jung's depth psychological conceptions, conscious and unconscious domains are connected by a process of emergence of conscious mental states from the unconscious, analogous to physical measurement in quantum theory. The unconscious has a collective component, unseparated between individuals and consisting of the psychophysically neutral archetypes. They are regarded as constituting the psychophysically neutral level covering both the collective unconscious and the holistic reality of quantum theory. Mind and matter causation is expressed by the ordering operation of archetypes in the collective unconscious. These "synchronistic" correlations have been applied to psychosomatic relationships.
Symmetry Breaking of the Timeless Neutral Reality Gives Rise to Time-Entangled Mental Tensed Time and Physical Tenseless Time
Primas has proposed that the distinction of mental and material domains originates from the distinction between two different modes of time:
1. tensed (mental) time, including nowness,
2. tenseless (physical) time, viewed as an external parameter.
These two concepts of time is implied by a symmetry breaking of a timeless level of the underlying psychophysically neutral reality. The tensed time of the mental domain is quantum-correlated with the parameter time of physics via “time-entanglement”.
Primas approach leads to panpsychism or panexperientialism because in the limit of a universal symmetry breaking at the psychophysically neutral level, every system has both a mental and a material aspect. The special case of human consciousness within the mental domain as a whole might be regarded as special as its material correlate, the brain, within the material domain as a whole.
"Quantum Approaches to Consciousness", Stanford Encyclopedia of Philosophy,2011
1st Draft by Stewart Yeung on 24 Feb 2012