The Central Enigma of Consciousness
Chris King
Mathematics Department,
University of Auckland
© 3-11-08 - 20-8-19
For significant updates, follow @dhushara on Twitter
Abstract: The nature and
physical basis of consciousness remains the central enigma of the scientific
description of reality in the third millennium. This paper seeks to examine the
phenomenal nature of consciousness and elucidate a possible biophysical basis
for its existence, in terms of a form of quantum anticipation based on
entangled states driven by chaotic sensitivity of global brain states during
decision-making processes.
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See my more recent article Space, Time and Consciousness Mar 2014 for a more recent perspective on emerging research in the same area.
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0 Contents
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1 The Enigmatic Theatre of Conscious Experience
2 A Dynamic View of the Conscious Brain
3 Edge of Chaos, Self-organized Criticality and Fractal Sensitivity
4 Sensory Transduction and Subjective Experience
5 Computational Intractability, Classical Chaos and Quantum Uncertainty
6 The Evolution of Chaotic Sensitivity and the Emergence of Consciousness
7 Quantum Entanglement and the Transactional Interpretation
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Other Neuroscience Research Papers:
Entheogens, Conscious Brain and Existential Reality Jun 2012 psychedelics, neuroreceptors and consciousness.
Review: Cutting through the Enigma of Consciousness Nov 2010
Research Report: The Cosmological Foundations of Consciousness Jan 2011
Sexual Paradox in the Conscious Brain, 2003 with work on mirror neurons and sexual differences.
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1 The Enigmatic Theatre of
Conscious Experience
The
term consciousness itself is enigmatic.
Both ÔmindÕ and ÔconsciousnessÕ present a varied array of associated
words and concepts, which we need to clarify, to even begin to close in on the
central enigma, which the terms present to us. Mind conjures up a plethora of concepts from minding i.e.
emotional caring, or objecting, through the rational mind of thought and language
based reasoning, mindfulness or focused concentration, to absent-, clear- or
small- mindedness to the mindless blunders many of us consciously make, despite
ourselves. Consciousness can mean everything from the root capacity to have
subjective experiences at all, through awake alertness, as opposed to the
slumber, or coma, of unconsciousness, through the fuzzy boundary between
subconscious or unconscious processing that accompanies conscious cognition, to
the restrictive idea of self-consciousness, as knowing that you know - Òa conscious state is one which has a
higher-order accompanying thought which is about
the state in questionÓ [1].
Wikipedia
[2],
[3] has the following introductory
descriptions, chosen because they are a product of a social process of
consensual agreement as to their meaning and content:
ÒMind
collectively refers to the aspects of intellect and consciousness manifested as
combinations of thought, perception, memory, emotion, will and imagination;
mind is the stream of consciousness. It includes all of the brain's conscious
processes. This denotation sometimes includes, in certain contexts, the working
of the human unconscious or the conscious thoughts of animals. "Mind"
is often used to refer especially to the thought processes of reason.Ó
ÒConsciousness
has been defined loosely as a constellation of attributes of mind such as
subjectivity, self-awareness, sentience, and the ability to perceive a
relationship between oneself and one's environment. It has been defined from a
more biological and causal perspective as the act of autonomously modulating
attentional and computational effort, usually with the goal of obtaining,
retaining, or maximizing specific parameters (food, a safe environment, family,
mates). Consciousness may involve thoughts, sensations, perceptions, moods, emotions,
dreams, and an awareness of self, although not necessarily any particular one
or combination of these.Ó
Although
these contain a constellation of meanings, in which mind is sometimes focused
on the attributes of reasoned, or even language-based thought, and
consciousness is sometimes given the more restrictive meaning of
self-awareness, both contain a central arena of subjectivity and sentience,
while conceding that the boundaries between consciousness and the sub- or
unconscious may be fuzzy, both in varied brain states, from waking thought to
sleep and coma, and in complex autonomous processes, which go on below the
level of immediate awareness, during activities like driving a car.
The
central enigma we are referring to is not self-consciousness, but subjective
consciousness – the capacity of a conscious sentient being to have a
subjective experience of the existential condition, both of the everyday world,
and of dream, memory and reflection [4],
hallucination, psychedelic reverie, and other forms of internal subjective
experience, not necessarily correlated with the immediate events of the
physical world.
In
the face of the apparent causality of the Laplacian universe, many 20th
century philosophers assigned to consciousness the orphan status of an epiphenomenon,
a mere reflection of physical reality which could have no influence upon it.
Some, such as Gilbert Ryle [5], who coined
the term Ôthe ghost in the machineÕ, went further, attempting to deconstruct
the dualistic notion of mind altogether, as a form of false reasoning, claiming
Òthat the idea of Mind as an independent entity, inhabiting and governing the
body, should be rejected as a redundant piece of literalism carried over from
the era before the biological sciences became established. The proper function
of Mind-body language, he suggests, is to describe how higher organisms such as
humans demonstrate resourcefulness, strategy, the ability to abstract and
hypothesize and so on from the evidences of their behaviourÓ [6].
Derived
from the dualistic cosmology of Rene Descartes, this subjective arena is
frequently referred to as the ÒCartesian theatreÓ, sometimes constructively, as
in Barrs [7],
[8],
who describes the theatre of the conscious in terms of working memory and its
associated backdrops, but other times in somewhat disparaging terms as in
Dennett [9],
who, rather than explaining consciousness, as he claims, replaces it with a
Ômultiple drafts modelÕ, more representative of the publishing industry, than
either the conscious mind, or the sentient brain.
Some
of these criticisms arise from the practical difficulties of defining the
borders of consciousness and the difficulty of finding the actual mechanisms
for generating the Ôinternal model of subjective realityÕ in terms of brain
centers and their electrochemical dynamics, in the absence of clear evidence
characterizing which brain states other than general focused global activity
are responsible for consciousness, and as a result of the binding problem - how
and where the disparate components of brain processing are all brought together
in the hypothetical ÔCartesian theatreÕ of the mind. Some of these problems are
misplaced because they are falsely identifying brain and mind states. For example, the Ôbinding problemÕ of
brain dynamics may be resolved in practical terms through the phase coherence
of excitations that are related, to form resonant neural circuits,
differentiating them from the incoherent noise of the background, even though
there is no specific brain centre as such where consciousness is generated.
At
issue is a fundamental frame of subjective reference, and a confusion on the
part of brain researchers and philosophers alike, between the physical world,
and our representation of it in the so-called Ôinternal model of realityÕ, which
tends to become finessed in the dialectics of discourse on the problem.
The
veridical reality is that from birth to death each of us is a subjective
conscious observer of the existential condition. All our experiences of the
physical universe are without exception subjective conscious impressions, which
only we as individual subjective observers have access to. Ultimately all data
and scientific observations of the universe likewise achieve validation through
the subjective conscious experience of the researchers and those who read their
papers and witness their results.
Far
from being the fundamental components of veridical reality, the physical
universe and all the constructs applied to it, from wave-particles through
atoms and molecules, to complex biological systems such as the sentient brain
and all our experiences of the everyday world around us are entirely, and
without exception, purely and completely, abstract models of subjective
conscious impressions, knitted together by a consensual agreement between
subjective perceivers - that the table before us is solid and made of wood,
plastic, or metal, as the case may be, and that our impressions of the world,
from the lemon, or coffee cup on the table, to the horizon upon which we gaze,
from a lonely hill top, looking out to sea, or the stars and galaxies we
perceive in the sky, and entertain the humbling specters of an eventual demise
in the heat death or big crunch, according to cosmological theories of the
time.
Subjective
consciousness is thus the primary veridical conduit of existential reality, and
the phenomena of the objective world, for all the convincing lessons that we
are biological organisms which bleed if we are cut, and lose consciousness if
we slumber, or are concussed, are consensual stabilities of our subjective
consciousness. This remains true, notwithstanding our obvious dependence on our
brain states, and the fact that some of the most bizarre and interesting states
of altered consciousness arise from psychoactive molecules, which mimic
neurotransmitters, or transport processes affecting synapses and thus radically
altering brain states.
However,
based on the consistency of the scientific description of the physical universe
and our part in it, as biological organisms dependent on our functioning brains
to survive, this veridical logic has tended to become reversed, on the basis of
the inaccessibility of subjective experiences to objective experimental testing
and replication, so that consciousness has either been relegated to an epiphenomenon,
merely reflecting, but not influencing, physical processes, e.g. in the brain,
or banished to the wilderness, as Ôna•ve or imaginaryÕ concepts not well
founded in the domain of philosophical or scientific discourse.
Put
in its completion, the relationship between consciousness and physical reality,
rather than being either an epiphenomenon, or mere identity, or a fully divided
Cartesian duality has characteristics more of the complementarity we see
between the wave and particle aspects of the quantum world, in which a quantum
can manifest wave, or particle natures, but not both at the same time, and in
which the two aspects are also qualitatively symmetry-broken, one being
discrete and the other continuous. It is this type of complementarity that Lao
Tsu called a Tao or ÔwayÕ of nature, and subjective consciousness and the
objective physical universe clearly have just such a qualitative
complementarity existentially.
Fig
1: BaarsÕ description of the Cartesian Theatre of consciousness and its
ÔplayersÕ in terms of functional working memory processes.
The
nature of this complementarity and its fundamentality in the light of attempts
on the part of functionalists to finesse consciousness to be merely an aspect
of the attention process, or certain classes of excitation, such as those in
the gamma range of the EEG (30-60 Hz), have been highlighted in David ChalmersÕ
[10]
enunciation of the so-called ÒHard ProblemÓ in consciousness research, -
Òexplaining why we have qualitative phenomenal experiences'. It is contrasted
with the Òeasy problemsÓ of explaining the ability to discriminate, integrate
information, report mental states, focus attention, etc. Easy problems are easy
because all that is required for their solution is to specify a mechanism that can
perform the functionÓ [11]. For example Crick and Koch [12]
identify conscious states accompanying attentive processes with higher
frequency electroencephalogram (eeg) signals in the gamma range. Defining
consciousness as a functional process associated with attention and/or working
memory is addressing an ÔeasyÕ problem in consciousness research. The dilemma
of the ÔhardÕ problem implies that no purely objective mechanism can suffice to
explain subjective consciousness as a phenomenon in its own right.
BaarsÕ
approach suggests that consciousness is associated with the whole brain in
integrated correlated activity and is thus a property of the brain as a whole
functioning entity rather than a product of some specific area, or system, such
as the supplementary motor cortex [13],
[14],
[15].
Furthermore, the approach rather neatly identifies the distinction between
unconscious processing and conscious experience in terms of whether the dynamic
is confined to local or regional activity or is part of an integrated coherent
global response. It is also consistent with there being broadly only one
dominant stream of conscious thought and experience at a given time, as diverse
forms of local processing gives way to an integrated global response. A series
of experiments, many by teams working with Stanislas Dehaene, involving
perceptual masking of brief stimuli to inhibit their entry into conscious
perception [16],
[17],
[18],
[19],
[20],
[21],
[22],
studies of pathological conditions such as multiple sclerosis [23],
[24],
and brief episodes in which direct cortical electrodes are being used during
operations for intractable epilepsy [25] have
recently tended to confirm the overall features of BaarsÕ model of
consciousness founded on the global work space [26],
[27],
[28].
Two opposing global attention systems have been
identified [29],
one the dorsal attention network deals with focal attention in the global
workspace and is bilateral, connecting areas such as the frontal eye fields to
parietal and other areas. Complementing this is the ventral attention network
whose role is to bring in salient stimuli, important to the subject, from the
periphery. Intriguingly this has lateralized activity in the right cortex,
complementing the left hemisphere regions traditionally associated with
language, lending support to the above model of lateralization.
A third system, the Ôdefault networkÕ [30], is
associated with mental activity not grounded to any immediate activity. It was
first discovered because there were areas with enigmatic deactivation in a
variety of brain studies, such as attending a sensory task. When subjects were
then tested just resting or daydreaming the same areas were activated. The
default circuit is activated by processes as diverse as autobiographical
memory, envisioning the future, theory of mind, moral decision-making [31],
[32], [33], as
well as mind-wandering activities such as daydreaming and worrying. The default
circuit is believed to be a state in which we aid our survival strategies by
using Ôdown timeÕ to rehearse impending situations of significance to enhance
our ability to cope with them successfully. It has also been associated with
improved creative thinking over focussed working memory, for example in solving
counter-intuitive puzzles [34]. One can loosely
identify the default network with the process of daydreaming, reminiscence,
worrying and idle thought, but in these terms it looks clearly like a
manifestation of global work space in action and hence provides another view on
the global mechanisms being brought into play in conscious experience [35].
Intriguingly recent brain scan studies have shown the
cortical regions excited by looking into the future to be virtually identical
to those involved in memorizing the past [36],
[37],
[38]
and damage to episodic memory structures also prevents subjects being able to
envisage future events [39], suggesting
the way the brain is going about this is in a sense Ôtime symmetricÕ.
Another cortical system that may be critical for our self-consciousness consists of the anterior insula cortex and anterior cingulate cortex which appear to be motor and sensory areas integrating our interoceptive bodily and emotional awareness with our sense of rapid time-framing of the immediate present. Both of these areas contain unique giant von Economo neurons, which occur only in higher apes and a few isolated large-brained species including elephants and whales, which may enable rapid central integration of the sense of personal identity. Significantly these species tend to be those that can recognize themselves in a reflection [40], [41], [42], [43].
However,
while these systems integrate the notion of conscious experience neatly in with
the coordinated activity of the whole brain, they still donÕt explain how the
brain generates subjective conscious experience, or indeed what the subjective
aspect provides that has led to it being selected by evolutionary change.
Completing
the enigma of consciousness is the thorny spectre of Ôfree-willÕ, upon which
all concepts of law and personal accountability hinge, as well as the
assumptions of virtually every religious tradition. Although it is possible to
couch questions of personal accountability in purely behavioural terms of
social conditioning, the problem of free-will remains a shibboleth for the
effectiveness of the scientific description. While many scientifically-trained
people consider that they may in principle be a chemical machine driven by
their brain states, the notion that subjective consciousness decision-making
has no capacity whatever to influence the physical circumstances around leads
to catatonic stasis. Everyone who
gets up in the morning and does something so predictable as pouring a cup of
coffee is making a direct investment in the notion that they are in some sense
in control of their personal decisions and that their feeling of subjective autonomy
is a valid expression of their condition.
We act in the world on this assumption and upon this investment.
Like
subjective consciousness, free-will has become an orphan of the scientific
description, seemingly inconsistent with the hypothesis that the behavior of
the organism is purely a function of its brain reacting as an electrochemical
machine, albeit a very complex one to the physical conditions of the organismÕs
environment. However, from the
outset of the quantum era, scientific researchers have noted that, since the
quantum description of reality is not deterministic, the apparently stochastic
nature of quantum uncertainty could provide a loophole for free-will, since the
universe is no longer in-principle a Laplacian mechanism [44]. Arthur Eddington [45],
for example noted that the uncertainty of position of a synaptic vesicle was
large enough to correspond to the thickness of the cell membrane, giving a
possible basis for a change in neurodynamics arising from quantum uncertainty.
Concluding that intentional volition might then be inconsistent with the chance
probability-based calculations of particle statistic, Eddington then
effectively suggested a form of hidden correlation in sub-quantum dynamics: a
correlated behaviour of the individual particles of matter, which he assumed to
occur for matter in liaison with mind.
This
ÔloopholeÕ has led to a continuing tradition of physicists, mathematicians and
brain researchers, speculating on various models by which the quantum world
might interpenetrate with the sort of brain dynamics associated with conscious
decision-making. We will look at
these in detail, once we have examined the brain dynamics associated with
conscious states.
It
has also been found that human decision-making follows rules similar to quantum
logic involving interference and states represented by vectors in Hilbert
space, which are also shared by efficient semantically-based search algorithms [46].
2 A Dynamic View of the
Conscious Brain
Unlike
the digital computer which is a serial digital device based on a discrete logic
of 0s and 1s, the brain is a massively parallel dynamic organ. Although the
action potential of long neuronal axons is a pulse coded firing rate
proportional to membrane depolarization, many neurons and indeed those forming
the organizing centre of many processes have continuously graded
potentials. Thus although some
individual neuron outputs may be pulsed action potentials, the electrical
activity of the human brain, as expressed in the eeg consists of broad spectrum
excitations indicative of chaos [47], rather than the
discrete resonances of ordered states. While some aspects of the eeg, such as
the alpha rhythms of visual relaxation, may be housekeeping activities, as
noted, oscillations in the gamma band have been associated with specific
conscious thought processes. The basis of the eeg appears to lie in dynamic
feedback between excitatory and coupled inhibitory neurons which set up mutual
oscillations through a phase-delayed feedback loop, which implicates it as a
major dynamical feature of cerebral processing.
Fig 2: Evidence for both dynamical chaos and
phase wave-front ÔholographicÕ processing. (a) Wavelet (morlet) transform,
showing time evolution of amplitudes with a peak in the gamma band accompanying
recognition of an anomalous note is consistent with phase-front processing.
Broad-spectrum excitation (extended vertical distribution of frequencies) is
also consistent with chaotic dynamics in the time domain. (b) Coherent
distribution of electroencephalogram over the cortex, is consistent with
globally coupled excitation. (c) Extended spatial distribution of cortical
activation accompanying recognition of an odour. (d) FreemanÕs [48]
[49]
model of olfactory recognition involves a transition from high-energy chaos on
inhalation to enter a new or
existing strange attractor basin as the energy is lowered on exhalation.
Although this is a transition from chaos to an ordered outcome, the attractor
may be a strange attractor, still supporting chaos locally within the basin.
(e) Fourier transforms of electroencephalogram, showing broad-spectrum
excitation and correlations dimensions consistent with global chaotic dynamics.
(f) Putative strange attractors in the electroencephalogram.
While
it might seem a contradiction that a brain state leading to any form of
strategic decision could be chaotic, this is not actually the case. Ordered dynamical systems are
inexorably drawn towards existing equilibria or resonant attractors making them
insensitive to their surroundings. A key characteristic of chaotic dynamics is
the Ôbutterfly effectÕ – their arbitrary sensitivity on their initial, or
boundary conditions – which in the words of Lorenz [50]
enable fluctuations as small as those of a butterflyÕs wings to become
amplified onto a tropical cyclone.
The
dynamical brain needs to be arbitrarily sensitive to its external conditions to
respond effectively to the sometimes very subtle clues from the world around us
that are absolutely essential for survival. A second key characteristic
particularly of high-energy chaos is that it tends to explore the entire space
of available states, sometimes called the Ôphase spaceÕ, pseudo-randomly, so
that it can appear anywhere, without prejudicing the outcome or missing an
angle. Thus a fundamental theme, which has proved very useful in exploring
brain dynamics, is a transition from chaos to order, in which an unstable
high-energy chaotic exploration falls into an ordered attracting state,
corresponding to recognition of a smell, or the ÔahaÕ of eureka that replaces the confusion of a problem with the flash of inspiration of an insight that appears to pop out of nowhere. Notably certain forms of chaotic process
consistent with analog neural nets have been claimed to work beyond the Turing
limit
[139]
.
While
these excitations may be chaotic in the time domain, the dynamics accompanying
perceptual recognition shows spatially correlated excitations similar to a
hologram, in which the recognition process arises from populations of neurons
firing together in a resonant phase-coherent manner, which distinguishes the
recognized stimulus from the random ground swell of unrelated excitations. In
this respect Karl Pribram [51],
[52]
has noted that such processes are analogous, if not identical to, quantum
measurement based on constructive phase-dependent wave interference.
Phase
coherence is consistent with chaotic dynamics in the time domain because
mode-locked resonances between oscillators are a feature of non-linear systems.
For example the heart beat, although approximately periodic, has dynamics
comparable to a chaotic sinusoidally kicked rotator [53],
which enables it to maintain mode-locked non-linear resonance with heart
pacemaker cells which in turn are under central nervous system influence.
Fig 3:
Structual outlines of the brain as a dynamical organ. (a) Major anatomical
features including the cerebral cortex, its underlying driving centres in the
thalamus, and surrounding limbic regions involving emotion and memory,
including the cingulate cortex, hippocampus and amygdala. (b) Conscious activity of the cortex is maintained
through the activity of ascending pathways from the thalamus and brain stem,
including the reticular activating system and serotonin and nor-adrenaline
pathways involved in light and dreaming sleep. (c) Processing in the cortex
consists of up to six layers of neurons, forming modular processing columns
around 1 mm in size, illustrated in cortex stained for ocular dominance
(right). (d) Such modularity is dynamic as shown by changes on ocular dominance
as a result of covering one eye during development. (e) Modular cortical
processing illustrated in pet scans of cortical activity during language
processing and the parallel processing of movement and colour in the visual
cortex.
By
contrast with a digital computer which relies on gigahertz speed to perform
discrete serial computations, the brain is a massively parallel organ, using
wave-front processing, containing between 1010 and 1011
neurons each of which can have up to 104 excitatory and inhibitory
synapses using a variety of chemical neurotransmitters to modulate
electrochemical transfer. The extreme parallel-distributed basis of this
processing is emphasized by the fact that there may only be around 10 serial
synaptic junctions between sensory input and motor output. By contrast, a
digital computer needs to make as many serial iterations as the computation
requires before coming up with an answer, and the latest PCs allow for only up
to 4 parallel units and even the largest super-computers have no more than a
few thousand, principally used in a restricted form of matrix calculation, such
as weather prediction, where each unit is essentially carrying out a similar
computation on differing initial conditions.
As
shown in figure 3, the cerebral cortex of the mammalian (and thus human) brain
consists of a large convoluted sheet about 1 m2 consisting of up to
six layers of neurons, organized into functional columns on a scale of around 1
mm2 and mini-columns of 28–40 µm performing unique processing
in a modular manner on aspects of sensory and cognitive processing, from lines
of a given orientation, through sounds of a given pitch to more abstract
features, such as recognition of specific faces, or facial expressions, to
associating the sound of a word with its semantic meaning. The cortex is
broadly divided between frontal areas responsible for action and its abstraction
in terms of plans and goals and perception and its abstractions in terms of
spatial orientation (parietal), semantic meaning (temporal) and other creative,
expressive, and classificatory skills.
The
organization of these modular columns is dynamic to the extent that covering
one eye will dynamically alter the balance of binocular dominance, and in a
blind person even use visual areas for spatial orientation based on sound
rather than vision. Many aspects of sensory processing occur in a parallel
modular manner, for example, separate local regions process colour and
movement, so that pathological conditions can result in loss of colour, or
motion perception, independently of the other.
The
electrical activity of the cortex is driven by centres in the underlying nuclei
in the thalamus, which have
reciprocal connections with corresponding areas of the cortex. In isolation, cortical tissues tend to
be electrochemically quiescent, which emphasizes that to a certain extent the
cortex represents complex boundary conditions, modulating underlying thalamic
excitations. Moreover the entire span of cortical activity accompanying waking
consciousness is dependent on a general level of excitatory activity welling up
from the brain stem centres of the reticular activating system and major modes
of dynamical brain activity modulation, such as light and dreaming sleep are
likewise modulated through ascending nor-epinephrine, dopamine and serotonin
pathways passing from the brain stem upwards to permeate specific layers of the
whole cortex.
Active
cognition is believed to involve an interplay of so-called Ôworking memoryÕ in
which frontal regions modulating the goals and direction of the thought
process, are interacting with parietal and temporal areas providing the spatial
and semantic information involved. There are actually two cortices, left and
right, connected by large parallel tracts of nerve fibres, the corpus callosum. The left and right
cortices are lateralized to varying degrees, particularly in men, so that language
articulacy and other more structured forms of cognitive processing are
predominantly in the left cortex and more generalized diffuse types of
processing occurs in the right cortex.
Consistent
with edge of chaos processing involving a transition to order from chaos,
studies of the kind of insight process that leads to phenomena such as
ArchimedesÕ ÒEureka!Ó [54] appear to
stem from the right anterior superior
temporal gyrus, when distracting structured ÔthinkingÕ activities of the
left hemisphere have been replaced by the relatively ÔcontemplativeÕ relaxation
of alpha activity.
In
addition, feedback systems involving emotional recognition, flight and fight
reactions and the establishment of long-term sequential memory surround the
periphery of the cortex in the so-called limbic system, comprising the cingulate cortex, fornix, hippocampus, amygdala and associated structures. The
semantic significance of the temporal cortex appears also to be able to combine
with the intense emotional significance of the closely associated amygdala to create mystical and other
symphonic experiences in temporal lobe epilepsy, a region coined by
Ramachandran [55],
[56]
as Òthe God SpotÓ for this mix of emotional significance and ultimate meaning.
This association may have a genetic basis in religiosity [57]
as an evolutionary adaptation enabling larger, more dominant societies [58].
Fig
4: Quantum fractality differs from classical fractality in that it becomes
discrete at the quantum level. Fractal scale transformations emerge from quantum
non-linearities forming the chemical bond, in emergent stages through tertiary
and quaternary molecular structures, to cellular organelles, cells, tissues and
finally the whole organism, with its successive bifurcations of development to
form the tissue layers and later, interactive migrations of specific cell
types. Nervous system organization is thus fractal, running from the molecular
level of ion-channels, to neurotransmitter vesicles and synaptic junctions
(upper), then to neurons (lower right), then to neuronal complexes such as
mini-columns (lower left) and finally to whole brain activation.
3 Edge of Chaos, Self-organized
Criticality and Fractal Sensitivity
Between
the global level, the cellular level and the molecular level are a fractal
cascade of central nervous processes, which in combination, make it
theoretically possible for a quantum fluctuation to become amplified into a
change of global brain state. The
neuron is itself a fractal with multiply branching dendrites and axonal
terminals, which are essential to provide the many-to-many synaptic connections
between neurons, which make adaptation possible. Furthermore, like all tissues,
biological organization is achieved through non-linear interactions which begin
at the molecular level and pass upward in a series of scale transformations
through supra-molecular complexes such as ion channels and the membrane,
through organelles such as synaptic junctions, to neurons and then to neuronal
comp-lexes such as cortical mini-columns and finally to global processes.
At
the molecular level, the ion channel is activated by one, or two,
neurotransmitter molecules. Because neurons tend to tune to their threshold
with a sigmoidal activation function, which has maximum slope at threshold,
they are capable of becoming critically poised at their activation
threshold. It is thus possible in
principle for a single ion channel, suitably situation on the receptor neuron,
e.g. at the cell body where an activation potential begins to act as the
trigger for activation.
The
lessons of the butterfly catastrophe combined with evidence for transitions
from chaos in perceptual recognition therefore suggest that if a brain state is
in a transition at the edge of chaos or is in a state of self organized
criticality, in which the system tunes to a critical state such as a sand pile
where there are fractal ÔavalanchesÕ of activity global instabilities, which
are encoding for the unresolved perceptual or conceptual context may be
ÔresolvedÕ through amplification of a local fluctuation at the neuronal,
synaptic or ion-channel level.
Fig
5: Evidence for complex system coupling between the molecular and global
levels. Stochastic activation of single ion channels in hippocampal cells (a)
leads to activation of the cells (c). Activation of such individual cells can
in turn lead to formation of global excitations as a result of stochastic
resonance (d). Individuals cells are also capable of issuing action potentials
in synchronization with peaks in the eeg (e).
Although
neuroscientists have tended to discount the idea that micro-instabilities could
lead to global changes in brain dynamics, on the basis that mass action will
overwhelm such small effects, a variety of lines of evidence have demonstrated
that fluctuations in single cells can lead to a change of brain state.
In
addition to the issue of sensitive dependence in chaotic systems, two further
lines of evidence suggest changes in ion channels and/or single cells can
influence global brain states.
The first of these phenomena is
stochastic resonance [59], in which
the occurrence of noise, somewhat paradoxically, leads to the capacity of ion
channels to sensitively excite hippocampal cells and in turn to cause a change
in global brain state. In this sense noise is playing a similar role to the
ergodic properties of dynamical chaos, which likewise distribute the dynamic
pseudo-randomly and so prevent the dynamic getting stuck into the rut of a
given ordered attractor and it is thus able to fully explore its ÔphaseÕ or
dynamical space. Thermodynamic ÔannealingÕ is likewise used in classical
artificial neural nets to avoid them becoming locked in sub-optimal local
minima.
Fig 6:
Left: Single pre-synaptic pyramidal action potential leads to multiple
post-synaptic excitations.
Right:
Structure of chandelier or axon-axonal cells with dendrites (blue) and axons
(red).
More recently it has been
discovered that a specific class of cortical neuron, the chandelier cell is
capable of changing the patterns of excitation between the pyramidal neurons
that drive active output to other cortical regions and to the peripheral
nervous system, in such a way that single action
potentials of human neurons are sufficient to recruit Hebbian-like neuronal
assemblies that are proposed to participate in cognitive processes. Chandelier
cells, which were only discovered in the 1970s, and are more common in humans
than other mammals such as the mouse, and were originally thought to be purely
inhibitory, are axon-axonal cells, which can result in specific poly-synaptic
activation of pyramidal cells [60],
[61].
The
research paper and review note:
The
increased signal-to-noise ratio in the network provided by hyperpolarizing
GABAergic synapses is further amplified by the coincident action of chandelier
cells, resulting in a sparse and potentially task-selective activation of
pyramidal neurons. Thus, the human microcircuit appears to be tuned for
unitary-EPSP–activated Hebbian-like functional cell assemblies that were
proposed as building blocks of higher-order cortical operations and could
contribute to single cortical cell–initiated movements and behavioral
responses.
This
reveals an extremely efficacious means of activity propagation in the cortical
network. Although earlier work had shown polysynaptic activations following a
single chandelier spike, the current study demonstrates much longer responses.
Moreover, one of the most interesting results relates to the temporal structure
of the activity patterns elicited after stimulation of a single neuron. While
most of them appear to propagate through the circuit with increasing
disorganization, occasionally the authors were able to trigger an amazingly
precise temporal pattern. This implies that the microcircuit is capable under
some circumstances of generating patterns of activation with low jitter and
high temporal precision.
Given
the potential for fluctuations at the molecular, ion-channel, synaptic or
neuronal level to become the organizing centre resolving instabilities in
global brain dynamic, it becomes possible to form an edge-of-chaos model for
resolving situations of cognition involving intuition, insight and the ÔeurekaÕ
attributed to ArchimedesÕ sudden discovery of his principle. In this model, the
dynamic of the ÔproblemÕ remains unresolved and thus contains instabilities,
which in turn become sensitive to perturbation on descending fractal scales
leading to the molecular and quantum level.
Such
an unstable dynamic is tending to a transition from higher-energy chaos to
order by developing a new attractor, out of the fractal diversity of repelling
attractors in the chaotic dynamic. In terms of an active brain state, this
would be likely to correspond to a global excitation, say in the gamma range
containing several uncorrelated phase components representing features of the
problem that cannot be put into coherent relationship. Hence the essential
instability at the fractal level would consist of a transition from multiple
uncorrelated phases to the emergence of a correlated Ôorganizing centerÕ
resolving the global instability.
Fig 7:
(a) EEG sweeps are coherent when anticipating a regular tone but decoherent
when the tone becomes erratic in its timing 50. (bi) Neural
connection hubs are scale independent in terms of frequency forming a small
world network consistent with self-organized criticality, (bii) Hubs compared
in resting and tapping. (c),(d) Intelligence measures correlate positively with
phase shift duration and negatively with phase lock duration 51. (e)
Evidence for self organized criticality. Sorted correlation matrix and
dendrogram of avalanches in a cortical slice 53.
A
recent growth area of research consistent with, but not limited to the edge of
chaos concept, is the development of models based on self-organized
criticality, the tuning of processes from sand piles to earthquakes towards a
critical state in which fractal avalanches maintain the process in a critical
state. In the case of a sand pile, as in an hour-glass, if the angle is too
steep, massive avalanches return it to the critical angle. Likewise, if it is
too shallow more sand will pile up with few or on avalanches until the critical
angle is reached. Edge of chaos processes share this tuning towards the
critical state at the boundary, but the reasoning also extends to stochastic systems
such as the Ising model [62] of
magnetization.
Karl
PribramÕs concept of the holographic brain [63]
has drawn attention to the deep analogy, and possible physical correspondence,
between phase coherence in brain dynamics and the wave phase basis of all quantum
measurements. Phase coherence
provides a basis for distinguishing the processes the brain is paying attention
to from the decoherent groundswell of background noise. Key experimental investigations [64],
[65]
have repeatedly confirmed a relationship between phase coherence in central
nervous electrodynamics and recognized, or anticipated, stimuli.
More
recently a variety of key experimental research results [66]
have shown a close correspondence between self-organized criticality and brain
dynamics in processing real perceptual and cognitive tasks. These are reflected in several
different forms of analysis. Study of avalanches is isolated neuronal circuits [67],
[68]
shows the avalanches are tuned to a critical threshold where a given avalanche
is like to elicit only one further one, consistent with self-organized
criticality in neural circuits.
The
fractal power law dynamics of active brains states has been found to correspond
closely with self-organized criticality related to computational simulations of
the Ising model [69]. Brain processing states have also been
found to reflect a small-world network architecture consistent with
self-organized criticality [70],
[71]
across all frequency scales used in electroencephalogram studies d,
q, a, b, g. Small-world
networks lie between regular networks, where each node is connected to its
nearest neighbours, and random networks, with no regular structure but many
long-distance connections between nodes at opposite sides of the network. A small-world
network enables communication between any two locations of the network through
just a few nodes - the "six degrees of separation" reputed to link
any two people in the world. In the brain, the number is closer to 13.
In an
intriguing 2008 study [72], high
intelligence, as measured on IQ scores, was found to consistently correlate
with longer times of phase decoherence, between phase-locked coherent states,
and shorter phase-locked episodes. The idea behind this is that longer
decoherence times corresponds to bringing larger systems of neurocircuits into
play, in cognitively analyzing a given situation and that shorter phase-locked
episodes corresponds to not getting stuck in a non-adaptive so called Ôfixed
positionÕ.
By
contrast with the earlier work on chaos in brain dynamics which tended to deal
predominantly with house-keeping states, rather than active cognition, these
studies involve intelligence and thought processes. They are consistent both
with a stochastic approach to criticality and with edge of chaos dynamics in
the active brain.
.
4 Sensory Transduction and Subjective Experience
The occurrence of
putative sensory transduction genes in the central nervous system is consistent
with a novel biophysical model supporting subjective consciousness (King [73])
- that the distributed functioning of the central nervous system provides an
'internal sensory system' which can generate abstracted sensory experiences of
reality forming an 'internal model of reality' using the same physical
principles as are involved in sensory transduction in a bi-directional manner,
enabling coherent generation and reception of biophysical excitations,
particularly those associated with vision and audition. Olfaction has a
fundamentally different basis, both in brain architecture and in the fact that
it involves specific molecular receptors, which cannot regenerate their stimuli
by reverse transduction, although there is evidence for olfactory synesthesia.
Some forms of synesthesia, such as responding with feeling to seeing another
person's finger touched, may also involve specific interactive circuitry,
including mirror neurons.
Recent research in
whole genome mapping of the mouse brain has made it possible to investigate the
potential central nervous function of genes that might otherwise be associated
primarily with peripheral sensory transduction. At the same time, the actual
molecules involved in sense transduction, in vision, hearing and touch are
being characterized. The first putative transduction molecule for mammalian
touch, stomatin-like protein 3 (SLP3, or Stoml3) was reported this year in
Nature, and putative molecules in the auditory transduction pathway, epsin, and
cadherin 23 (otocadherin) have only been reported in the last five years and
otoferlin in 2006. Research into the genetic evolution of the visual system has
also unearthed provocative new findings about vision, which became the trigger
for this hypothesis. In parallel with the usual cilia-based photo-transducer
molecule c-opsin are retinal ganglion cells, which use melanopsin, or r-opsin
related to insect opsins (based on organelles called rhabdomeres), which
depolarize rather than hyperpolarize. It has also been discovered that both
types of opsin work in opposition in the reptile parietal (pineal) eye.
At an even more basic
level, excitable neurons have ion channels which undergo conformation changes
associated with voltage, and orbital or ÔligandÕ-binding, both of internal
effectors such as G-proteins and externally via neurotransmitters, such as acetyl-choline.
They also have osmotic and mechano-receptive activation, as in hearing and can
be also activated by photoreception in certain species. At a ground level all conformation
changes of ions channels are capable of exchanging photons, phonons and orbital
perturbations representing a form of quantum synesthesia.
Fig
7b: Large scale mouse brain expression profiles of encephalopsin (Opn3),
otocadherin (Cdh23), espin (Espnl), otoferlin (Otof) and Stom3 (Allen Brain
Atlas [74])
illustrate the wide and discretely specific expression of sensory transduction
molecules for three senses, vision, hearing and touch in the central nervous
system. Does this mean that the 'internal model of reality' evokes subjective
experience using similar molecules to the physical senses?
Attention has more
recently been focused on biophotons as a possible basis of processing in the
visual cortex based on quantum releases in mitochondrial redox reactions [75],
[76],
[77].
Microtubules have also been implicated.
5 Computational Intractability, Classical Chaos and
Quantum Uncertainty
The
apparent contradiction between the idea of precise classical computation (which
abhors disrupting noise) and the apparent unruliness of chaotic excitation,
(which, although being in principle deterministic, becomes unpredictable,
through amplification of small discrepancies due to sensitive dependence,
resulting in an ÔergodicÕ trajectory, filling phase space in a similar to a
random walk) can be resolved immediately we look more closely at the sort of
computational problems a living nervous system actually needs to solve in
minimal time to survive.
The
traveling salesman problem – how to find the shortest path around n cities – is classed as np-complete [78].
Characteristically to classically compute a given solution requires checking
each of the possible cyclic
paths and finding the smallest.
However because this is super-exponential, even for a small number of
cities like say 25, the computation time required stretches out to the age of
the universe. The same
consideration applies to virtually every environmental decision-making process
a living organism faces, such as which path to take to the water hole, since
these all involve an exponentially increasing number of combinations of contingent
factors in the open environment. An animal cannot afford to wait more than a
split second making a real survival decision, or it may be leapt upon by a
tiger and consumed, so nervous systems have to find an immediate real-time way
of solving any such potentially intractable decision-making problem.
The
solution used by artificial neural nets, which model a problem like the
traveling salesman problem as an energy minimization on a landscape
representing the distances between the cities, is to apply thermodynamic
annealing, starting with a high temperature which prevents the dynamic becoming
stuck in a high local minimum, gradually reducing the temperature of random
fluctuations, arriving at a reasonable sub-optimal local minimum. Statistical
computational methods of solution work similarly.
The
Freeman model of perception fig 2(d) uses a transition from high-energy chaos
to a lower energy strange-attractor in much the same way, using the high-energy
chaos to avoid the system becoming trapped in a far-from-optimality attractor
until the ÔphaseÕ space of the system has been fully explored.
Such a
system provides for a smooth transition between a situation in which the
boundary conditions lead to a clear computational outcome and hence a decision
based on one choice having a manifestly higher probability of survival, and
other situations, in which, like the problem of ArchimedesÕ possibly crown,
there is no predisposing resolution of the system because the problem has not
yet been solved and the contextual factors remain ambiguous, or inconsistent.
Unlike
the discrete Von Neumann or Turing machine, biological nervous systems appear
to work on dynamical principles which provide the capacity to induce a
transition from chaos to order, where the classical computer would run into the
Turing halting problem – unable to determine whether, or when, the
computational process will end.
Clearly
such a transition will involve sensitive dependence on initial and other
boundary conditions and will be in a classical sense unpredictable (just as the
butterfly effect is) and since it involves molecular processes at the quantum
level, may invoke quantum uncertainty as well. We thus need to investigate how
these two effects might come together, and explore whether and how they might
play upon the processes of perceptual recognition and conceptual insight.
The
first point of reference is a brief review of the wave-particle relationship
and how the uncertainty relationship comes about. By EinsteinÕs law , the energy of a particle is equivalent to the frequency of
the wave as the momentum is likewise to the wavelength. If we then want to
measure the energy, this will be equivalent to measuring the frequency, but as
we canÕt sample parts of a quantum wave, the only way we can know the frequency
is effectively to count the beats against a reference frequency. The time delay
between
successive fronts where the two waves are in phase, giving constructive
interference, then gives us the uncertainty relation
.
Constructive
interference from corresponding phase fronts passing through two slits also
gives us the basis in wave-particle complementarity of the two-slit
interference experiment fig 8.
Complementarity is demonstrated in the release of a photon from an
excited atom in the bulb, as a discrete localized ÔparticleÕ, corresponding to
an orbital transition from an excited atomic orbit. The photon then travels
through both slits as a wave, which overlaps itself to form bright bands of
constructive interference and is again absorbed as a particle by a silver atom
on the photographic film. Although
these discrete particles arrive one at a time and could appear anywhere the
wave function is not precisely zero, as numbers of particles arrive, their
statistical probability of occurrence is distributed according to the complex
square of the amplitude of the wave .
Fig 8: Top right: Beats
of constructive wave interference determine the uncertainty principle. Bottom:
Two-slit interference experiment illustrates wave-particle complementarity. Top
left: Cat Paradox experiment.
The
particle incidence gives rise to one of the fundamental unresolved questions of
quantum theory. As the wave function doesnÕt determine where the particle
should end up, it is deemed that the wave function has ÔcollapsedÕ at the point
the particle is detected and unlike the linear evolution of the wave function,
this collapse process is stochastically unpredictable, leading to the idea that
there may be a deeper Ôhidden variableÕ theory explaining how each photon
actually ÔdecidesÕ where it ends up.
The
contrast between quantum theory, which leads only to parallel probabilities
that the photon could be anywhere in its wave function, and the real world in
which unique histories always occur, led to Schršdinger coining the Ôcat
paradoxÕ, in which a cat is predicted to be both alive and dead by quantum
theory with differing probabilities, if a Geiger counter is set to break a vial
of cyanide, but when we open the box the cat is either alive, or dead but not
both. Various approaches, including hidden variable theories and quantum
decoherence [79]
caused by interaction with Ôthird-partyÕ quanta have been invoked to explain
this process but none eliminate the essential complementarity.
When
we come to consider how systems, which would classically display features of
chaos behave in the quantum world, we find a series of apparent contradictions,
in the so-called quantum suppression of chaos. In fig 9 the quantum stadium is
used to illustrate several features of this phenomenon. The classical stadium billiard is
chaotic because the periodic orbits, some of which are shown in (d), are
unstable, so that a ball with a trajectory differing by an arbitrarily small
amount is deflected by increasing amounts by the curved boundary of the region,
so that the periodic orbits are all repelling and almost every orbit is a
chaotic trajectory which eventually fills the region ÔergodicallyÕ in an
unpredictable, pseudo-random manner, as in (a), due to sensitive dependence on
initial conditions.
The
quantum wave function solutions (b) work differently, displaying peaks of the
probability function around the periodic orbits, defying their repelling
nature. The reasons can be easily
understood of we use a semi-classical approximation, by releasing a small wave
packet and watching the way it bounces back and forth as in (c). Whenever the
wavelength of the packet forms a rational relationship with the length around a
transit any of the reflecting periodic orbits, we get an eigenfunction of the
quantum wave function, which constructively interferes with itself, as a
standing wave, just as do the orbitals of an atom, to form a probability peak
around the periodic orbit. Even when a trajectory is a little off the periodic
orbit, the spreading wave packet still overlaps itself contributing to the
probability peak.
The
end result is that for a variety of closed quantum systems, wave spreading eventually
represses classical chaos by scarring, causing the periodic eigenfunctions to
become eventual solutions of any time-dependent problem, although the initial
trajectory behaves erratically, just as does an orbit in the classical
situation. For example, a periodically kicked quantum rotator [80],
[81]
will stochastically gain energy, just as in the classical situation, until a
quantum break time [82], after
which it will become trapped in one of the quantum solutions. A highly excited atom in a magnetic
field will have its absorbance peaks at the periodic solutions, and quantum
tunneling will likewise use scarred eigenvalues as its principle modes of
tunneling [83],
[84].
Fig 9:
Quantum chaos: The classical stadium billiards is chaotic. A given trajectory has sensitive
dependence on initial conditions. As well as space-filling chaotic orbits (a) [85],
the stadium is densely filled with repelling periodic orbits, three of which
are shown in black in (d). Because they are repelling, neighbouring orbits are
thrown further away, rather than being attracted into a stable periodic orbit,
so arbitrary small deviations lead to a chaotic orbit, causing almost all
orbits to be chaotic. The quantum solution of the stadium potential well (b) [86]
and (d) [87]
shows ÔscarringÕ of the wave function along these repelling orbits, thus
repressing the classical chaos, through probabilities clumping on the repelling
orbits. A semi-classical simulation (c) shows why this is so. A small wavelet bounces back and forth,
forming a periodic wave pattern, because even when slightly off the repelling
orbit the wave still overlaps itself and can form standing wave constructive
interference when its energy and frequency corresponds to one of the
eigenvalues of a periodic orbit, even though the orbit is classically
repelling. The quantum solution is
scarred on precisely these orbits (d).
This causes resonances such as absorption peaks of a highly magnetically
excited atom (e) to coincide with the eigenfunctions of the repelling periodic
orbits, just as the orbital waves of an atom constructively interfere with
themselves, in completing an orbit to form a standing wave, like that of a
plucked string. The result is that, over time, in the quantum system, although
the behaviour may be transiently chaotic, it eventually settles into a periodic
solution. Experimental realizations such as the scanning tunneling view of an
electron on a copper sheet bounded by a stadium of carefully-placed iron atoms
(f) [88],
confirm the general picture, although, in this experiment, tunneling leaked the
wave function outside too much to demonstrate proper scarring. The
semi-classical approach matches closely to the full quantum calculation (g).
These
constraints do not apply to open systems, such as molecular kinetics where
diffusion can carry molecules relatively vast distances. As a rough example, a glycine molecule
at biological temperatures has a self-diffraction angle of wave-spreading of
about 6.5o, showing this effect is significant [89].
Moreover, the larger the system, the longer the delay until quantum break time
sets in.
The
implication is that sensitive dependence on initial conditions eventually gives
way, at the quantum level, to quantum uncertainty of the scarred orbit,
globally traversing the space concerned, and it does so by performing a
transition from chaos to order dependent on the initial conditions initially
following a chaotic trajectory and eventually entering into a periodic
orbit. Since a chaotic system,
whether quantum or classical has a dense set of periodic orbits there, is
potentially an infinite number of these, although quantum separation of chaotic
eigenfunctions [90], another
feature of quantum repression of chaos, will lead to only a finite number being
available at the energies concerned.
The
implications are threefold:
1. Quantum
suppression of chaos leads to a situation where:
(a)
quantum chaotic systems model a transition from chaos to order, just as insight
processes involve a transition from chaos to order, and
(b)
quantum suppression of chaos by phase coherence parallels the way brain
processes may use coherence to distinguish critical processes in conscious
attention from the background.
2. The
eigenfunctions of chaotic quantum processes are globally distributed over the
phase space and thus, in so far as the outcomes depend on stochastic properties
of wave-particle reduction, enable uncertainty to affect outcomes on the scale
of the phase space orbit.
3. In processes that
involve open systems, or large phase spaces whose quantum break time is much
longer than the real time window, chaos and quantum uncertainty may combine to
amplify uncertainty, so that it can affect global outcomes.
An
indication of how the transition from classical to quantum chaos might lead to
complex forms of quantum entanglement can be gleaned from an ingenious
experiment forming a quantum analogue of the kicked top using an ultra-cold
cesium atom kicked by both a laser pulse and a magnetic field. In figure 9b is shown the classical
dynamical phase space of the kicked top showing domains of order where there is
periodic motion and complementary regions of chaos where there is sensitive
dependence on initial conditions as a result of horseshoe stretching and
folding. In the quantum system (second row) in the ordered region (left), the
linear entropy of the system is reduced and there is no quantum entanglement
between the orbital and nuclear spin of the atom. However in the chaotic region
(right) there is no such dip, as the orbital and nuclear spins have become
entangled as a result of the chaotic perturbations of the quantum topÕs motion [91],
[92].
Fig 9b
Classical and quantum kicked top and entropies.
6 The Evolution of Chaotic Sensitivity and the Emergence
of Consciousness
We now
return to the biological arena, to consider how nervous systems might have
evolved the dynamics we associate with consciousness. Is the sort of dynamics we associate with the conscious
brain a product of the complex interconnectivity of circuitry of relatively
trivial neurons, as work with artificial neural nets and computational
approaches, such as artificial intelligence might suggest? Or is it a
fundamental aspect of living cells, which evolved with the earliest eukaryotes?
Is it in the senses of a single celled-organism that we will naturally find the
origin of chaotic excitability as a source for the quantum sensitivity that
ultimately shaped the evolution of the conscious brain in higher organisms?
A
realistic assessment of pyramidal neurons confirms that they are very complex
dynamical systems in their own right, far from the trivial additive units which
McCulloch-Pitts ÔneuronsÕ present in theoretical artificial networks,
containing up to 104 synaptic junctions, having a variety of
excitatory and inhibitory synaptic inputs involving up to four or five
different types of neurotransmitter, with differing effects depending on their
location on dendrites, the cell body, or axon-axonal connections.
Furthermore
many of the critical features we associate with neurons, and their associated
neuroglia, in the conscious brain, including excitability and the use of
neurotransmitter molecules, are not only shared by other cells in the human
body, but extend down to the earliest single-celled eukaryotes [93].
Choanoflaggelates which lie at the base of multcellular evolution contain
several pathways essential for brain function, including sodium and calcium ion
channels and signalling proteins [94]
The
connection between bursting and beating in excitable cells was established by
the Chay-Rinzel model and ensuing experiments [95],
which established chaotic dynamics in neurons, pancreatic b-cell
exocytosis, and inter-nodal cells in the alga Nitella [96]. The
association between excitability and exocytosis spanning the eukaryotes [97]
is doubly significant in that, in addition to graded electrochemical and action
potentials in the neuron, synaptic vesicles are also produced by exocytosis.
Earlier
work had already demonstrated membrane potentials in Amoeba proteus [98] associated
with pseudopod formation, and action potentials in the amoeba Chaos chaos [99],
[100],
aptly so-named by Linnaeus [101]. In
ciliated protozoa, such as Paramecium,[102],
[103]
and Tetrahymena [104]
action potentials are associated with the motile actions of cilia in cellular
locomotion.
The
aggregation of slime moulds such as Dictyostellium
is mediated by cyclic-AMP [105],
[106].
The ciliated protozoan Tetrahymena
pyriformis [107],
[108]
and flagellated Crithidia
jasciculata [109]
utilize serotonin, and the former also metabolizes
dopamine and epinephrine [110],
[111].
Tetrahymena pyriformis also has circadian light-related
melatonin expression [112].
Fig 10: Real-time purposive
behavior in single cells (a) Paramecium
reverses, turns right and explores a cul-de-sac. (b) Human neutrophil chases an
escaping bacterium (black), before engulfing it. (c) Chaos chaos engulfs a paramecium.
Action potentials in Chaos chaos (d)
and paramecium (e). Period 3
perturbed excitations in Nitella
confirm chaos. (g) Frog retinal rod cells are sensitive to single quanta in an
ultra-low intensity beam, with an average rate of one photon per click, but
sometimes zero, or two, due to uncertainty in the beam.
Both
amoebae and ciliates show purposive coordinated behaviour over real time, as do
individual human cells such as macrophages. The multi-nucleate slime mould Physarum polycephalum
can solve shortest path mazes and demonstrate a memory of a rhythmic series of
stimuli, apparently using a biological clock to predict the next pulse [113],
[114].
Chaotic
excitation provides an excitable single cell with a generalized quantum sense organ.
Sensitive dependence would enable such a cell to gain feedback about its
external environment, perturbed by a variety of quantum modes - chemically
through molecular orbital interaction, electromagnetically through photon
absorption, electrochemically through the perturbations of the fluctuating fields generated by the
excitations themselves, and through acoustic and mechanical interaction. Amoebae for example, although they lack
specific sense organelles, are highly sensitive to chemical and electrical
signals, as well as to bright light.
Such excitability in the single
cell would predate the computational function of neural nets, making dynamical
chaos fundamental to the evolution of neuronal computing rather than vice
versa. A single cell has no capacity to solve decision-making problems through
a neural net consisting of many cells, so has to rely on membrane excitation
and internal regulatory systems, such as biological clocks and genetic switches
to provide memory and a strategy for survival.
Fig 11:
Hydra has only an undifferentiated nerve net (a), yet catches prey by
coordinated action of its tentacles (b) and has no less than 12 different forms
of motion, from stages of somersaulting to snail-like gliding.
When we move to the earlier
metazoa such as Hydra, we already
have many of the neurotransmitters, G-linked protein receptors, ion channels
and essentially all the neuronal machinery we associate with vertebrate nervous
systems, causing the basis of central nervous system function and dynamics to
be common to the entire animal kingdom. Hydra,
which supports only a primitive diffuse neural net and whose tissues can
dynamically reorganize themselves, for example if it is turned inside out, we
find the organism has a rich repertoire of up to 12 forms of ÔintuitiveÕ
locomotion, and is able to coordinate tentacle movements and tumbling, and
other forms of movement using similar global dynamics to those in amoebae and Paramecium, or a more advanced organism,
such as a snail. We can thus see that nervous systems have arisen from the
adaptive dynamics of individual eucaryote cells, rather than being composed of
a logical network made out of essentially trivial formal neurons.
As we move up the evolutionary
tree to complex nervous systems, such as in vertebrates, we still see the same
dynamical features, now expressed in whole system excitations such as the eeg,
in which excitatory and inhibitory neurons still provide a basis for
broad-spectrum oscillation, phase coherence and chaos in the global dynamics,
with the synaptic organization enabling the dynamics to resolve complex
context-sensitive decision-making problems, involving memories of past
situations and specific adaptations to current ones. However the immediate decision-making situations around
which life or death results, in the theatre of conscious attention in real
time, are qualitatively similar in nature to those made by single celled
organisms, such as Paramecium, based
strongly on immediate sensory input, combined with a short term anticipation of
immediate threats, in a context of remembered situations from the past that
bear upon the current existential strategy.
Looking back more deeply in
time, chaotic excitability and electrochemistry generally may be one of the
founding features of eucaryote cells, dating from the RNA era, before coded
protein translation [115],
[116],
[117].
Nucleotide coenzymes, believed to be molecular fossils from the RNA era,
pervade electron transport pathways. Key chemical modifiers may have been
precursors of the amine-based neurotransmitters, spanning acetyl-choline,
serotonin, catecholamines and amino acids such as glutamate and GABA, several
of which have potential pre-biotic or trans-biotic status. Positive amines for
example may have chemically complemented negatively charged phosphate-based
lipids in modulating membrane excitability in primitive cells without requiring
complex coded proteins.
The sense modes we experience
are not simply biological as such, but more fundamentally are the qualitative
modes of quantum interaction between molecular matter and the physical
universe. They thus have potential cosmological status. Vision deals with
interaction between photons and orbitals, hearing with the harmonic excitations
of molecules and membrane solitons, as evidenced in the action potentials
arising from cochlear cells. Smell is the consequence of orbital-orbital
interaction, as is taste. Touch is a hybrid sense involving a mixture of these.
The limits to the sensitivity of
nervous systems are likewise constrained by the physics of quanta, rather than
biological limits. This is exemplified by the capacity of
retinal rod cells to record single quanta fig 10(g), and by the fact that
membranes of cochlear cells oscillate by only about one H atom radius at the
threshold of hearing, well below the scale of individual thermodynamic fluctuations
and vastly below the bilayer membrane thickness. Moth pheromones are similarly
effective at concentrations consistent with one molecule being active, as are
the sensitivities of some olfactory mammals.
The very distinct qualitative
differences between vision, hearing, touch and smell do not appear to have a
physiological support in the very similar patterns of electrical excitation
evoked in their cortical areas. However, if all these excitations can occur
simultaneously in the single cell, chaotic excitation could effectively become
a form of cellular multi-sensory synaesthesia [118],
which is later specialized in the brain in representing each individual sense
mode. Thus in the evolution of the cortical senses from the most diffuse,
olfaction, the mammalian brain may be using an ultimate universality, returning
to the original quantum modes of physics in a way which can readily be
expressed in differential organization of the visual, auditory, and
somato-sensory cortices according to a single common theme of quantum
excitability. This is consistent with cortical plasticity, which for example,
enables a blind person
to use their visual areas for
other sensory modes.
It is thus natural to postulate
that cellular ÔconsciousnessÕ, as a focused global dynamical electrochemical
response to a cellÕs environment, is a pivotal feature which as been elaborated
and conserved by nervous systems because it has had unique survival value for
the organism. It is a logical
conclusion that the conscious brain has been selected by evolution because its
biophysical properties provide access to an additional principle of
predictivity not possessed by formal computational systems. One of the key
strategies of survival implicated in brain dynamics is anticipation and
prediction of events [119],
[120],
[121],
[122]. Computational systems achieve this by a
combination of deductive logic and heuristic calculation of contingent
probabilities. However quantum
non-locality may also provide another avenue for anticipation, which might be
effective even across the membrane of a single cell, if wave reductions are
correlated in a non-local manner in space-time. We shall examine this possibility next.
7 Quantum Entanglement and the Transactional
Interpretation
All
forms of quantum field theory stem from the special relativistic form of the
energy . This gives two
solutions, one a positive energy solution traveling in the usual (retarded)
direction in time and the other a negative energy (advanced) solution,
traveling backwards in time.
All quantum mechanical
calculations are based on these dual solutions of special relativity, including
those of quantum electrodynamics, the most accurate physical theory ever
devised [123].
Wheeler and Feynman noted that ÔabsorberÕ theory [124],
in which the advanced solutions were included, gave the same predictions as
descriptions in which the advanced solutions were omitted as unphysical. Indeed
all Feynman space-time diagrams implicitly contain both the advanced and
retarded solutions.
For a photon, which is its own
anti-particle, the advanced and retarded solutions of electron-electron
repulsion by exchanging virtual particles fig 12(3a-c) are identical, as a
negative energy advanced photon IS a positive energy retarded photon. Likewise
electron scattering becomes positron creation-annihilation when time reversed
(d). The delayed choice experiment and quantum erasure, fig 12 (1,2) confirm
that changes after emission, or even at absorption, can influence the path
taken by a photon or other exchanged particle [125].
In John CramerÕs transactional
interpretation [126], such an
advanced Ôbackward travelingÕ wave in time gives a neat explanation, not only
for the above effect, but also for the probability aspect of the quantum in
every quantum experiment. Instead of one photon traveling between the emitter
and absorber, there are two shadow waves, which superimposed make up the
complete photon. The emitter transmits an offer wave both forwards and
backwards in time, declaring its capacity to emit a photon. The potential
absorbers of this photon transmit a corresponding confirmation wave. These,
traveling backwards in time, send a hand-shaking signal back to the emitter, fig 12(4a). The offer and confirmation waves
superimpose constructively to form a real photon only on the space-
time path connecting the emitter
to the absorber.
Fig 12: Wheeler delayed choice
experiment (1) shows that a decision can be made after a photon from a distant
quasar has traversed a gravitationally lensing galaxy by deciding whether to
detect which way the photon traveled or to demonstrate it went both ways by
sampling interference. The final state at the absorber thus appears to be able
to determine past history of the photon. Quantum erasure (2) likewise enables a
distinction already made, which would prevent interference, to be undone after
the photon is released. Feynman diagrams (3) show similar time-reversible
behavior. In particular time reversed electron scattering (d) is identical to
positron creation-annihilation. (4a) In the transactional interpretation, a
single photon exchanged between emitter and absorber is formed by constructive
interference between a retarded offer wave (solid) and an advanced confirmation wave (dotted).
(b) EPR experiments of quantum entanglement involving pair-splitting are
resolved by combined offer and confirmation waves, because confirmation
waves intersect at the emission point. Contingent absorbers of an emitter in a
single passage of a photon (c). Collapse of contingent emitters and absorbers
in a transactional match-making (d).
The transactional interpretation
offers the only viable explanation for the apparently instantaneous connections
between detectors in pair-splitting EPR experiments in which a pair of
correlated photons are emitted by a single atom [127],
[128],
[129],
in which neither of the photons has a defined polarization until one of them is
measured, upon which the other immediately has complementary polarization. In fig 12(4b), rather than
a super-luminal connection between detectors A1 and A2, the two photonsÕ
advanced waves meet at the source emission point in a way which enables the
retarded waves to be instantaneously correlated at the detectors. One can also
explain the arrow of time, if the cosmic origin is a reflecting boundary that
causes all the positive energy real particles in our universe to move in the
retarded direction we all experience in the arrow of time and increasing
entropy [130].
The hand-shaking space-time
relation implied by the transactional interpretation makes it possible that the
apparent randomness of quantum events masks a vast interconnectivity at the
sub-quantum level, reflecting BohmÕs implicate order [131],
although in a different manner from BohmÕs pilot wave theory [132].
Because
transactions connect past and future in a time-symmetric way, they cannot be
reduced to predictive determinism, because the initial conditions are insufficient
to describe the transaction, which also includes quantum boundary conditions
coming from the future absorbers. However this future is also unformed in real
terms at the early point in time emission takes place. My eye didnÕt even
exist, when the quasar I look out at emitted its photon, except as a profoundly
unlikely branch of the combined probability ÔwavesÕ of all the events
generating parallel Ôprobability universesÕ throughout the history of the
universe between the time, long ago, that the quasar released its photon, and
me being in the right place, at the right time to see it distant epochs
later.
In the extension of the
transactional approach to supercausality [133],
[134],
a non-linearity collapses the set of contingent possibilities to one offer and
confirmation wave, fig 12 (4c,d). Thus at
the beginning, we have two sets of contingent emitters and absorbers and at the
end each emitter is now exchanging with a specific absorber. Before
collapse of the wave function, we have many potential emitters interacting with
many potential absorbers. After all the collapses have taken place, each
emitter is paired with an absorber. One emitter cannot connect with two
absorbers without violating the quantum rules, so there is a frustration
between the possibilities, which can only be fully resolved if emitters and
absorbers are linked in pairs. The number of contingent emitters and absorbers
are not necessarily equal, but the number of matched pairs is equal to the
number of real particles exchanged.
This transactional time symmetry
is paralleled in the implicit time reversibility of quantum computation, which
also depends on a superposition of states. Recent experiments with photosynthesis [135]
have shown how quantum computation could play an integral role in biological
and hence brain processes. When a photosynthetic active centre absorbs a
photon, the wave function of the excitation is able to peform a quantum
computation which enables the excitation to travel down the most efficient
route to reach the chemical reaction site. The
transactional interpretation may thus combine with effective forms of
biological quantum computation to produce a space-time anticipating quantum
entangled system, which may be pivotal in how the conscious brain does its
processing.
It is at this point that the influence of the
conscious observer and the hard problem become an intriguing challenge to the
scientific description. The brain is not a marvelous
computer in any classical sense - we can barely manage a seven-digit span, but
it is a phenomenally sensitive anticipator of environmental and behavioral
change. Subjective consciousness has its survival value in enabling us to jump
out of the way when a tiger is about to strike, not so much in computing which
path the tiger might be on, (because this is an intractable problem, and the
tiger can also take it into account in avoiding the places we would expect it
to most likely be), but by intuitive conscious anticipation.
Fig 13: Evidence of
immediate anticipatory subjective consciousness. A seagull just manages to escape
a shark strike, before flying off.
The
brain, using phase correlation in its own wave dynamics, as a basis for
decision-making, parallels the way in which the wave function and its
constructive interference determines the probabilities in the reduction of the
wave packet. We thus may need to consider the possibility that global brain
excitations form an ÔinflatedÕ quantum system and that the brain uses a form of
quantum anticipation involving emission and absorption of its own excitations
in a way which enables it to have an ÔintuitiveÕ non-computable representation
of future states which complement computational processing and which would be
unavailable to a classical computer. Quantum coherence is already a technique
in imaging, demonstrating an example of quantum coherence in biological tissues
at the molecular level [136],
[137].
In
this sense, the enigma of subjective consciousness may exist partly because
such excitations cannot be reduced to classical prediction, or quantum
transactions would introduce a causal Ôback-to-the-futureÕ feedback loop. Thus
the brain, in developing the internal model of reality represented by the
ÔCartesian theatreÕ, may have opted for a complementarity between subjective
consciousness and objective brain function, to maintain ÔentangledÕ
anticipation, which is an evolutionary adaptation to the transactional
relationship underlying wave-particle complementarity, bringing the two
complementarities into conjunction.
Fig 14:
Transactional view of a hunter trying to find a safe path to the waterhole.
Both the open hilly path and the jungle path (right) have lions or tigers,
which might attack the hunter. Paranoia suggests the hunter takes the hilly
path as his quantum anticipation makes him feel uneasy about the forested path,
since in the probability universe where he take this path he gets a severe
fright. Usually these anticipations will be almost immediate, as in fig 13.
In this
respect, subjective consciousness may present an existential cosmological
situation, as noted in Indian philosophy, in which consciousness is described
as ÔfinerÕ than matter, thus gaining a complementary existential status to the
physical universe, in the manner of the Tantric dance of Shiva as the undivided
field of subjective consciousness and Shakti as maya – the multiplicity of material manifestations, again
reflecting the continuous-discrete wave-particle relationship, and do this by
manifesting in subjective consciousness aspects of the space-time traversing
sub-quantum dynamics that underlies the wave-particle complementarity at the
foundation of the quantum description of the cosmological universe.
To make this point in a closing
tale we narrate the following descriptive evolutionary account.
A hunter is at a fork in the path to the water hole, seeking to
get an antelope for meat, but wary of himself getting taken by a big cat in the
process. As the man stands pondering and studying the tracks on the path and
the sounds and smells blowing across the savannah and through the jungle, his
brain develops a resonant coherent excitation – the hunterÕs ÔstealthÕ
– a state of awareness empty of structured thought, anticipating the
slightest movement around him.
There are two histories of varying duration, from immediate
awareness, to the imminent future, that the vagaries of fate on the day could
bring about. The man could walk down the shady path or the one over the rocks.
As things transpire, there is a hungry tiger on the shady path,
which is poised to leap on anything coming its way. However the manÕs brain
wave is resonating in an entanglement with his future brain states and there
are two parallel universes of future states, one down the shady path and the
other down the rocky one.
Now the brain state going down the shady path has a catastrophe -
one hell of a scare, or outright death, painfully mauled by the big cat. The
hunterÕs stalking brain state gets absorbed down there and the absorber's
advanced wave runs back through space-time in his brain state along the path he
just traversed, to the point where the man is still standing at the fork trying
to decide what to do.
On the other path he simply walks to the water hole, because the
lions are elsewhere today, and shoots a small antelope with his poisoned arrow
and takes it back to a woman in the village, so she might consent to have sex
with him. This outcome also absorbs the resonating brain wave and sends its
advanced wave back to the hunter at the crossroads, but it doesnÕt excite his
paranoia.
At the crossroads the man is feeling disquiet. His amygdala is giving him conniptions
of foreboding. He feels bad about the shade under the trees. He doesn't like the rocky path either,
because lions spend a lot of time slouching in the little gullies in the rocky
hills, but having already pondered for long enough to contemplate, and being
desirous of having sex before the moon sets, he decides, on a sheer hunch,
which he canÕt fully describe, to go ahead on the hunt, by walking carefully
along the stony path.
He ends up having children and his children have too and each have
often since felt pretty paranoid about a lot of things, but sometimes they just
feel its a sunny day, and the shade under the trees looks cool, and although a
few have been picked off by big cats, most of them have taken some good hunks
of meat back to the village and had some sex for themselves too. And so the
story carries on long enough for the hunterÕs great-grandson to sit down and
get ready to share a good roast leg of antelope, while the women throw some
sweet potatoes into the fire, to pick up his flute and cock his bowstring
against a cooking pot to pluck for a tune, and tell a few jokes, and scary
stories too, to get the woman he admires to draw in close and put her arms
around him, and do that funny thing of wiggling her middle finger in the palm
of his hand that means she wants to take him off for the night for a Ôwalking
marriageÕ, once the fire has died down low [138].
So it is that the anticipatory quantum chaos of the living cell
has become the contemplative mind of the lonely hunter, in the generations of
conscious beings traversing the sentient wave-particle universe.
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