Age-old battle lines over the puzzling nature of mental experience
are shaping a modern resurgence in the study of consciousness.
On one side are the long-dominant "physicalists" (reductionists,
materialists, functionalists, computationalists. . ) who see
consciousness as an emergent property of the brain's neural networks
("brain = mind = computer"). On the alternative, rebellious
side are those who see a necessary added ingredient: proto-conscious
experience intrinsic to reality, perhaps understandable through
modern physics (panpsychists, pan-experientialists, "funda-mentalists").
It is argued here that the physicalist premise alone is unable
to solve completely the difficult issues of consciousness (e.g.
experience, binding, pre-conscious conscious transition, non-computability
and free will) and that to do so will require supplemental panpsychist/pan-experiential
philosophy expressed in modern physics. In one such scheme proto-conscious
experience is a basic property of physical reality accessible
to a quantum process associated with brain activity. The proposed
process is Roger Penrose's objective reduction (OR), a
self-organizing "collapse" of the quantum wave function
related to instability at the most basic level of spacetime geometry.
In the Penrose-Hameroff model of "orchestrated objective
reduction" ("Orch OR"), OR quantum computation
occurs in cytoskeletal microtubules within the brain's neurons
and links cognition with proto-conscious experience and Platonic
values embedded in spacetime geometry. The basic idea is that
consciousness involves brain activities coupled to self-organizing
ripples in fundamental reality.
Introduction - A Burning Issue
Can conscious experience-feelings, qualia, our "inner life"-be
accommodated within present-day science? Those who believe it
can (e.g. physicalists, reductionists, materialists, functionalists,
computationalists) see conscious experience as an emergent property
of complex neural network computation. Others see conscious experience
either outside science (dualists), or believe science must expand
to include experience (idealists, panpsychists, pan-experientialists,
"funda-mentalists"). These philosophical battle lines
were originally drawn in ancient Greece between Socrates, who
believed the cerebrum created consciousness, and Aristotle, Democritus,
Thales and others who argued that mental qualities belonged to
fundamental reality. Perhaps both sides were correct.
Brain = Mind = Computer?
The basic physicalist idea is that the mind is a computer functioning in the brain's neural networks. The current leading candidate for a computer-like "neural correlate" of consciousness involves synchronously oscillating feedback loops of thalamo-cortical neurons. Higher frequencies (collectively known as "coherent 40 Hz") have been suggested to mediate temporal binding of conscious experience (e.g. Singer, Gray, Crick and Koch, etc.). The proposals vary, for example as to whether coherence originates in thalamus or resonates in cortical networks, but "thalamo-cortical 40 Hz" stands as a prevalent view of the substrate for consciousness.
But how do synchronized neural firings and synaptic transmissions produce experiential qualia, emotions or free will? Physicalists believe this to be relatively straightforward (brain = mind = computer) however others find the question intractable, or as vexing as trying to coax a reluctant genie from a magic lamp. I see three problems with the brain = mind = computer analogy:
1) Is consciousness classical computation? In a controversial stance Roger Penrose 1-3 has asserted that essential aspects of consciousness are non-computable. But regardless, classical computers appear to be evolving toward quantum computers. Beginning in the early 1980's Benioff, Feynman and others proposed that states in a system - bits in a computer - could interact while in quantum superposition of all possible states, effecting near-infinite parallel computation. Rather than classical Boolean bit states 1 or 0, quantum computers would utilize interactive "qubits" of 1 and 0. If quantum computers can ever be constructed they will have huge advantages in important applications. As the brain/mind has always been cast as current information technology, consciousness may inevitably be seen as some form of quantum computation.
2) Are neural firings the "fine grain" of consciousness?
Cells and synapses are far more complex than simple onoff
switches. Consider the paramecium, a single cell organism which
gracefully swims, avoids predators, learns to escape from capillary
tubes, and finds food and mates. Observing intelligent behavior
in unicellular creatures C.S. Sherrington said in 1951: "Of
nerve there is no trace. But the cell framework, the cyto-skeleton,
might serve." Lacking synapses, paramecium utilizes its cytoskeleton
for communication and organization. Neurons have a rich and dynamic
set of cytoskeletal microtubules which regulates synapses, and
tremendously increases potential computational capacity (e.g.
1016 bit states/second/neuron)4. More importantly,
neurons are alive and we don't yet know what that implies for
3) Details which don't fit the brain = mind = computer scheme are overlooked.
a) Neurotransmitter vesicle release and cognitive reaction times are "noisy", and exhibit apparent probabilistic randomness (?noncomputable quantum indeterminacy5).
b) Axonal firing patterns (rather than average frequency) and dendriticdendritic processing may be relevant to consciousness6.
c) Apart from chemical synapses, primitive electrotonic gap junctions couple neurons and glia synchronously and may play an important role in consciousness.
d) Glial cells (80% of the brain) are ignored in the brainascomputer view.
Quibbling aside, the physicalist view fails to address difficult
issues. For example the problem of 'binding' in vision
and self is often attributed to temporal correlation (e.g. coherent
40 Hz), but it is unclear why temporal correlation per se
should bind experience without an explanation of experience. Regarding
transition from preconscious or implicit processing to consciousness
itself, the physicalist view sees emergence at a critical level
of neural-level computational complexity. But no conscious threshold
is apparent, nor is there a reasonable suggestion why such an
emergent property should have conscious experience. As physicalism
is based on deterministic computation, it is also unable to account
for free will or Penrose's proposed noncomputability. But
the major problem remains experience, for which physicalism offers
no testable predictions. Something is missing.
Panpsychism Meets Modern Physics
Perhaps panpsychists are in some way correct and components of
mental processes are fundamental, like mass, spin or charge. Following
the ancient Greek panpsychists, Spinoza (1677) saw some form of
consciousness in all matter. Leibniz (1766) portrayed the universe
as an infinite number of fundamental units ("monads")
each having a primitive psychological being. Whitehead (e.g. 1929)
was a process philosopher who viewed reality as a collection of
events occurring in a basic field of protoconscious experience
("occasions of experience"). Abner Shimony7
observed that Whitehead's occasions were comparable to quantum
state reductions-actual events in physical reality (see below).
But what of Whitehead's "basic field" of protoconscious
experience? How could experience (qualia) simply exist in empty
What is empty space? This question also stems from ancient
Greece. Democritus argued that empty space was a true void whereas
Aristotle contended that it was in fact a plenum (background filled
with substance)-a medium in which heat and light traveled. Siding
with Aristotle, Maxwell's 19th century theory of the
luminiferous ether described a plenum that carried electromagnetic
waves. However attempts to detect the ether failed and Einstein's
special relativity in 1905 reverted to Democritus in that empty
space was an absolute void. However ten years later Einstein's
general relativity with its curved space and distorted geometry
reversed his stand to opt for a richly-endowed plenum termed the
Figure 1. Two descriptions of fundamental spacetime geometry. a) A quantum spin network. Introduced by Roger Penrose8 as a quantum mechanical description of the geometry of space, spin networks describe a spectra of discrete Planck scale volumes and configurations9,10. Average length of each link is the Planck length (1033 cm). b) Four dimensional spacetime may be schematically represented by one dimension of space and one dimension of time: a two dimensional "spacetime sheet." Mass is curvature in spacetime, and the two spacetime curvatures in the top of Figure 1b represent mass (e.g. a tubulin protein) in two different locations, or conformations respectively. In quantum superposition mass separated from itself is simultaneous spacetime curvature in opposite directions, a separation or "bubble" of spacetime. At a critical degree of separation, the system becomes unstable and must select either one state or the other2.
We now know that at very small scales space and time are not smooth,
but quantized. This granularity occurs at the incredibly small
dimensions of the "Planck scale" at 10-33
centimeters and 10-43 seconds. Roger Penrose portrays
this basic makeup of the universe as a dynamical spider-web of
quantum spins8. These "spin networks" create
an evolving array of Planck scale geometric volumes defining four
dimensional spacetime (Figure 1a). Penrose applies Einstein's
general relativity (in which mass equates to curvature, or perturbation
of spacetime) all the way down to this near-infinitesimal geometry
(Figure 1b). Thus everything is in reality particular arrangements
of spacetime geometry. Building on these ideas, Lee Smolin9,10
likens spin network volumes to Leibniz monads and suggests that
self-organizing processes at this level constitute a flow of time,
raising the issue of whether the universe is in some sense alive.
Could infinitesimally small, weak and fast processes be coupled
to biology? A reasonable possibility for such a link is Penrose's
objective reduction-a particular type of quantum state reduction
in which new macroscopic information emerges.
At the Edge of Reality: Quantum State Reduction and Consciousness
Quantum theory describes the bizarre wave/particle duality of
energy and matter at very small scales. The behavior is so strange
that the American physicist Richard Feynman once commented "anyone
who claims to understand quantum theory is either lying or crazy."
Strange as it is, quantum theory offers features which may be relevant to consciousness. One is that large collections of quantum particle/waves can merge into unitary coherent states of macroscopic size and influence. Superconductors, BoseEinstein condensates and lasers are unitary states in which component atoms or molecules give up individual identity and behavior. Such coherent quantum states have been suggested to occur among brain proteins to provide unitary "binding" in vision and sense of self11,12.
Another feature involves "quantum superposition." Components
of isolated small scale systems can exist in different states
or locations simultaneously. This is contrary to our perceived
macroscopic world in which objects have well defined positions
and are decidedly concrete. The problem is the transition-why
and how do microscopic quantum superposed states become classical
and definite in the macro-world? This problem is called quantum
state reduction, or collapse of the wave function, and it may
be the key to both consciousness and reality.
Experimental evidence in the early part of this century led great
theorists Bohr, Heisenberg and Wigner to conclude (the "Copenhagen
interpretation") that objects remain in wave-like quantum
superposition until observed by a conscious human being-consciousness
causes collapse of the wave function! To illustrate the apparent
absurdity of this conclusion, in the 1930's Schrodinger devised
his famous thought experiment Schrodinger's cat. A living cat is
placed in a box into which poison can be released by a quantum
event, e.g., sending a photon through a half-silvered mirror.
So after the photon has been sent there are equal possibilities
that the cat is either dead or alive. But according to the Copenhagen
interpretation until a conscious being opens the box to observe,
the cat is both dead and alive. Schrodinger's point was
that the conscious observer interpretation was incorrect.
Many physicists now believe that intermediate between tiny quantum-scale
systems and "large" cat-size systems some objective
factor disturbs the superposition to cause collapse, or "objective
reduction (OR)." According to Roger Penrose2,13
this objective factor is an intrinsic feature of spacetime itself
(quantum gravity). As mass is equivalent to spacetime curvature,
Penrose begins with the notion that quantum superpositionactual
separation (displacement) of mass from itself is equivalent to
simultaneous spacetime curvatures in opposite directions, causing
"bubbles," or separations in fundamental reality (Figure
1b). Penrose reasons that these bubble-like separations are unstable
and reduce to specific states and locations after a critical degree
of separation. If proto-conscious experience is rooted in the
Planck scale, then objective reductions (Whitehead's occasions
of experience) may ripple through an experiential medium.
Could OR events occur in the brain? The critical spacetime separation
precipitating Penrose's OR is given by the uncertainty principle
E=h/T. E is the energy of the superposed mass, h is Planck's constant
over 2pi, and T is the coherence time until reduction. The size
(and energy) of a superposed system (degree of spacetime separation)
is inversely related to the time T until selfcollapse. If
isolated, a large system (e.g. Schrodinger's one kilogram cat)
will undergo OR very quickly, e.g. in only 10-37 seconds.
A small system such as a single isolated superposed atom would
undergo OR only after 107 years. OR brain events would
be linked to neural processes with T in the range of tens to hundreds
of milliseconds (e.g. 25 msec intervals in coherent 40 Hz). For
T=25 msec (40 Hz) OR events, E corresponds to roughly 3 nanograms
(3 x 10-9 gram) of superposed brain mass.
Nanograms of what? Which biological structures could function
as both classical and quantum computers, avoid environmental decoherence
and couple to neural-level activities? Microtubules are the logical
Are Microtubules Quantum Computers? The PenroseHameroff
"Orch OR" Model
Interiors of neurons and glia are functionally organized by webs
of protein polymersthe cytoskeleton14. Its major components
are microtubules, actin and intermediate filaments. Microtubules
are selfassembling hollow cylinders whose walls are crystalline
lattices of subunit proteins known as tubulin. Evidence links
the neuronal cytoskeleton to cognitive functions, and theoretical
models suggest interactive microtubule subunits function as molecular
automata capable of nanosecond-scale computation (Figure 2a)4.
Schematic of neural synapse showing cytoskeletal structures within
two neurons. Left: Pre-synaptic axon terminals releases neurotransmitter
vesicles (black spheres) into synaptic cleft. Thick, black rod-like
structures at top indicate microtubules; thinner filaments (e.g.
synapsin) facilitate vesicle release. Right: Dendrite on post-synaptic
neuron with two dendritic spines. Microtubules in main dendrite
are interconnected by microtubule-associated proteins. Other cytoskeletal
structures (fodrin, actin filaments, etc.) connect membrane receptors
to microtubules. Based on Hirokawa14.
Roger Penrose and I have developed a model in which quantum superposition,
objective reduction and quantum computation occur in microtubule
automata within brain neurons and glia. Microtubuleassociatedproteins
(MAPs) provide feedback and "tune" the quantum oscillations;
the proposed OR is thus selforganized ("orchestrated"
objective reduction"Orch OR")15-21. In the
Orch OR model microtubule quantum computation is isolated from
decoherence (Box 1) and continues until threshold is met (E=h/T)
and an OR event occurs (Figure 2b). For example an OR event coinciding
with one 40 Hz cycle (T = 25 msec) would require E = 2 x 1010
superposed tubulins (roughly 20,000 neurons).
Quantum computation in the Orch OR scheme differs from technological
proposals in that superpositions in the latter will reduce to
output states by environmental decoherencecomputation is terminated
by intervention and choice of states has an element of randomness.
On the other hand, in the Orch OR scheme isolated superpositions
self-reduce due to instability in spacetime separation. The choice
of outcome states, according to Penrose, is therefore neither
completely deterministic nor random, but has an element of non-computabilityinfluenced
by Platonic logic embedded in spacetime. Penrose has also suggested
that aspects of human understanding and consciousness involve
non-computability, a controversial and widely assailed claim.
Although outnumbered by his critics, Penrose has thoroughly
and systematically answered them3. Non-computability
is a clue, a delicate thread with which to unravel the mystery
Orch OR and Cognition
Each proposed Orch OR event consists of 1) an isolated quantum computing phase identified with preconscious, implicit processing which culminates in 2) instantaneous reduction corresponding with a discrete conscious "now" event-a Whitehead "occasion of experience."
Each event selects (noncomputably) particular configurations
of Planck-scale experiential geometry and corresponding classical
states of microtubule automata which regulate synaptic/neural
functions (Figure 2; Figure 3a,b). Sequences of discrete conscious
events (e.g. at 40 Hz) can provide a "stream" of consciousness.
Orch OR events in conscious experience. a) (left) Three
tubulins in quantum superposition prior to 25 msec Orch OR After
reduction (right), particular classical states are selected.
b) Fundamental spacetime geometry view. Prior to Orch OR (left),
spacetime corresponding with three superposed tubulins is separated
as Planck scale bubbles: curvatures in opposite directions. The
Planckscale spacetime separations S are very tiny in ordinary
terms, but relatively large mass movements (e.g., hundreds of
tubulin conformations, each moving from 106 to
0.2 nm) indeed have precisely such very tiny effects on the spacetime
curvature. A critical degree of separation causes Orch OR and
an abrupt selection of single curvatures (and a particular geometry
of experience). c) Cognitive facial recognition. A familiar
face induces superposition (left) of three possible solutions
(Amy, Betty, Carol) which "collapse" to the correct
answer Carol (right). d) Cognitive volition. Three possible
dinner selections (shrimp, sushi, pasta) are considered in superposition
(left), and collapse via Orch OR to choice of sushi (right).
Consider Orch OR in the context of two cognitive tasks: facial
recognition and ordering dinner (Figure 3c,d). Each may occur
in a series of steps yielding intermediate solutions, however
for the purpose of illustration consider how single Orch OR conscious
events could accomplish these tasks. (Although classical neurallevel
parallel computation can partially explain these functions, the
Orch OR scheme provides far greater information capacity, conscious
experience, binding, and noncomputability consistent with
Imagine you briefly see a familiar woman's face (Figure 3c). Is she Amy, Betty, or Carol? All possibilities may superpose in quantum computation. For example during 25 milliseconds of preconscious processing quantum computation occurs with information (Amy, Betty, Carol) in the form of "qubits", superposed states of microtubule automata. As threshold for objective reduction is reached, superposed tubulin qubits reduce (collapse) to definite states, becoming bits. Now, you recognize Carol as a particular experiential geometry is selected! (Many more than three possibilities, in fact an astronomically high number of possibilities could be superposed in microtubule quantum computing.)
In a volitional act possible choices may be superposed. Suppose
you are selecting dinner from a menu. During preconscious
processing, shrimp, sushi and pasta are superposed. As threshold
for objective reduction is reached, the quantum state reduces
to a single classical state whose selection results from deterministic
quantum computation influenced at the moment of reduction by Platonic
logic embedded in the Planck scale. A choice is made. You'll have
The Orch OR model is consistent with known neurophysiological
processes, generates numerous testable predictions18,19 and
is the type of multi-level, trans-disciplinary theory required
to address the mind's enigmatic features. Consciousness may involve
subtle links between the brain and fundamental spacetime geometry.
to Roger Penrose for collaboration and insight, to Carol Ebbecke
for expert technical assistance, and to Dave Cantrell for artwork.
Discussions with Scott Hagan and Avi Elitzur are also appreciated.
Keywords consciousness, qualia, quantum theory, spacetime geometry, free will, microtubules, cytoskeleton, reality, orchestrated objective reduction, quantum computation, cognition, facial recognition, panpsychism, superposition
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Isolated Macroscopic Quantum States in the Brain?
At first glance the brain is a noisy, thermal environment, hardly hospitable to delicate quantum effects which require (in the technological realm) extreme cold to prevent thermal excitations and environmental decoherence. However nature may have solved the problem of quantum state isolation. For example Dan Sacketta of NIH has recently shown that microtubules may be insulated from thermal noise by a surrounding sleeve of plasma-like charge condensation.
Another protective mechanism may isolate microtubule quantum superposition by phases of actin gelation. Among the most primitive of biological activities are "solgel transformations." Cytoplasm within living cells alternates between phases of 1) "sol" (solution, liquid), and 2) "gel" (gelatinous, solid) caused by disassembly (sol) and assembly (gel) of cytoskeletal actin (regulated by calcium ion). Solgel transformations play essential roles in neurotransmitter vesicle releaseb,c, can occur rapidly (e.g. 40 cycles per second) and be deformable without transmitted responsed. Cyclical encasement of microtubules by actin gels may be an ideal quantum isolation mechanism, suggesting a biphasic cycle of microtubule computation: 1) a "sol" liquid, communicative phase of classical computation, and 2) a "gel" solid state, isolated quantum computing phase. Feasibility of quantum coherence in the internal cell environment is supported by the observation that quantum spins from biochemical radical pairs which become separated retain their correlation in cytoplasme. Key quantum events may also be shielded either in hollow microtubule cores or intra-protein hydrophobic pockets (where anesthetic gases are known to act).
But how could isolated cytoplasmic quantum states traverse membranes and synapses to occur macroscopically among microtubules in (e.g. 20,000) neurons throughout the brain? One possibility involves quantum tunneling through gap junctions, primitive electrotonic windows between neurons and glia. Neurons interconnected by gap junctions form networks which fire synchronously, "behaving like one giant neuron"f (possibly accounting for synchronized 40 Hz neural activityg). Unlike chemical synapses which separate neural processes by 3050 nanometers, gap junction separations are 3.5 nanometers, within range for quantum tunneling. Gap junctions are widespread but unevenly distributed. Immunolabeling of gap junction protein (connexin) precursor demonstrates high levels in thalamic subnuclei, layers 2 and 3 of cortex, and midbrainh. Thalamocortical networks of gap junctionconnected neurons with sol-gel phases coupled to synchronized 40 Hz activity could isolate microtubules across large brain volumes and provide cycles of isolated macroscopic quantum coherence.
Figure Schematic sequence of phase of actin gelation/quantum isolation (13) and solution/environmental communication (4) around MT. Cycles may occur rapidly, e.g., 25 msec intervals (40Hz).
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