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David Chalmers, a philospher from Washington University, jokingly calls
it the law for the minimisation of mysteries. ‘Consciousness is a mystery,
quantum mechanics is a mystery. When you have two mysteries, well maybe
there is really only one. Perhaps they are the same thing.’

That the answer to consciousness might be found in the strange world
of the quantum is a suggestion that dates back at least as far as the musings
of physicist, David Bohm, in his 1951 book, Quantum Theory. In the past
few years, however, such speculation has taken on a new urgency. What else,
ask a host of thinkers, including Roger Penrose, the Oxford mathematician
famed for his work on the geometry of tiling patterns and black holes, could
explain aspects of the mind such as free will, intuition, creativity and
the subjective unity of experience?

In the odd world of the quantum, things appear to exist in a multitude
of states – describable only as the set of probabilities known as a wave
function – until tipped into a definite outcome by an act of ‘measurement’.
An electron or atom (and some would even argue the whole Universe) remains
an open field of possibilities until forced into an interaction. It is as
if the physical world wants to explore many alternative pathways before
collapsing into a settled state. For the champions of quantum consciousness,
this seems to be just what the creative human mind does: sample many paths
and outcomes before its ‘wave function’ collapses into the coherent state
which is our logical stream of thought. The difficulty for quantum theorists
has been that while they may have found the parallels attractive, their
ideas lacked an experimental basis and also went against common sense.

Most neuroscientists and philosophers of mind now believe that consciousness
will be explained by the neural connectionist hypothesis. This sees the
mind as the outcome of patterns of impulses dancing across the synaptic
connections that make up the neural circuits of the brain; a tangled web
of information rather than a special field or unknown force.

What gives the connectionists confidence is that any interference with
the functioning of the brain’s 50 billion nerve cells – whether from strokes,
drugs, the surgeon’s knife or merely sleep – tends to alter subjective experience
in a rather definite way. In other words, breaking or altering connections
can produce predictable effects on behaviour. By contrast, there seems to
be no obvious way that quantum effects could play any part in brain activity.

‘The scale’s all wrong. How can something that occurs at the subatomic
level influence events at the macroscopic level of the cell, where we already
know something is happening?’ asks John Taylor, a physicist from King’s
College London who is pursuing a connectionist model of consciousness. Taylor
says that in the hot, sticky world of the brain, any fleeting quantum events
that might carry information would be drowned out in the hubbub of background
thermal noise. While neural networks are known to be robust to such noise,
a quantum-based ‘mind design’ seems to demand a degree of biochemical precision
that is utterly at odds with messy organic systems.

In two minds

Such views led many to instantly dismiss the rash of quantum speculation
that arose in 1989, largely in the wake of popularising books by Penrose
and also Michael Lockwood of the University of Oxford and author Danah Zohar.
Indeed, for a couple of years the field went relatively quiet. But this
year the bandwagon has started to roll again. Penrose has written a sequel
to the Emperor’s New Mind called Shadows of the Mind, which extends his
ideas and is due out this autumn. But supporters of a quantum explanation
claim that they have a site where quantum effects may be taking place.

In the past, quantum enthusiasts could be accused of merely lumping
together two unfathomable mysteries. What they needed was a plausible mechanism
through which quantum-level phenomena could have an effect on higher-level
brain activity. Earlier this year, at a conference on the mind at the
University of Arizona at Tucson, quantum enthusiasts argued that they had
discovered their missing link – cell structures called microtubules.

Judging from the dismissive responses of other delegates, the enthusiasts
still have a long way to go if they are to make any converts. The quantum
theorists, said Taylor, were guilty of piling speculation upon speculation.
Here, we look at some of their ideas and examine why they are so reviled.

Microtubules are the lattice of protein rods which fill every cell in
the body, creating an inner scaffolding or cytoskeleton. Each microtubule
is a hollow cylinder, 25 nanometres across, built from 13 strands of the
protein tubulin. Microtubules are a common building material in the cell
and clusters often form larger structures such as the beating cilia that
cover the surface of some cells or the centrioles which organise cell division.

Before microtubules were discovered in the 1970s (previously, the fixatives
used in electron microscopy had been dissolving them), biologists tended
to think of cells as watery bags with a few organelles slopping about in
a soup of enzymes. But it is now clear that cells have a well-organised
skeleton made out of microtubules. This cytoskeleton not only gives cells
a shape, it also appears to play a key role in the circulation of proteins
and plasma products. Each microtubule sprouts a coating of thread-like microtubule
associated proteins (MAPs) which some researchers believe form contractile
spurs that drag plasma along, ‘hand over hand’, in a miniature bucket brigade.

Cell biologists feel they have only just begun to scratch the surface
of the part played by microtubules. Yet quantum theorists have been quick
to seize upon them as structures of exactly the right scale to act as amplifiers
of submolecular quantum effects. A number of speakers at the Arizona conference
shared the conviction that microtubules might form the ultimate substrate
for consciousness – although their actual theories varied wildly. These
ranged from the idea that microtubules might generate a coherent electromagnetic
field which structures the water trapped inside each protein cylinder to
the possibility that microtubules act as waveguides to photons – and so
form a tiny optical computer inside each cell.

The person most responsible for this flurry of speculation about microtubules
is Stuart Hameroff, an anaesthesiologist at the University of Arizona who
has toyed with at least half a dozen variations of the story. Hameroff says
regardless of whether microtubules prove to be harnessing quantum effects,
he is convinced they must play some part in any final explanation of consciousness.
He points out that even single-cell animals such as the slipper-shaped paramecium
have primitive sensory and learning capabilities. With practice, paramecia
can learn to back more quickly out of narrow glass tubes. Hameroff says
other experiments suggest they can even learn paths through simple mazes.
Yet paramecia have no synapses or brains. Something – Hameroff believes
microtubules – must be organising their behaviour.

Complex ripples

One idea that Hameroff has developed with colleagues, including Steen
Rasmussen of the Los Alamos National Laboratory, is that the surface of
microtubules could ripple to act as a cellular automata computer. A cellular
automata is a grid of cells where each cell switches its neighbour on or
off to create complex – and self-organising – patterns of activity.

Hameroff says that each protein molecule making up the strands of a
microtubule wall is a C-shaped building block. He believes these blocks
can vibrate rapidly, in the order of a nanosecond, and if coordinated, this
contraction and expansion could send a meaningful flow of information down
the flanks of each microtubule. So within each neuron – indeed, within every
cell – there might be a miniature connectionist network carrying out its
own level of information processing.

The cellular automata theory originally seemed to have no need for a
quantum dimension. But a big problem was that some sort of time-keeping
clock or long-range force was necessary to keep all the protein shape changes
in step, otherwise any patterns would quickly be washed away. After a few
oscillations, the patterns would degenerate into randomness.

Rather than giving up on what looked to be a rather implausible line
of speculation, this difficulty led Hameroff to the controversial work of
Herbert Frohlich, a physicist at the University of Liverpool. In the 1970s,
Frohlich suggested that what drives the vibration of a protein molecule
could be an internal oscillating dipole. That is, strategically placed at
the hinge point of a large molecule might be a single trapped electron or
region of electrostatic charge. When this trapped charge made a quantum
flip-flop shift of position – a quantum leap across the barrier of the hinge
to a point on the other side – it might be enough to throw the whole protein
into a different shape. Frohlich went further and proposed that cell membranes
might create a situation where a whole series of such delicately poised
dipoles lined up – like compass needles in a magnetic field – leading to
a quantum coherent state on the macroscale.

Such long-range alignment, producing a single quantum system covered
by the same wave function equation, is well known to physics from phenomena
such as lasers and superconductivity. But most scientists dismiss the idea
that the same kind of coherence can be achieved in the hot, messy realm
of organic chemistry. Undeterred by what seems to be a common-sense argument,
Hameroff claims that microtubules might just have the right dimensions
and quasicrystalline structure to generate the fleeting regions of quantum
coherence needed to keep vibrating tubulin molecules in step, making the
cellular automata idea theoretically plausible.

Leaping ahead to how cellular automata computations would lead to conscious-level
processes, Hameroff says thoughts and men-tal images may emerge when the
coherence between the patterns rippling along the walls of a network of
microtubules reaches a certain critical level. Memories could be retained
as ‘frozen’ standing wave patterns on the surface of microtubules. Creative
thought and intuition would exploit the clusters of microtubules often found
lying in parallel in cells – quantum superposition allowing a cluster to
exist in many states before collapsing into a favoured solution.

Hameroff admits that attributing such powers to microtubules leads to
the conclusion that paramecia – or even the cells in your big toe – are
in some sense conscious. But he says that brain cells are known to have
unique forms of microtubule organisation and the structure of the brain
probably also makes a big difference to the overall properties of the system.
The higher abilities of the human mind would only emerge once microtubules
were put together in the right way.

Foot in two camps

As if the cellular automata theory of consciousness were not startling
enough, Hameroff has a foot in several other quantum camps. Another line
of speculation is that microtubules form wave guides for channelling photons.
Again, Frohlich-like states of quantum coherence are needed to create the
right conditions. In this case, water inside the tubule – or possibly bound
tightly to the tubule’s outer surface – becomes aligned with the quantatised
electromagnetic field.

Hameroff claims that there is enough physical theory to suggest that
in such a structured state, the water will emit photons and that these will
propagate down the microtubule without absorption, making use of properties
dubbed superradiance and self-induced transparency. Superradiance emerges
from the highly speculative theory that tightly confined water molecules
will spontaneously line up, turning some of their chaotic thermal energy
into coherent, laser-like, pulses of light. Self-induced transparency is
the still more unlikely idea that these photon pulses would not immediately
be reabsorbed by neighbouring water molecules but would pass down the tube
relatively unhin-dered because – like light bouncing down a fibre-optic
cable – the microtubule walls would act as a conducting waveguide. In effect,
the cytoskeleton becomes an optical computer, flashing messages across the
cell via laser-like beams of light.

The reaction of other scientists at the Arizona conference was mixed.
A few had come thinking quantum theories were rubbish and now had to admit
something interesting might be happening down at the microtubule level.
However, many more departed still thinking quantum theories were rubbish:
there might be a lot unknown about the role played by microtubules in cell
functioning, but there was no reason to think that microtubules were harnessing
quantum effects to create consciousness.

Heated discussions broke out in private, with critics accusing the quantum
camp of being too eager to treat speculation as established fact. Most of
the important phenomena on which the microtubule theories were based, such
as structured water superradiance and Frohlich’s macroscale coherence, were
themselves of dubious standing. Shaking his head during a coffee break,
Jack Tuszynski of the University of Alberta said he was one of many physicists
who searched for evidence of Frohlich-type effects during the 1980s and
found nothing.

Meanwhile, Taylor echoed several others in saying it was bad science
when it became hard to tell the joins between the parts of a theory which
were based on established knowledge and the parts which were still guesswork.
Even more worrying for some was the apparently poor grasp of basic biology
among many of the quantum proponents. John Watterson, a biologist from Griffith
University in Australia, said it became clear in conversation with one leading
figure that he did not know proteins were made up of amino acids: ‘I was
really rather shocked by that.’ In another telling incident, a psychologist
confided that he had once shown a quantum physicist around his laboratory
who mistakenly assumed that nerve cells communicate with electromagnetic
waves and electrons. It had never occurred to him that they might use chemical
neurotransmitters.

A second common criticism was that a quantum level explanation of consciousness
was not even necessary. The unique features that seem to demand this type
of theory – such as the apparent coherence of subjective experience and
freedom of thought – could actually be supplied by the neural connectionist
approach. Free will and unity of experience are not the simple, structureless
characteristics they are often made out to be, said Christof Koch of the
Californian Institute of Technology, who collaborates with Francis Crick
in the search for a connectionist model of mind.

Despite such reservations, the Arizona conference does appear to have
put the quantum approach on the scientific map. Eric Harth, a physicist
from Syracuse University and leading neural connectionist, was moved to
comment that however plausible or implausible people might find the various
quantum theories, at least testable hypotheses were now being put before
the scientific community. Another more critical conference-goer remarked:
‘Before it was all just mystical hand-waving. Now they’ve given us something
concrete to shoot at.

John McCrone is a science writer working on a book about the new theories
of mind.