HOW does a wrinkled lump of grey matter weighing little more than a kilogram
manage to think, love, dream and feel such widely different sensations as raw
pleasure and numbing depression? Philosophers, physicists and computer modellers
have been pondering these questions for decades, wondering how your brain
creates your consciousness—your personal inner world of thoughts and
feelings.
Thus far, their deliberations have not been entirely fruitful. My own view is
that we should put this big question—the “water into wine” problem of how
the bump and grind of brain cells translates magically into subjective
experience—to one side for the moment, and concentrate on a much less
glamorous approach. I think we can try to establish a correlate of
consciousness—the particular physical state of the brain that always
accompanies a subjective feeling. If we could do so we may at last be ready to
develop a testable model of what happens in the brain when you are
conscious.
My suggestion is that the depth of consciousness varies according to the
number of brain cells working together at any moment in time. At its most basic
level I am proposing that consciousness is synonymous with raw emotions, and at
its fullest extent with inner reflection and self-awareness. Consciousness is
like a dimmer switch, it grows as brains grow, but it also varies from moment to
moment as neurons are coordinated into vast but highly evanescent working
assemblies. These assemblies are modified in turn by feedback from the body, and
communicate their state to it. Hence, consciousness, in my view, is also a
dialogue between the three great control systems in the body: the nervous,
hormonal and immune systems.
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Soon we may even be able to monitor this dialogue, or at least to measure
these assemblies as an index of consciousness, and so perhaps gain a better
understanding of what other people or animals are experiencing. Most usefully,
this model might also suggest new ways to treat mental illnesses, many of which
I see as caused by an inappropriate degree of consciousness at any one time.
The best way to begin to explain consciousness is to draw up a shopping list
of the features or properties we expect. Then neuroscientists can go back to
their labs and see how the brain could deliver.
First, I don’t believe we should be looking for one special brain region.
Many regions are active while you are awake, but as you become unconscious, they
all shut down in a fairly uniform way. When someone has been anaesthetised,
there’s no one region that lights up or gets extinguished. There is no single
specialised “centre for consciousness”.
Secondly, although consciousness comes from more than one brain area, at any
one moment you have only one consciousness. The world seems of a piece. So we
can expand the first item on the list to say that while consciousness is
distributed all over the brain, somehow the activities of the different regions
are coordinated. And if there’s no special centre or neurons for consciousness
then the neurons and areas that generate it must do other jobs as well. The
physical manifestation of consciousness must be something that happens in or to
ordinary brain cells at certain times, but not others.
Also on my shopping list is the notion that the more complex the brain the
deeper the consciousness. The idea of degrees of consciousness helps answer
questions such as when a fetus becomes conscious, and which other animals are
conscious. I can’t see a physical Rubicon when the brain of a developing fetus
changes suddenly, nor any obvious cut-off in the animal kingdom between a
nervous system that generates consciousness and one that does not. We should
think instead of a continuum: a rat is conscious but not as conscious as a dog;
a dog is conscious but not as conscious as a primate; and so on. Even an ant
will have a tiny modicum of consciousness.
If you think of consciousness like this—as something that varies by
degree—there are two interesting consequences. The first is that we may be
more conscious at some times than at others, hence our experience of states of
“heightened awareness”, and the conviction that we can “raise” or “deepen” our
consciousness. The second, crucial consequence is that we will have finally
converted consciousness from a qualitative to a quantitative phenomenon. We can
then look for a measure of the depth of our consciousness as it varies from one
moment to the next, and search the brain for something that contracts or expands
with it. I think that the most logical place to look is in very large
networks—”assemblies”—of brain cells.
You’re born with pretty much all the brain cells you’ll ever have, but as you
mature these cells develop more interconnecting branches. Our brains are
incredibly plastic, and these connections grow and change with every experience.
Babies evaluate the world in purely sensory terms—how sweet, how fast, how
cold, how loud. But gradually these abstract sensations coalesce into people and
objects with meaning and associations. It’s these personal connections and
associations that I think of as the “mind”. The mind is your personalised brain,
which allows you to see the world in terms of what you have experienced already.
Even if you’re a clone—that is, an identical twin—your mind will be
unique. You see the world in terms of things that have happened to you
alone.
If we see a familiar person, our visual system activates a “hub” of brain
cells that corresponds not only to the shapes, movements and colours of a face,
but to all the associations set up in our mind by our experiences of that
person. That can all happen without our being aware of it. Consciousness, I
believe, is generated as this active, hard-wired hub corrals huge numbers of
other brain cells around it to form a vast working assembly that lasts for just
a trice. The image I have is like throwing a stone into a puddle, producing
ripples of consciousness.
We now know the brain to be capable of forming such highly transient
assemblies. Amiram Grinvald at the Weizmann Institute in Rehovot, Israel, has
shown that in response to a flash of light, as many as 10 million brain cells
become active together, coordinated into a working assembly that lasts for less
than a quarter of a second—exactly the space and time scales I think we
should be exploring.
The assembly will be slightly different every time. Partly it will depend
upon the size and strength of the stimulation of the hub, but also on the levels
of a variety of chemical messengers—neurotransmitters—which change
moment by moment. These transmitters “modulate” the activity of large groups of
cells and mediate arousal levels, your sleep-wake cycle and your dreaming. In
physiological terms, these put cells on “red alert”—they can predispose
brain cells to be recruited into the working assembly, triggering lots of covert
associations.
I think it is the activity of these transient neuronal assemblies that
correlates with the depth of your consciousness at any one moment. To test the
model, let’s take some examples of the different types of assemblies formed and
see how they relate to different types of consciousness.
One time you’d expect to see unusually small cell assemblies would be when
you didn’t have much connectivity in the first place, as in a young child’s
brain. What do we know about an infant’s consciousness? One feature is that
their centre of attention varies depending entirely on the sensory quality of
what they’re seeing. They live in the press of the moment, in a rather abstract
world with little meaning, reacting to everything in a simple, emotional way.
Infants are like little sensory sponges: they lack any accumulated experience
with which to interpret the world. They haven’t yet forged multiple
connections—they haven’t yet developed a “mind”. Each burst of brain
activity will come from only a small hub of cells, which will create small,
short-lived ripples of consciousness.
This is, I believe, the most primitive kind of consciousness we have, with a
small assembly associated with strong emotions and an immature mind. So my own
view is that emotions are the building blocks of consciousness, and that you
can’t have consciousness without some sort of emotion. That’s why I for one
don’t put much of a premium on computer models of consciousness: such models
focus on tasks such as learning and memory, which an ordinary PC can do without
subjective inner states.
There are times when adults too have diminished consciousness. You would have
small assemblies, as in childhood, when you’re dreaming. However, the reason
would be different. In this case you have no strong sensory input, so there’s
little to stimulate the neuronal hubs, and you’re dependent on internal residual
neuronal activity. This perhaps explains why dreams have a disconnected, flimsy
narrative. At the time they seem very real, with high emotional content, but in
retrospect we wake up and judge our dreams as irrational with the checks and
balances of our cognitive adult minds.
We can chemically alter our level of consciousness, too. So a third situation
in which you might have a small assembly would be if the work of the brain’s
chemical messengers was disrupted, affecting the ease with which the working
assemblies formed. Taking drugs such as ecstasy can interfere with one such
chemical, serotonin. And in schizophrenia, levels of another messenger,
dopamine, are effectively in excess. In both cases the ease with which
assemblies form would change, the net size would be smaller and consciousness
would seem childlike or dreamy. People may take the world at face value, see it
in sensory terms and display flimsy logic.
Another time you would find only small assemblies is when you are in a
rapidly changing environment with such competition that the assemblies don’t
have a chance to form properly. Fast-paced sports like white-water rafting,
bungee-jumping or skiing would do it, as would a rave.
The opposite of such states would be a large cell assembly, where one would
expect the outside world to seem remote. Your senses would be reduced, you might
feel emotionally numb, yet extremely self-conscious. You would have a highly
logical, perhaps persistent train of thought. These symptoms often occur in
clinical depression. Perhaps depression is due to the malfunctioning of the
chemical modulators, resulting in overly large assemblies. We know the drug
Prozac and related agents influence those chemicals.
Although my theory seems to predict what to expect in different types of
consciousness, the assemblies of neurons I’m positing do not all on their own
generate consciousness. Assemblies are merely an index—a correlate of your
prevailing inner state. Something else must happen. I believe assemblies report
to the rest of the body, and the rest of the body reports back to them, and this
iteration somehow translates into subjective consciousness.
Neuroscientists, at their peril, often ignore the fact that the brain is in a
body. We know that feedback from the rest of the body—most noticeably the
immune system and hormones—can influence our state of mind, and similarly
our state of mind can influence other control systems like our immune status.
And we know that the nervous, endocrine and immune systems are interlinked. I
think the links must be chemical, and for my money peptides are very good
candidates. These substances coexist with traditional transmitters, but are only
released under special circumstances, as neurons become more active. There are
many different peptides, so you would never have exactly the same amounts or
combinations twice. Moreover, we know that peptides can interface with the
immune, nervous and endocrine systems: some peptides are also hormones, and this
puts them in a good position to be, if you like, trilingual.
The way I see it is that at any one moment, transiently formed cell
assemblies would release a signature profile of peptides into the body. These
peptides influence the endocrine and immune systems, and in return the systems
would release peptides that would determine the size of the brain assemblies.
That iteration of peptides between the three great control systems of the body
is, in my view, what happens when you are conscious. One day it may be possible
to test this hypothesis, by recording profiles of peptide availability in the
blood and trying to correlate these with the prevailing state of
consciousness.
I think at a clinical level this exercise would be useful. It might suggest
new ways of treating conditions such as depression with novel types of drugs, or
of developing non-drug treatments that might drive the formation of a certain
size of assembly and alter the type of consciousness in a beneficial way.
How this all translates into the elusive subjective inner state of
consciousness is a completely different question, and I’m not pretending to have
answered it. On the other hand, I do think that we can use this model in the
future to design experiments and help us understand depression and emotions, why
people take drugs, and perhaps most mystifyingly, why people go
bungee-jumping.
WHAT is the key to the perfect state of mind? Growing up and acquiring an
adult mind brings both curses and benefits. Without it we would only see the
world in terms of infant-like abstract sensory qualities, without context or
meaning. But equally our adult mind can be the kiss of death for pleasure.
We use some telling phrases—”letting ourselves go” or getting “out of
our minds”. Whether it’s through drugs, fast sports, dancing or loud music, we
enjoy being out of control—the passive recipient of our senses. The word
ecstasy comes from the Greek ekstasis, meaning to “stand outside
dzܰ”.
But while the conscious experience may be thrilling, self-consciousness that
you are happy is something that occurs “off-line” once you have regained your
“mind”. This fulfilment is as important as passion. The trick is being able to
turn your level of consciousness up and down. If you’re stuck in a deeply
non-sensory state, we call it clinical depression. People with schizophrenia, on
the other hand, may be excessively influenced by their senses and the outside
world. An inappropriate switching between the two extremes might be manic
depression. We need to let our hair down and let our minds go, but we also want
more—a sense of fulfilment and the chance to reflect on pleasurable
experiences. For that you need the checks and balances of an adult mind. A
perfect life is a balance between the two extremes.
If you’re happy and you know it…
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Further reading:
The Private Life of the Brain
by Susan Greenfield is published by Penguin (2000)