For a long time, universities
acted as if it were in bad taste to treat consciousness
as a subject for serious scientific research.
But gradually, in the 1980s, and then especially in the 1990s,
as brain-imaging technologies became increasingly accessible,
came to be recognized as a subject for multidisciplinary research.
And now, in the first decade of the 21st century, the study
of consciousness has become a highly dynamic field, one that
of course still involves a great deal of speculation and
of explanatory theories very few of which are
likely to stand the test of time in their current form.
we ever be able to achieve a satisfactory explanation
of consciousness? Some authorities doubt
it, and say that the origin
of consciousness is so complex that the human
brain would have no more chance of comprehending it than
an earthworm would have of understanding an ape.
But even if this doubt persists, we
must still try to identify the various
properties of consciousness so that we can better
define it, because so many clinical and ethical issues are
affected by the definition that we adopt. One obvious example
is the difficulty of determining the degree of consciousness
of patients who are in a coma,
and the sometimes hard choices that result. Two other examples
are the degree of consciousness that we ascribe to various
animals and to human fetuses
at the various stages of their development, because
some very real ethical
choices depend on our ability to judge their
state of consciousness. Such examples demonstrate the legitimacy
of research on this subject.
WHAT IS CONSCIOUSNESS?
What is consciousness? One way to try
to define this so familiar yet so mysterious phenomenon is to
try to state what it is not. In other words, when is someone
no longer conscious? In one
sense, it could be simply when they close their eyes and thus
lose their conscious visual experience. In another sense, it
could be when the dentist gives them an anaesthetic before pulling
a tooth, so that they lose their consciousness of pain.
Consciousness is also what we lose when
we fall asleep. But here things get more complicated right
away, because we are conscious of our dreams.
Despite their lack of coherence and their sometimes fantastic
features, dreams often feel like intense conscious experiences.
So we might say that is only when we reach the stages
of deep sleep that we truly lose consciousness. And even
then, it would be more accurate to say that we have very little
consciousness, rather than none at all—for example, a
mother may still hear her child crying even when she is in
Many characteristics of what we call
consciousness are also gradually lost by people suffering from
Alzheimer’s disease. They become detached from everything
going on around them and are no longer even sure of their own
identity. And there is something even more disturbing about seeing
someone in a coma after
a traumatic brain injury, because there is a body, obviously
alive, yet displaying no manifestations of consciousness.
If we try to
define consciousness a bit more directly, the first problem
that arises is that a conscious experience is truly accessible
only to the person who is experiencing it. And if you have
ever tried to express the content of one of your conscious
subjective experiences verbally to someone else, you know how
hard it is to do so clearly and reliably. This is the problem
of the “qualia” or
the phenomenological dimension of consciousness.
Another problem is that we
use the word “consciousness”with many
different meanings. This constitutes a sizable obstacle
to the study of consciousness, though some of the differences
are mainly differences
of degree rather than of kind. Nevertheless, when we talk
about consciousness without specifying which of its many manifestations
we are referring to, we are courting confusion. Here are some
of the meanings that we give to the word “consciousness”:
And as if all these senses of the word were
not enough, we also talk about “raising the consciousness”of
our fellow citizens, with regard to political issues, for example.
In this instance, the reference is to what is generally called moral
develops during childhood, but also whenever the focus of our
attention shifts from ourselves to other people, or to our species
as a whole, or to the entire planet.
The following joke summarizes
the position of an idealist on the relationship between mind
“What is mind? No matter. What is matter? Never mind.”
Are animals conscious?
Are computers conscious, or might they become so some day?
The only way that dualists can answer these questions is
by saying that lower animals and machines cannot be conscious
unless they possess a mind, the non-material substance that
dualists associate with consciousness. But how can anyone
Materialists see things differently, because they don’t
believe in any special “other substance” constituting
the mind in humans or any other beings. Materialists believe
that there are only physical processes in the brain, and
that some of these processes give the person whose brain
it is the feeling of “what
it is like to be” who they are.
Unlike the dualists, who are trapped in a yes-or-no logic
as to whether their “other substance” is present
or absent in any given animal or machine, the materialists
thus see consciousness
as a continuum.
Viewed this way, humans, apes, and cats clearly share a
certain form of consciousness. But rocks, seeds, and bacteria
probably do not have any consciousness. Between these two
extremes, however, there may be a whole spectrum along which
consciousness exists in varying degrees.
PHILOSOPHICAL POSITIONS ON CONSCIOUSNESS
The subjective nature of human consciousness
has long intrigued and fascinated the world’s great thinkers.
Long before scientists began to talk about the “hard
problem of consciousness”, many philosophers had
tried to explain how subjective consciousness fits into the
objective world. This inquiry
has given rise to many different philosophical traditions,
each with its own conception of the relationship between the
mind and the body, grounded in the particular broader vision
of reality that each of these traditions embraced.
Telling the story of each of these
traditions would take too much time here, so instead we will
simply summarize four of them that have had their proponents
throughout recorded time: idealism, dualism, materialism, and
Idealism holds that
nothing exists in the world except our conscious experiences.
Idealists therefore regard the material world as a mere illusion
of our consciousness.
George Berkeley (1685-1753)
In the radical form proposed by English
philosopher George Berkeley in the 18th century, idealism
pre-emptively solves the difficult problem of the interaction
between mind and matter by stating that mind is everything
and there is no matter. This position seemed such an affront
to common sense that it was even rejected by many of Berkeley’s
contemporaries. It goes against the realism that is the basis
for any scientific method. And yet idealism is hard to disprove
completely: any tangible evidence of the physical world can
always be interpreted as an impression of the world of the
mind. Moreover, idealism offers some seductive philosophical
advantages that have influenced an entire tradition of thinkers,
including Hegel, Schopenhauer, Husserl, and Bergson.
Dualism is the philosophical
tradition embraced by those who wish to reject neither the existence
of the material world nor the existence of the mind. Dualists
believe that there are two worlds: one of mind, and one of matter.
But dualists must then explain how a life of the mind is possible
in a body of flesh. Which raises a question that poses great
difficulties for dualists: the possible interaction between these
championed in ancient times by Democritus, Epicurus ,
and Lucretius, holds that there is nothing in the world
besides matter. Like idealism, then, materialism is a form
of monism—a philosophy that accepts the existence
of only one substance—but in this case that unique
substance is matter. Accordingly, materialists view subjective
consciousness as nothing more than the product of the interactions
among the neurons in the human brain. For the most radical
materialists, once we have successfully described the operation
of all of the cerebral processes that are the source of
the various components of consciousness, we will have said
everything there is to say about it.
Democritus (circa 460-370
Mysterianism, for its part,
argues that there probably is no solution to the problem of subjective
consciousness and that it will always remain a mystery to us. People
who adopt this stance believe that our sense of uneasiness in dealing
with the hard
problem of consciousness may be due to the limited cognitive
capacities of our brains. Hence, the reason that we can’t
imagine how neural activity can produce subjective feelings would
be the same as the reason that we can’t hold 100 numbers in
memory or visualize 7-dimensional space: the cognitive limits
of the tool with which we think.
Though Edward B.
Titchener is regarded as having been a structuralist
psychologist—one who focused on the structure of
the associations among mental phenomena—he recognized
that psychology could be studied from a functional perspective
as well. This latter approach was favoured by psychologists
such as William James.
received support from some philosophers. Gilbert
Ryle (1900-1976), for example, considered the concept
of individual subjectivity incoherent and derided it as “the
myth of the ghost in the machine”. The most
Ryle would concede was that our behaviours might have some
mental attributes, in other words, simple predispositions
to act in one way rather than another. Ryle described this
position as logical behaviourism.
Ludwig Wittgenstein (1889-1951) was another
logical behaviourist philosopher. He argued that public verification
of mental states is essential for human language to function.
A language whose statements could be verified only by one
person would have no meaning. Consequently, for Wittgenstein,
our statements about our subjective mental states mean nothing,
because they are verified only by ourselves.
To illustrate this point about personal subjectivity, Wittgenstein
used an analogy that has since become famous. He described
a world in which every person had a box that contained what
he or she called a beetle, but only that person could look
inside it. The actual contents of everyone’s
boxes might be completely different, or they might contain
nothing at all. In short, for Wittgenstein, for our minds’ contents
to have any objective value, they must be connected with
behaviours that render them directly observable.
THEORIES OF CONSCIOUSNESS IN THE COGNITIVE
Around the middle of the 20th century,
a number of major figures in fields such as psychology, computer
science, linguistics, anthropology, mathematics, and neurobiology
held a series of conferences in New York City, with an ambitious
goal: to pool their knowledge to create a new interdisciplinary
science that could explain the many facets of the human mind.
What emerged from these meetings
are now called the cognitive sciences, and
their stated purpose is to combine the data from numerous disciplines
so as better to understand such diverse phenomena as perception, language,
reasoning, and consciousness.
Before discussing the major currents
that have emerged in the cognitive sciences, let us briefly
review the historical context in which they emerged. As we
have just seen, the question of how the human mind functions
and what relationship it has to the brain and the rest of the
body has preoccupied thinkers for many years, and many
philosophical approaches to this question have been proposed over
In the 19th and early 20th centuries,
there was a school of psychology known as structuralism, represented
by such figures as Wilhelm Wundt and Edward
B. Titchener. The structuralists used introspection
to attempt to describe the elementary components of the human
mind. For example, according to the structuralists, a sensory
perception was based on the structure of the associations between
numerous sensations (whence the name “structuralism”).
The structuralists believed that
by describing the possible combinations of these elements,
they could deduce laws as general and powerful as those governing
the physical world. The structuralist approach was criticized
not only because of its implicit dualism,
but also because of the difficulty of experimentally testing
the introspection on which it was based.
In response, another school of thought
emerged that was radically opposed to structuralism. This school
was known as behaviourism. According to its
pioneers, such as John B. Watson and B.
F. Skinner, no scientific approach to psychology could
be built on subjective states, which are essentially private.
In contrast, their new psychology would be based not on personal
judgments about feelings and states of mind, but solely on
the experimental study of behaviour.
To make psychology a true science,
the behaviourists decided to study only observable phenomena:
the stimuli to which an organism is subjected, and the responses
that it makes to these stimuli. The behaviourists thus treated
the brain as a “black box”, in the sense that
they regarded what happened inside it as being unobservable
by its very nature.
With unobservable mental processes thus
excluded from the field of scientific psychology, notions such
as consciousness and the concepts associated with it became devoid
The behaviourists did, nevertheless, make
many useful discoveries, in particular concerning the operant
conditioning of behaviour, in experiments with rats and pigeons.
Obviously, this school of psychology was extremely focused on
the influence of our environment on our mental processes. Watson
even went so far as to state that the human mind is shaped entirely
by the rewards and punishments that its receives from the environment,
and not by any genetic influences. To caricature this radical
behaviourist position, its detractors would joke that one behaviourist
who met another in the street would have no choice of greeting
except “You’re fine today. How am I?”
During this same period when the behaviourists
were active—the mid-20th century—the series of conferences
mentioned at the start of this section gave rise to a new school
of thought known as cybernetics (follow the
Tool module link to the left). Cybernetics
looks at the way that information circulates both in living
organisms and in complex artificial systems designed by human
beings. Hence it is no surprise that computer science, in its
infancy at the time, drew much inspiration from cybernetics.
At the same time, linguistics was also developing
into a genuine scientific discipline, dedicated to one of the most
sophisticated human mental abilities: language.
In the 1960s, critiques of behaviourism by linguists such as Noam
Chomsky revealed its shortcomings when it came to studying complex
phenomena such as human language. These attacks dealt just as harsh
a blow to behaviourism as the writings of Watson had to structuralism
earlier in the century.
In short, as all of these new disciplines
(cybernetics, computer science, linguistics, etc.) evolved, the
human mind came to be treated less and less as a black box, and
the disciplines themselves began to interact in creative ways
that some called the cognitive
The philosopher Daniel
Dennett compares the classical model of consciousness
to a stage in a theatre. The part of the stage that is in
the spotlight would represent that which is conscious. This
model therefore implies the presence of a spectator who can
tell what part of the stage is lit—in other words,
what the content of consciousness is at any given time.
Dennett and other philosophers argue that the need for such
a “homunculus” (little man) in order to make consciousness
possible immediately results in what they call infinite
regress. Because who is going to enable this spectator
to become conscious of the part of the stage that is lit, if
not another spectator sitting inside his head, and so on to
One important part of
the scientific method is to formulate an initial hypothesis,
then attempt to invalidate it by conducting appropriately
designed experiments. To attempt to invalidate the Cartesian-theatre
model of consciousness, scientists would therefore try to conduct
experiments demonstrating that consciousness is not an all-or-nothing
event but can rather take intermediate forms and hence is a variable.
How might they do so? First of all, by trying to find at least
one other possible state of consciousness, because the defining
characteristic of a variable is that it can vary! And indeed,
this is why there have been so many neuroscientific experiments
designed to detect mental processes that are unconscious
or partially conscious.
An example of the application of this approach in another
discipline would be the discovery of near-zero gravity in space
compared with terrestrial gravity. Indeed, it was by imagining
gravity with different magnitudes and directions that Newton
was able to solve the age-old problem of the movement of the
Discovering conditions for comparisons has even unlocked the
door to entire scientific disciplines such as biology (species
are not fixed, but vary
over geologic time), earth science (the positions
of the continents are not stable but instead drift), etc. And
just like the study of consciousness, all of these breakthroughs
encountered staunch opposition in their own time.
In this popular view, consciousness is seen as a
container for ideas and images, with a window onto the world for
purposes both of perceiving it and of taking action in it. Some
call this the “naïve realist” model of consciousness;
it is the model that appeals to our common sense, the model that
we typically have by default.
The Classical Model of Consciousness
Dennett takes vigorous exception to this model (see sidebar).
He nicknames it the “Cartesian theatre”, because it
assumes that we examine ideas “in the light of reason”,
which illuminates them like a spotlight illuminates a theatre stage
or a projector illuminates a movie screen.
Infinite regress generated by
the use of a homunculus
in the Cartesian theatre model of
consciousness (see sidebar).
After Jennifer Garcia
of this theatrical model of consciousness actually date back
before Descartes all
the way to Plato. It is one of the most tenacious metaphors
for human consciousness. This is no surprise, because it
fits so intuitively with so many ways that we conceptualize
our own thought processes—for example, when you say “I
see” (in the theatre of your mind) to mean “I
understand”, or when you talk about getting an idea
in your head.
A list of the characteristics of this
model of consciousness would look something like this:
perception is a transparent window on
our actions are caused by our intentions,
which are freely generated by our consciousness;
these intentions form in our consciousness
on the basis of assumptions to which we have conscious access;
this implies that there is a place in
the brain where information is collected in order to be rendered
conscious—a place where consciousness springs into being
in an all-or-nothing fashion;
the mechanisms of perception and action
are completely transparent and can be accessed for scrutiny
by our consciousness on demand;
unconscious cognition is not recognized
in this model.
In the history of science, many important
breakthroughs have come when something that was previously assumed
to be a constant (for example, gravity, or atmospheric pressure)
was ultimately proved to be a variable (see sidebar). The classical
model presents consciousness as a unitary, indivisible, “all
or nothing” phenomenon—in short, a constant. But
is it really?
This is why so many neurobiologists are
trying to demonstrate the existence of unconscious mental processes
in perception, thought, and action, and they are succeeding in
doing so. Because the classical model of consciousness leaves
no room for unconscious processes, every successful scientific
demonstration of their existence demonstrates a flaw in this
model. And these
flaws are so numerous that this model is on the verge of
“Man no longer has
a need for the ’Spirit’; it is enough for him to
be Neuronal Man.”
- Jean-Pierre Changeux, Neuronal Man: The Biology of
Mind (1983, tr. 1997).
“And to those who might object that observing a brain
will never let us see consciousness, intelligence, or love,
Jean-Pierre Changeux retorts that it’s the same thing
when you open an alarm clock: you’re never going to see
what time it is.”
- Daniel Baril, Forum (November 18, 2002).
The central idea of eliminative
materialism is that old theories
can be eliminated by new, more relevant ones to account
for the progress of science.
The history of science is full of problems that were once
considered unsolvable and for which a better explanation was
later found. For example, heat was long regarded
as one of those phenomena that would never be explained, until
scientists came to understand what molecules were, and how
molecules that move more rapidly cause higher temperatures.
The same thing happened with chromosomes.
At the start of the 20th century, no one could imagine how
these large molecules, which all seemed to look alike, could
possibly contain the maps for the entire organism in all its
complexity. It was not until the structure
of DNA was discovered by James Watson and Francis
Crick in the early 1950s that scientists could crack
the genetic code and clarify what had been regarded as a mystery
scarcely 50 years earlier.
Eliminative materialists believe that just as a clearer understanding
of the mechanisms of life itself was thus derived from a better
understanding of the details of molecular mechanics and of
and transcription of DNA and its translation into protein,
so neurobiological models of consciousness will become clearer
as scientists gradually develop a better understanding of the
details relevant to this problem.
To continue with this analogy that is often drawn between
the explanation of life and the explanation of consciousness,
if life comes down to chemistry, then consciousness comes down
to a form of neuronal activity in the brain, and our mental
objects are therefore neuronal objects. Needless to say, eliminative
materialists harshly criticize functionalists,
who believe that a knowledge of the human brain is of no use
for understanding human cognition.
imaging techniques that were developed in the 1970s
and 1980s and that have become widely accessible since the
1990s enable scientists to visualize the variations in the
brain’s activity while it is performing different tasks.
By providing this capability, these techniques are what has
really enabled the neurosciences to become part of the cognitive
Researchers in the cognitive neurosciences
(see box to the right) have attempted to draw connections between
mental states (which are perceived, felt, and hence subjective)
and neural states (which are physical states of the brain and
hence observable and measurable).
These research programs are thus attempting
to identify the “neural correlates of consciousness”—
the processes that occur in the brain’s circuits during
a particular conscious experience. The cognitive neurosciences
thus operate from a clearly materialist perspective and hence are the target of criticism by other
But the fact is that a scant few decades
ago, the neurosciences were just one branch of the cognitive
sciences, which in turn were focused largely on the goals of
research into artificial
intelligence. Now the neurosciences are at the very
centre of the cognitive sciences.
SOME PROMISING CONCEPTS AND MODELS FROM THE NEUROSCIENCES
we approach the end of the first decade of the 21st century,
the number of books, conferences, and special issues of journals
devoted to the relationships between the brain and consciousness
has become simply overwhelming. It was not always thus. In
the 1980s, the scientific community still considered it premature
to be formulating any hypotheses about the mechanisms of consciousness.
But the 1990s saw an explosion of scientific
enthusiasm for such initiatives, in large part because of research
in the neurosciences and
the accessibility of increasingly high-performance devices for
imaging the brain (follow the Tool Module link to the left).
As a result, attitudes about studying the neurobiological bases
of consciousness have changed
dramatically. As the American philosopher John Searle put it
when describing the value of the Journal of Consciousness
Studies: “We don’t know how it works and we
need to try all kinds of different ideas.”
This ferment of new ideas has given
rise to many neurobiological
theories of consciousness that often have some key
concepts in common. The figure below attempts to illustrate
these commonalities. At the centre of the circle are the names
of some important authors of such theories, while around the
outside are some key concepts that are shared (with minor variations)
by the two authors or sets of authors whose names appear adjacent
Many people see this conceptual convergence
as a sign that a “mature” theory of consciousness
is starting to emerge. One thing is certain: concepts from the
neurosciences are now enabling us to go beyond the classical
model of consciousness and avoid its
flaws and shortcomings. Even so, the subjective essence of “what
it means” to be conscious remains an issue that is
very difficult to address scientifically.
Some scientists ascribe genuine importance
to this subjective aspect of consciousness, but add that if consciousness
is to be investigated effectively, better methods of interpreting
the relevant subjective data will have to be found.
Other scientists attempt to minimize
the importance of the subjective nature of human consciousness. Francis
Crick, for example, believes that only once we have
managed to understand the neurobiological mechanisms of consciousness
will we be in a position to understand its subjective qualia,
and that until then we therefore should not accord them too much
importance. This is a common strategy in science: concentrate
on the things that are more amenable to experimentation, while
hoping that those which are less so will subsequently become
clearer in light of the experimental results obtained.
One of the forerunners of this neurobiological
approach to the study of consciousness was the French neurobiologist Jean-Pierre
Changeux, who defended a neuronal theory of thought
in his book L’Homme neuronal, first published
in 1983 and now available in English under the title Neuronal
Man: The Biology of Mind.
Changeux clearly posits a causal relationship
between the structure of the brain and the function of thought.
From this relationship, it follows that consciousness is the
result of interactions among neurons in which the nerve
impulse takes a path that could ideally be described objectively.
And this path, it must be remembered, is not fixed, but instead alters
itself with use, thus constantly modifying our representations
of the world.
The similarities that the main neurobiological
theories of consciousness share with regard to certain concepts
are also seen in the neuronal circuits and brain
structures that these theories identify as playing a key
role in conscious thought. Obviously, not all parts of the brain
participate equally in conscious processes. There are, for example, numerous
unconscious processes that take place beneath the cortex
and have no conscious counterpart.
It is therefore important to stress
that the cognitive
neurosciences do not attempt to analyze the functioning of
these structures in isolation, but rather to understand the orderly
functioning of the brain as a whole, at the most integrated level
possible—that is, at the level where ion
channels, receptors, synapses, neurons,
assemblies all come into play collectively and simultaneously.
When philosophers impatiently
point out that the models of consciousness proposed by the neurobiologists
are still unclear, the neurobiologists freely admit that they
are only in the early stages of a long struggle to penetrate
the mysteries of consciousness. They
also point out that in scientific research, investigators must
begin by looking for correlations between observations before
they start inferring any causal mechanisms (see sidebar). When
this search for the “neural correlates of consciousness” is
thus viewed as part of a long-term effort, many of the criticisms
levelled at it become irrelevant.
Koch is a good example of a neurobiologist who
applies this gradualist approach, conducting experiments
on the most elementary forms of attention.
He hopes that once we understand them, the problems that
now seem unsolvable will become much simpler. Like many other neurobiologists,
Koch acknowledges that we may have to discover some new laws
governing the physical world before we can explain consciousness,
and that it may even remain a mystery forever. But the scientists
of the future will have to make that judgment, which he says
they can do only after all empirical avenues of inquiry have
been exhausted (if such a thing is possible).
And it is not only neurobiologists
who take exception to the view of David Chalmers that
consciousness is such a hard
problem that it is beyond the reach of neuroscience to solve.
Some philosophers too, of whom the most representative are probably Paul and Patricia
Churchland, find it counterproductive to treat human
consciousness as a special case, distinct from all the other
problems involved in understanding the human mind.
For the Churchlands, and for other
philosophers and researchers who are identified as eliminative
materialists, all questions about consciousness can be reduced
to what Chalmers calls the “easy problems” and eventually
be solved. Simply put, the concepts of popular psychology that
we use to explain our mental states (intentions, beliefs, desires,
etc.) are only approximations that will eventually be replaced
models that have yet to be developed.
And according to Patricia Churchland,
the fact that it is currently very hard for us to imagine a solution
to the problem of consciousness tells us absolutely nothing about
whether or not this phenomenon can actually be explained. In
her view, it is too easy to conclude that a phenomenon such as
consciousness is inexplicable simply because current human psychology
cannot grasp it.
people believe that since the last decade of the 20th century,
a second “cognitive
revolution” has been under way: the revolution
of the cognitive neurosciences.
To really understand what is meant
by the cognitive neurosciences, one must recall that until
the late 1960s, the various fields of brain research were
still tightly compartmentalized. Brain scientists specialized
in fields such as neuroanatomy, neurohistology, neuroembryology,
or neurochemistry. Nobody was yet working with the full range
of investigative methods available, but eventually, the very
complexity of the subject at hand made that a necessity.
It was thus that the term“neurosciences” was
introduced in the United States in the late 1960s to reflect
this desire to apply a multidisciplinary approach to explore
the “continent of the brain”. Today, the neurosciences include
disciplines such as neurophysiology (the functioning of the
neurons), neuroanatomy (the anatomical structure of the nervous
system), neurology (the clinical effects of pathologies of
the nervous system), neuropsychology (the clinical effects
of pathologies of the nervous system on cognition and emotions),
and neuroendocrinology (the relations between the nervous
system and the hormonal system), and research centres tend
to house several such disciplines under the same roof in
order to encourage ongoing exchanges and joint publications.
The term cognitive neurosciences simply
refers to those neurosciences that more specifically investigate
the higher cognitive functions (such as language and