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L'émergence de la conscience

The Sense of Self

Help Lien : Aux frontières de la conscience Lien : Conscience Lien : Definitions of consciousness
Lien : Concepts of consciousness

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, consciousness
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 a proliferation of explanatory theories very few of which are likely to stand the test of time in their current form.

Will 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.

Lien : Von Economo Neurons, Intuition, and Phylogeny Lien : Brain cells and arrangements unique to human cerebral cortex Lien : Spindle Neurons and Frontotemporal Dementia Lien : DENDRITIC ARCHITECTURE OF THE VON ECONOMO NEURONS


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 deep sleep.

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”:

- not being asleep or not “losing awareness”;

- the state that can be altered by taking psychotropic drugs or by mental illnesses such as depression and generalized anxiety disorder;

- being aware of a particular external stimulus, such as an obstacle that you come up against, or of a mental state such as a memory or an emotion;

- consciousness of yourself as an autobiographical (or episodic) construct, so that you feel that you are the same person today as you were yesterday;

- your ability to examine your own behaviours and thereby determine your intentions and motivations;

- the moral judgments that you make about these behaviours and that give you the impression of having free will;

- that small inner voice that is always present yet is so tiny in proportion to all the unconscious processes going on in your brain.

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 consciousness. It 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.

Scientific knowledge about consciousness in these various senses is also very uneven. For example, scientists know a great deal about several brain structures that control consciousness in the sense of wakefulness. But when it comes to understanding consciousness in the sense of a particular subjective experience, there are still some tremendous problems to be solved.


Original modules
History Module: When the History of Science Sheds Light on the Philosophy of Mind When the History of Science Sheds Light on the Philosophy of Mind

Christof Koch, a Romantic Reductionist

The following joke summarizes the position of an idealist on the relationship between mind and matter:

“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 tell?

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.


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 mysterianism.

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 two realities.

René Descartes believed that the exchanges between the material body and the immaterial soul took place through the pineal gland. Descartes had noticed that this brain structure appeared to be the only one that did not come in a bilateral pair, but instead was single and centrally positioned. With our modern scientific knowledge of the importance of the pineal gland for the human biological clock, what Descartes proposed may seem somewhat far-fetched, but at the time he lived, it was an honest solution to a crucial question that remains the Achilles heel of dualist philosophies to this day.

Materialism, already 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 B.C.E.)

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 our working memory or visualize 7-dimensional space: the cognitive limits of the tool with which we think.

Each of the preceding four positions has been the target of criticism, and in response their champions have refined each of them, giving rise to numerous variants, especially in the case of dualism and materialism.


Lien : Béhaviorisme Lien : Behaviorism Defined Lien : FROM BEHAVIOURISM TO COGNITIVISM Lien : A Review of B. F. Skinner's Verbal Behavior
Lien : An Examination of Behaviorism: The Psychology of Applied Learning
Chercheur : Wilhelm Wundt
Original modules
Tool Module: Cybernetics Cybernetics

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.

Lien : Edward Bradford Titchener Lien : William James

Behaviourist psychologists 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.


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 the centuries.

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 of interest.

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 revolution.


Lien : Neurevolution Lien : La cartographie du système cérébral Lien : Daniel Andler (ENS),  Les neurosciences cognitives sont-elles réductrices? Lien : Jean Petitot (CREA),  Modélisation des architectures fonctionnelles
Original modules
Tool Module: Brain Imaging Brain Imaging
Experiment Module: A Protocol for Functional Brain Mapping by Functional Magnetic Resonance Imaging and Positron Emission Tomography   A Protocol for Functional Brain Mapping by Functional Magnetic Resonance Imaging and Positron Emission Tomography

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 infinity?

But the brain is not known to contain any one control centre analogous to this homunculus. The neurosciences indicate that instead, there are countless interconnected neuronal assemblies, and that most of their activity remains unconscious. In this sense, the theories of consciousness that ultimately develop from the neurosciences are very likely to mark just as great a departure from the classical model of consciousness as Einstein’s theory of relativity did from Newtonian physics.

Lien : Infinite regress Lien : Recours à des homoncules (Homunculus)

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 stars.

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.


As noted above, people use the word “consciousness” to mean many different things. But one image that it brings to mind for many of us is that little “me” sitting comfortably inside our heads, watching what’s going on in the world as if it were a movie. From time to time, your inner me may even comment on this movie, in the “small inner voice” that we all know so well, or appear to freely decide on a course of action or behaviour on the basis of what it sees in this movie.

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


Philosopher Daniel 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
The origins 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 the world;

  • 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.


As neuroscientists acquired more and more data about the workings of the brain, this model came in for more and more criticism, in particular because it makes so little allowance for all of the behaviours that we carry out unconsciously. Nowadays, in fact, the counter-reaction has reached the point that journals on consciousness are filled with reports on experiments demonstrating the presence of unconscious processes in the brain . But why so much insistence on the search for unconscious processes?

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?

With the classical model of consciousness, as with any other model, the scientific method is to try to invalidate it, to see, for example, whether it can be proven incorrect in certain respects, such as whether unconscious processes exist, or whether a mental representation can become conscious gradually, rather than all at once.

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 collapsing.


Lien : Matière et conscience Lien : L’homme neuronal Lien : The Hornswoggle Problem Lien : How a neural correlate can function as an explanation of consciousness
Lien : L’émergence de la conscience Lien : Of Chemistry and Consciousness Lien : Conscience, Mémoire et Attention Lien : Publications 1 - 20 of 153 in Neuroscience: Consciousness
Lien : Can neuroscience explain consciousness? Lien : Studies in Neurophilosophy Lien : Books of Patricia Churchland Lien : How to study consciousness scientifically
Lien : Neurophilosophy Lien : L’homme neuronal en perspective Lien : Facing Backwards on the Problem of Consciousness Lien : Book Review : Brain-Wise: Studies in Neurophilosophy by Patricia Smith Churchland
Lien : Book : Neural Correlates of Consciousness
Chercheur : Ilya Farber
Original modules
Tool Module: Brain Imaging Brain Imaging

A Monthly Podcast On Cognitive Science

Christof Koch, a Romantic Reductionist

“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).

Lien : Jean-Pierre Changeux dissèque «l’homme neuronal» aux Belles Soirées

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 the replication 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.

Histoire : Quand l'histoire des sciences éclaire la philosophie de l'esprit

The brain 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 sciences.

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 philosophical schools.

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.

Outil : L'imagerie cérébrale Expérience : protocole de cartographie fonctionnelle du cerveau avec IRMf et TEP

As 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 to them.

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, and neuronal 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.

Christof 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 by neurobiological 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.

Many 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 consciousness).

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