Consciousness and the Brain: Deciphering How the Brain Codes Our Thoughts

As a physician and Stanford researcher (initially in artificial intelligence and currently in cognitive neuroscience), I have been interested in consciousness research for 50 years. How does the brain create consciousness? And, if this is "simply" a story of billions of spiking neurons talking to one another, can it be done in silicon? (If so, this may occasion a profound turning point in human history.)

I have followed Professor Stan Dehaene's prestigious journal publications for a decade as he has amassed a wealth of evidence supporting the view that consciousness is 1) experimentally accessible, 2) has reliable neural correlates (signatures), and 3) is functionally important . Dehaene (a professor at the College de France in Paris and director of the INSERM Cognitive Neuroimaging Unit) is one of the world's leading scholars of consciousness. Fortunately for us, his literary agent, John Brockman (of "Edge" fame) persuaded him to write this popular work.

That Dehaene writes this well in English makes me wonder how spectacularly he must write in his native French. We are not only transported to the cutting edge of research on consciousness, but the voyage is a thrill. As expected, Dehaene is thoroughly steeped in the history of consciousness from Plato, through Descartes, Hume, and the Continental philosophers. His writing is also filled with references to French art, literature, and humanism (like serotonin molecules, that culture seems to have diffused from the Louvre down the Boulevard Saint-Michel and become bound in this book.)

Right from the start (see the beautiful, free Introduction on Amazon) he reminds us that it all began in the caves at Lascaux with the depiction of a dreamer's soul wafting about like a sparrow. Deftly weaving ancient Egyptian mythology with the Upanishads, he transitions to Descartes and his alleged "Error." Rightfully defending his countryman, Dehaene takes contemporary pop-neurosci to task. Descartes was no dualist (body + immaterial soul) blinded by religion. Rather, he was genuinely grappling with the central problem of this book and the field. How does conscious perception, reflection, and deliberation emanate from a machine?

In seven chapters, Dehaene carefully steps us through all the evidence (from his large Paris group and the world's other top labs) of the brain's signatures of consciousness.

How can one even study consciousness in the lab? (Chapter 1) The key innovation was the discovery and exploitation of "minimal contrast" phenomena. When presented just too faintly, too rapidly. or when masked they are completely invisible. But, increase the intensity, duration, or remove the mask and there they are, plain as day. I'll list these, but do yourself a favor and go to YouTube to see them for yourself: motion-induced blindness, change blindness, attentional blink, binocular rivalry, multistable perception. Now you see it; now you don't. (Also, go to Charlie Rose's website and look at the episode on consciousness in which Nobelist Eric Kandel interviews Dehaene and other stars of this field.)

We are obviously conscious, but is there any neural processing of which we are NOT conscious?
(Chapter 2) Yes, most of it! Non-conscious and pre-conscious processing is ubiquitous, functional, and essential. He reviews fascinating experiments that reveal the pervasive and essential role of non-conscious processing in language, vision, hearing, and action. Consciousness is the tip of the iceberg.

Perhaps consciousness is epiphenomenal (a non-functional add-on, like the roar of a jet plane). In Chapter 3 he dismisses that old, profoundly counter-intuitive proposition. His argument here is reminiscent of Kahneman's Thinking Fast and Slow. Fast (nonconscious) thought is fine for practiced, routine, reflexive speech and action. But thinking and action marked by careful deliberation and planning requires consciousness: the ability to maintain a percept in working memory and mull it over.

Chapter 4 displays the core findings of the experimental work: the neural signatures of consciousness. These are what Nobelist Francis Crick and collaborator Christof Koch called the neural correlates of consciousness. (See Koch's excellent work "The Quest for Consciousness") Even invisible, unseen (subliminal) stimuli excite chains of neural firing but only in primary sensory areas. However, when a stimulus crosses the threshold into consciousness, the neural firing is strongly amplified in intensity and distribution as many brain regions ignite and communicate especially prefrontal, parietal, and anterior temporal areas.

In Chapter 5 he describes a tentative theory that accounts for the experimental findings: the global neuronal workspace theory. I'm old enough to recall the origin of this theory as the blackboard model from 1970s AI research sponsored by DARPA that led to the then famous Hearsay-II speech understanding system from CMU. In an interesting quirk of history, this excellent work was dragged into oblivion by the AI Winter of the 1980s. But, the theory itself became resurrected as a theory of consciousness by psychologist Bernard Baars. (See Baars' 1988 A Cognitive Theory of Consciousness). With the 1990 advent of fMRI, this theory became ripe for experimental verification. Entrez Professeur Dehaene. Not only can he explain the lab details from Chapter 4, he has also built a computer simulation of a spiking neural network that exhibits the same behavior.

As you may know, Europe has just embarked on a ten year 1.5 billion dollar project to simulate the human brain. While this project may seem to be irrationally ambitious, I am comforted in knowing that Dehaene is one of the scientists at the helm.

Chapter 6 deals with the crucial topic of coma and vegetative states. It opens poignantly with the case of Jean-Dominique Bauby, the Editor of Elle, who had a brain stem stroke, and though entirely paralyzed (save for one eye), wrote an entire book "The Diving Bell and The Butterfly" by blinking that eye. EEG, MEG, and fMRI signatures of consciousness may in the future help us to decide which coma patients are conscious and which are not.

He closes in Chapter 7 with the future: tests for animal consciousness and machine consciousness. While machine consciousness may someday be possible, it will not happen soon. Nonetheless, this work paves the way to it by showing the functional properties of the only system that we know is conscious: ourselves.

Although I've read widely on this topic (and cover AI and Stanford neuroscience on my website: bobblum) , there was much here that was new to me. This is an outstanding work on the basis of both scientific and literary merit.

I've read many books on consciousness but none that so satisfyingly summarizes the recent experimental research. Though his native language is French, Dehaene writes brilliant and lucid English--no wonder he cites Nabokov so often! The topic is a tough one for a nonprofessional like myself, but the author patiently takes us through the various ways consciousness can be detected and how, through various instruments, we can see the signs of its operation. There's an unusual warmth to the writing as well--Dehaene must be a remarkable individual. All in all, this is a splendid example of clear exposition. My only disappointment came at the very end where I thought Dehaene rushed his argument a bit and exaggerated the prospects of our being able to model human consciousness in machines. I thought he needed to consider David Chalmers' idea of "qualia" more carefully. I also wish he'd have paid just a little attention to Henri Bergson's too-easily dismissed theories and John Searle's more recent work on perception. But perhaps such matters will be covered in the next book, which I eagerly await.

An extremely interesting book for those interested in the field.
One Caveat, though. I've learned about the subject from various neuro-researchers: Michael Gazzaniga, Giulio Tononi, Susan Greenfield, Mark Solms, Zvi Rappaport, or Antonio Damasio. All of them are very knowledgeable, and I've learned a lot from all of them as well as from Stanislass Dehaene's book I'm reviewing here. The amazing thing is that even though many of them draw a clear picture, there is very little overlap.

This makes each of the sources even more interesting, but it also shows that the topic has not yet been matured. Dehaene's book concentrates on the pattern of information processes, and about what happens at the stage where some of the information (after being well digested by the brain) comes to our conscious awareness. The problem is that at this stage, there is so much activity, that it is very hard to pinpoint what is the result of things becoming to our conscious awareness, or what just accompanies it.

It is wonderful to find a book that has taken consciousness from a philosophical subject, approachable mostly by way of metaphor, to the scientific, experimental level.
Mr. Dehaene begins, as is often necessary in science, by defining the term consciousness in a clear and unambiguous manner that delineates it from other related and often conflated terms such as awareness and attention.
But the majority of this book concerns data taken from nuts-and-bolts experiments in the lab, many using brain-imaging equipment, that give information about actual brain processes that occur during consciousness and how they differ from those of unconscious processing. And sometimes startling insights about the evolution of consciousness and the reasons it may have developed.
Four "signatures" of consciousness were identified from this experimental data, and using these signatures, a theory of consciousness was developed and also a practical method for determining the actual state of animals, babies, or patients who have suffered brain trauma or paralysis and are not able to communicate directly with people.
This is cutting-edge, ground-floor science, and I am thankful to live in an era where I can access this knowledge. It is in the nature of science that new experiments and findings on the nature of consciousness will doubtless now occur rapidly, but this is the finest book on consciousness I have read thus far.