Tuesday, 28 October 2014

Consciousness and the Brain: Deciphering how the brain codes our thoughts (Viking, New York)

Stanislas Dehaene (2014): Consciousness and the Brain: Deciphering how the brain codes our thoughts (Viking, New York)

(also available through LibGen)

Dehaene is a leading neuroscientist on consciousness, and an extremely smart guy. His analysis of consciousness is based on massive amounts of experimental and observational evidence together with a coherent theory (the global neuronal workspace). He does away with all the vagueness, obscurity, wild speculation, and philosophical nonsense that is usually associated with the concept of consciousness. Instead, he focuses on the direct connections between measurable neural processes and subjective, conscious experiences, in order to tease out exactly what distinguishes conscious from subconscious cognitive processes, and how the former can emerge from the latter.

He moreover offers a clear and convincing explanation of why consciousness evolved as a control layer on top of earlier subconscious processing. His main idea is that subconscious processes proceed in parallel in a lot of specialized modules while constantly changing the state of activation of the brain. Consciousness selects the most important of these subconscious perceptions and conceptions and puts it in a temporary buffer, the "working memory" or "global workspace", where it can be examined, combined with other conceptions from different origins, and thus sequentially processed in a controlled manner. The contents of the global workspace are then broadcasted to all other brain regions, so that the focus of consciousness can direct the activity of otherwise independent, automatically proceeding subconscious modules.

The emergence of a conscious thought in the global workspace happens through a phase transition which Dehaene calls "ignition", in which a wide area of the cortex suddenly becomes activated and synchronized in its firing. It is is based on a positive feedback of activated neurons activating more neurons, until they form a coherent, self-sustaining pattern that corresponds to a particular thought. This pattern simultaneously suppresses the activation of all other neurons not related to the conscious thought. Thus, thoughts compete for access to the global workspace, according to a "winner takes all" dynamics that only allows a single thought to be in focus at a time.

That explains the sequential processing characterizing consciousness, but not yet the capacity of working memory, which can sustain roughly 4 items for eventual combination (e.g. when you make a mental calculation involving several numbers). (A possible explanation is that working memory is broader than global workspace, keeping items that are no longer in focus weakly activated so that they can easily reenter the workspace when needed). Perhaps Dehaene will explain this in the chapters I have not read yet...

If you read only one book or article on consciousness, this should be it. Forget about zombies, the "hard problem" and other philosophical thought experiments that have no relation to the real world. This is scientific research the way it should be done: based on concrete evidence, with lots of practical implications, yet grounded in deep, elegant and general theoretical modelling.

Moreover, Dehaene has the talent to write a book that goes into quite a bit of technical and theoretical detail, yet is easy and fun to read. Highly recommended!

Here's the book's blurb:

A breathtaking look at the new science that can track consciousness deep in the brain

How does our brain generate a conscious thought? And why does so much of our knowledge remain unconscious? Thanks to clever psychological and brain-imaging experiments, scientists are closer to cracking this mystery than ever before.

In this lively book, Stanislas Dehaene describes the pioneering work his lab and the labs of other cognitive neuroscientists worldwide have accomplished in defining, testing, and explaining the brain events behind a conscious state. We can now pin down the neurons that fire when a person reports becoming aware of a piece of information and understand the crucial role unconscious computations play in how we make decisions. The emerging theory enables a test of consciousness in animals, babies, and those with severe brain injuries.

A joyous exploration of the mind and its thrilling complexities, Consciousness and the Brain will excite anyone interested in cutting-edge science and technology and the vast philosophical, personal, and ethical implications of finally quantifying consciousness.

Francis Heylighen    
Evolution, Complexity and Cognition group
Free University of Brussels
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Image of Stanislas Dehaene

Stanislas Dehaene is a French psychologist and cognitive neuroscientist. He is currently heading the Cognitive Neuroimaging Unit within the NeuroSpin building of the Commissariat A l'Energie Atomique in Saclay near Paris, France's most advanced brain imaging center. He is also a professor at College de France in Paris, where he holds the newly created chair of Experimental Cognitive Psychology. In 2005, he was elected as the youngest member of the French Academy of Sciences.
Stanislas Dehaene's interests concern the brain mechanisms of specifically human cognitive functions such as language, calculation, and conscious reasoning. His research relies on a variety of experimental methods, including mental chronometry in normal subjects, cognitive analyses of brain-lesioned patients, and brain-imaging studies with positron emission tomography, functional magnetic resonance imaging, and high-density recordings of event-related potentials. Formal models of minimal neuronal networks are also devised and simulated in an attempt to throw some links between molecular, physiological, imaging, and behavioral data.
Stanislas Dehaene's main scientific contributions include the study of the organization of the cerebral system for number processing. Using converging evidence from PET, ERPs, fMRI, and brain lesions, Stanislas Dehaene demonstrated the central role played by a region of the intraparietal sulcus in understanding quantities and arithmetic (the "number sense"). He was also the first to demonstrate that subliminal presentations of words can yield detectable cortical activations in fMRI, and has used these data to support an original theory of conscious and nonconscious processing in the human brain. With neurologist Laurent Cohen, he studied the neural networks of reading and demonstrated the crucial role of the left occipito-temporal region in word recognition (the "visual word form area").
Stanislas Dehaene is the author of over 190 scientific publications in major international journals. He has received several international prizes including the McDonnell Centennial Fellowship, the Louis D prize of the French Academy of Sciences (with D. Lebihan), and the Heineken prize in Cognitive Science from the Royal Academy of the Netherlands. He has published an acclaimed book The number sense, which has been translated in eight languages, and is publishing a new book Reading in the brain, to appear in November 2009. He has also edited three books on brain imaging, consciousness, and brain evolution, and has authored two general-audience documentaries on the human brain   Bio from Amazon

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