"NOWHERE in science have so many devoted so much to create so little consensus," writes physicist, author and TV presenter Michio Kaku of consciousness research. So why, then, do we have yet another brace of books on the topic, one from cognitive psychologist Stanislas Dehaene and one from Kaku himself?
In Dehaene's case, the encouraging answer is that he sees progress in understanding consciousness coming out of his lab at the Cognitive Neuroimaging Unit in Saclay, near Paris – France's most advanced brain-imaging centre. Consciousness and the Brain is his excellent catch-up on the latest research, but there is a caveat: read a chapter at a time because it is jam-packed with intuition-altering experiments. In between, enjoy Kaku's madcap tour of the world's top brain labs, served up with whimsical insights in The Future of the Mind.
Dehaene expresses his own view of consciousness simply: "Consciousness is brain-wide information sharing." His book tells the story of why he thinks that and what it might mean. He begins his travels on a path pioneered by two luminaries, Francis Crick – on his second, post-DNA career – and Christof Koch. They were searching for unique "neural correlates of consciousness"; that is, the things that happen in particular parts of the brain only when you are consciously aware of something.
Dehaene has been making progress by presenting volunteers with visual stimuli cleverly designed so that they teeter on the threshold of conscious awareness. We learn that an effective method is to flash a stimulus image very quickly, sandwiched in time between a pair of different, "masking" images. If the duration of the stimulus – a word, for example – is carefully adjusted, then sometimes the word will get through to conscious awareness, and the volunteer can shout it out. Sometimes the volunteer will perceive nothing more than a flickering pattern. While conscious awareness shifts between on and off, scanners look for changes inside the brain and EEG machines pick up electrical signals from its surface. These data map out differences in the brain between the two states.
As his results mount up Dehaene gets excited, because he sees an "avalanche in the brain". When the threshold for conscious awareness is crossed, electrical activity in the higher visual centres is suddenly amplified and it spreads like a tsunami into regions of the parietal and prefrontal cortex – high-level areas of the brain which are never reached by the gentle waves of unconscious activity. Activation surges on into a much larger expanse of cortex, and distant brain regions start showing tightly correlated activity.
newscientist
