By MORGEN E. PECK - SCIENTIFIC AMERICAN
Added: Mon, 05 Dec 2011 21:26:14 UTC

Brain areas send signals back and forth to generate conscious thoughts
Scientists have long hunted for a pattern of brain activity that signals consciousness, but a reliable marker has proved elusive. For many years theorists have argued that the answer lies in the prefrontal cortex, a region of high-level processing located behind the forehead; neural signals that reach this area were thought to emerge from unconscious obscurity into our awareness. Recent research, however, supports the idea that consciousness is a conversation rather than a revelation, with no single brain structure leading the dialogue.

The most recent to challenge the prevailing theory is Simon van Gaal, a neuroscientist who investigates the borders of conscious awareness at the Neurospin Institute in Paris. He asks participants in his ongoing experiments to push a button every time they see a symbol flash on a screen, except when they see a certain icon that means “stop.” During some of the trials van Gaal flashes the stop signal in a way that the subjects cannot consciously perceive. Although they do not see the stop signal, they hesitate to push the button, as though some part of the brain were choking on the information. As he runs the test, van Gaal measures brain activity with functional MRI and electroencephalo­graphy (EEG). He has found that the unconscious inhibitory signal seems to make it all the way up to parts of the prefrontal cortex.
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TAGGED: MEDICINE, PSYCHOLOGY