'Consciousness signature' discovered spanning the brain - health - 17 March 2009 - New Scientist

Description

Electrodes implanted in the brains of people with epilepsy might have resolved an ancient question about consciousness.

Signals from the electrodes seem to show that consciousness arises from the coordinated activity of the entire brain. The signals also take us closer to finding an objective "consciousness signature" that could be used to probe the process in animals and people with brain damage without inserting electrodes.

Previously it wasn't clear whether a dedicated brain area, or "seat of consciousness", was responsible for guiding our subjective view of the world, or whether consciousness was the result of concerted activity across the whole brain.

Probing the process has been a challenge, as non-invasive techniques such as magnetic resonance imaging and EEG give either spatial or temporal information but not both. The best way to get both simultaneously is to implant electrodes deep inside the skull, but it is difficult to justify this in healthy people for ethical reasons.

Brainy opportunity

Now neuroscientist Raphaël Gaillard of INSERM in Gif sur Yvette, France, and colleagues have taken advantage of a unique opportunity. They have probed consciousness in 10 people who had intercranial electrodes implanted for treating drug-resistant epilepsy.

While monitoring signals from these electrodes, Gaillard's team flashed words in front of the volunteers for just 29 milliseconds. The words were either threatening (kill, anger) or emotionally neutral (cousin, see).

The words were preceded and followed by visual "masks", which block the words from being consciously processed, or the masks following the words weren't used, meaning the words could be consciously processed. The volunteers had to press a button to indicate the nature of the word, allowing the researchers to confirm whether the volunteer was conscious of it or not.

Between the 10 volunteers, the researchers received information from a total of 176 electrodes, which ...

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