The leading theory of consciousness has been overturned and questioned. Ten years’ worth of research suggested the theory that brain signals vary depending on conscious or unconscious activity. However recent research has shown brain signals thought to reflect consciousness are also generated during unconscious activity.
The initial theory was that when a something is perceived unconsciously it is processed locally in the brain. Whereas when something is conscious it is processed in various brain region leading to activity over the entire network.
Stanisislas Dehaene and his team from the National Institute of Health in France achieved results which called this theory into question. When analysing the brain activity of volunteers they found that when viewing stimuli which are either conscious or unconscious an identical EEG is produced for the first 270 milliseconds. The activity measured is of the EEG signal of P3b often referred to as the ‘neural correlate’ of consciousness. After this period if the stimuli is subliminal the activity of the brain will decline whereas if it is conscious there will be a widespread increase of brain activity.
Other research was conducted by Brian Silverstein and Michael Snodgrass at the University of Michigan who were interested in detecting if P3b could be detected during unconscious stimuli processing.
They used the ‘oddball paradigm’ in which one stimulus is presented frequently , in this case the word ‘left’ which was shown for 7 milliseconds, interspersed with an ‘oddball ‘ stimulus, here the word ‘right’.
During the rare stimulus a strong P3b signal could be detected widely across the brain; even though the volunteers did not know what the stimuli was they could recognize something was unexpected. This provided evidence that P3b is not a ‘neural correlate’ of consciousness and so contradicts the initial global neuronal workspace theory.
This work is therefore extremely exciting as Anil Seth of the University of Sussex said: “It is pushing us towards more refined explanations that actually connect neural dynamics to what it is like to be conscious.”