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A SIGNATURE pattern of brain activity has been found that could help determine whether brain-damaged patients are conscious.
A team led by Aaron Schurger of Princeton University reasoned that repeatedly presenting the brain with the same sensory input should evoke similar neural activity each time 鈥� if the input is processed consciously. If it does not enter consciousness, activity should vary because other subconscious processes will be running at the same time.
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To see if this could be used to disentangle conscious from unconscious brain processes, the researchers asked 12 volunteers to look at images of faces and houses. The volunteers were shown either normal images, or versions of the same images presented as 鈥渋nvisible stimuli鈥�, to evoke unconscious processing.
The invisible images are formed by two drawings, one shown to each eye. In each pair, one drawing is in orange on a green background, while in the other the colours are reversed. Confronted with such contradictory inputs, the brain reconciles them by creating a yellow patch. So while the brain has subconsciously processed the face or house, the volunteer consciously sees nothing but yellow.
A set of functional magnetic resonance imaging recordings of the temporal lobes during both tasks backed up the researchers鈥� hypothesis: brain activity was similar each time a volunteer consciously looked at the same face or house, but invisible stimuli evoked a more variable response (Science, ).