Researchers have conducted studies and uncovered where exactly lies the origin of consciousness in the brain.
While some neuroscientists have argued that consciousness may arise from a single "seat" in the brain, the new study has suggested that four specific, separate processes combine as a "signature" of conscious activity.
For the study, researchers analyzed the neural activity of people who were presented with two different types of stimuli, one that could be perceived consciously, and the other that could not.
By using the above information, Dr. Gaillard of INSERM and colleagues showed that the four processes occurred only in the former, conscious perception task.
The new work addresses the neural correlates of consciousness at an unprecedented resolution, using intra-cerebral electrophysiological recordings of neural activity.
The researchers conducted all the challenging experiments on patients with epilepsy, who were already undergoing medical procedures requiring implantation of recording electrodes.
The authors presented them with visually masked and unmasked printed words, and then measured the changes in their brain activity and the level of awareness of seeing the words.
The method offers a unique opportunity to measure neural correlates of conscious access with optimal spatial and temporal resolutions.
When comparing neural activity elicited by masked and unmasked words, the researchers were able to isolate four converging and complementary electrophysiological markers characterizing conscious access 300 ms after word perception.
All the measures may provide distinct glimpses into the same distributed state of long-distance reverberation.
Thus, the researchers speculated that it is the convergence of these measures in a late time window (after 300 ms), rather than the mere presence of any single one of them, which best characterizes conscious trials.
"The present work suggests that, rather than hoping for a putative unique marker, the neural correlate of consciousness, a more mature view of conscious processing should consider that it relates to a brain-scale distributed pattern of coherent brain activation," explained neuroscientist Lionel Naccache, one of the authors of the paper.
Te study has been published in the latest issue of PLoS Biology.