Final Report Summary - NEUROCONSC (Converging Criteria for Consciousness: Using neuroimaging methods to characterize subliminal and conscious processing)
Understanding the neuronal architectures that give rise to conscious experience is one of the central unsolved problems in neuroscience. The NeuroConsc project aimed at clarifying the brain architecture underlying conscious processing in adults, infants, patients and non-human primates. In the course of this project, we identified several reliable “signatures” of consciousness, i.e. brain responses that reliably indicate whether or not a person is conscious of a certain piece of information.
One such signature is a late, slow and global potential called the “P3b” wave, which indicates the presence of distribution activation in a global cerebral “workspace”. We have validated a simple auditory paradigm capable of eliciting this specific marker, and we have discovered that (1) in normal human adults, in several different paradigms, this signature reliably marks conscious perception, as opposed to the mere non-conscious processing of subliminal stimuli; (2) this late brain response vanishes during anesthesia or during sleep; (3) the presence of this marker of consciousness can be detected in infants as early as two months of age; (4) it is also detectable in awake non-human primates and vanishes when the animal is anesthetized (5) In brain-lesioned patients, this marker, when present, very likely indicates that the patient is still conscious (as opposed to being in an unconscious vegetative state).
In addition to this established marker, we have identified and characterized several novel signatures of consciousness, including (1) the “meta-stability” of brain responses over a period of a few hundreds of milliseconds; (2) the presence of intense, long-distance exchanges of information across the cortex; (3) the presence of dynamic fluctuations in such exchanges, deviating from the fixed functional connectivity imposed by the anatomy of cortico-cortical connections.
We also explored the depths of non-conscious processing. Several of our results pushed the limits of subliminal processing by demonstrating (1) non-conscious processing of the syntactic category to which a word belong; (2) subliminal combination of multiple non-conscious words into a meaningful phrase; (3) non-conscious detection of a letter target while being distracted by another cognitive task; (4) subliminal meta-cognition, i.e. unconscious knowledge that we made an error; (5) subliminal working memory, i.e. a durable trace of non-conscious information for several seconds.
Finally, our research is leading to clinical applications. We collected what is probably the world’s largest collection of high-density EEGs from patients with disorders of consciousness (coma, vegetative state, minimally consciousness) and we used this database to demonstrate that our markers, together with other classical markers such as alpha or delta waves, provide an excellent diagnosis of the state of consciousness. Our pilot results suggest that they may detect residual consciousness in otherwise unresponsive patients, and may also have prognosis value in predicting which patients will or will not regain consciousness.
One such signature is a late, slow and global potential called the “P3b” wave, which indicates the presence of distribution activation in a global cerebral “workspace”. We have validated a simple auditory paradigm capable of eliciting this specific marker, and we have discovered that (1) in normal human adults, in several different paradigms, this signature reliably marks conscious perception, as opposed to the mere non-conscious processing of subliminal stimuli; (2) this late brain response vanishes during anesthesia or during sleep; (3) the presence of this marker of consciousness can be detected in infants as early as two months of age; (4) it is also detectable in awake non-human primates and vanishes when the animal is anesthetized (5) In brain-lesioned patients, this marker, when present, very likely indicates that the patient is still conscious (as opposed to being in an unconscious vegetative state).
In addition to this established marker, we have identified and characterized several novel signatures of consciousness, including (1) the “meta-stability” of brain responses over a period of a few hundreds of milliseconds; (2) the presence of intense, long-distance exchanges of information across the cortex; (3) the presence of dynamic fluctuations in such exchanges, deviating from the fixed functional connectivity imposed by the anatomy of cortico-cortical connections.
We also explored the depths of non-conscious processing. Several of our results pushed the limits of subliminal processing by demonstrating (1) non-conscious processing of the syntactic category to which a word belong; (2) subliminal combination of multiple non-conscious words into a meaningful phrase; (3) non-conscious detection of a letter target while being distracted by another cognitive task; (4) subliminal meta-cognition, i.e. unconscious knowledge that we made an error; (5) subliminal working memory, i.e. a durable trace of non-conscious information for several seconds.
Finally, our research is leading to clinical applications. We collected what is probably the world’s largest collection of high-density EEGs from patients with disorders of consciousness (coma, vegetative state, minimally consciousness) and we used this database to demonstrate that our markers, together with other classical markers such as alpha or delta waves, provide an excellent diagnosis of the state of consciousness. Our pilot results suggest that they may detect residual consciousness in otherwise unresponsive patients, and may also have prognosis value in predicting which patients will or will not regain consciousness.