ERP and MEG correlates of visual consciousness: The second decade.

To identify the neural correlates of perceptual awareness, researchers often compare the differences in neural activation between conditions in which an observer is or is not aware of a stimulus. While intuitive, this approach often contains a critical limitation: to link brain activity with perceptual awareness, observers traditionally report the contents of their perceptual experience. However, relying on observers' reports is problematic because it is difficult to know whether the neural responses being measured are associated with conscious perception or with postperceptual processes involved in the reporting task (e.g., working memory, decision-making). To address this issue, we combined a standard visual masking paradigm with a recently developed "no-report" paradigm in male/female human participants. In the visual masking paradigm, observers saw images of animals and objects that were visible or invisible, depending on their proximity to masks. Meanwhile, on half of the trials, observers reported the contents of their perceptual experience (i.e., report condition), while on the other half of trials they refrained from reporting about their experiences (i.e., no-report condition). We used electroencephalography to examine how visibility interacts with reporting by measuring the P3b event-related potential, one of the proposed canonical "signatures" of conscious processing. Overall, we found a robust P3b in the report condition, but no P3b whatsoever in the no-report condition. This finding suggests that the P3b itself is not a neural signature of conscious processing and highlights the importance of carefully distinguishing the neural correlates of perceptual awareness from postperceptual processing.SIGNIFICANCE STATEMENT What are the neural signatures that differentiate conscious and unconscious processing in the brain? Perhaps the most well established candidate signature is the P3b event-related potential, a late slow wave that appears when observers are aware of a stimulus, but disappears when a stimulus fails to reach awareness. Here, however, we found that the P3b does not track what observers are perceiving, but instead tracks what observers are reporting. When observers are aware of simple visual stimuli, the P3b is nowhere to be found unless observers are reporting the contents of their experience. These results challenge the well established notion of the P3b as a neural marker of awareness and highlight the need for new approaches to the neuroscience of consciousness.

https://www.jneurosci.org/content/jneuro/40/25/4925.full.pdf

Distinguishing the Neural Correlates of Perceptual Awareness and Postperceptual Processing.

Previous studies have shown that a single Coma-Recovery Scale-Revision (CRS-R) assessment can identify high rates of misdiagnosis by clinical consensus. The aim of this study was to investigate the proportion of misdiagnosis by clinical consensus compared to repeated behavior-scale assessments in patients with prolonged disorders of consciousness (DOC). Patients with prolonged DOC during hospitalization were screened by clinicians, and the clinicians formed a clinical-consensus diagnosis. Trained professionals used the CRS-R to evaluate the consciousness levels of the enrolled patients repeatedly (≥5 times) within a week. Based on the repeated evaluation results, the enrolled patients with prolonged DOC were divided into unresponsive wakefulness syndrome (UWS), minimally conscious state (MCS), and emergence from MCS (EMCS). Finally, the relationship between the results of the CRS-R and the clinical consensus were analyzed. In this study, 137 patients with a clinical-consensus diagnosis of prolonged DOC were enrolled. It was found that 24.7% of patients with clinical UWS were actually in MCS after a single CRS-R behavior evaluation, while the repeated CRS-R evaluation results showed that the proportion of misdiagnosis of MCS was 38.2%. A total of 16.7% of EMCS patients were misdiagnosed with clinical MCS, and 1.1% of EMCS patients were misdiagnosed with clinical UWS. The rate of the misdiagnosis by clinical consensus is still relatively high. Therefore, clinicians should be aware of the importance of the bedside CRS-R behavior assessment and should apply the CRS-R tool in daily procedures. ClinicalTrials.gov ID: 
NCT04139239

; Registered 24 October 2019 - Retrospectively registered.

/pdf/the-misdiagnosis-of-prolonged-disorders-of-consciousness-by-4qidy124ob.pdf

The misdiagnosis of prolonged disorders of consciousness by a clinical consensus compared with repeated coma-recovery scale-revised assessment.

Perceptual awareness negativity: a physiological correlate of sensory consciousness.

The role of levels of processing in disentangling the ERP signatures of conscious visual processing

Primary objective: The aim of this study was to determine the validity of the Polish version of the Coma Recovery Scale—Revised (CRS-R).Methods and design: Two trained raters, A and B, administered...

A validation of the Polish version of the Coma Recovery Scale-Revised : CRSR

The levels of perceptual processing and the neural correlates of increasing subjective visibility

The functional meaning and neural basis of the P3b component of ERPs are still under debate. One of the main issues is whether P3b reflects only stimulus-related processes (stimulus evaluation hypothesis) or response-related processes as well (stimulus-response or S-R link activation hypothesis). Here, we conducted an EEG experiment examining whether P3b may indeed reflect an S-R link activation, followed by an fMRI experiment in which we explored the brain areas and functional connectivity possibly constituting the neural basis of these sensorimotor links. In both experiments, two successive visual stimuli, S1 and S2, were presented with a 1 sec interval, and responses were defined either by S1 or S2, while participants responded only after S2 onset. The obtained EEG results suggest that P3b may be interpreted in terms of the S-R link activation account, although further studies are needed to disentangle P3-related activity from overlapping anticipatory activity. The obtained fMRI results showed that processing of the relevant S1 involved activation of a distributed postero-anterior sensorimotor network, and increased strength of functional connectivity within this network. This network may underlie activation of the S-R links, thus possibly also the P3b component, forming a bridging step between sensory encoding and response execution.

Krzysztof Gociewicz

Papers

The role of levels of processing in disentangling the ERP signatures of conscious visual processing

A validation of the Polish version of the Coma Recovery Scale-Revised : CRSR

The levels of perceptual processing and the neural correlates of increasing subjective visibility

The response relevance of visual stimuli modulates the P3 component and the underlying sensorimotor network.

Zaburzenia świadomości z perspektywy neuroobrazowania