Cortical Neural Synchronization Underlies Primary Visual Consciousness of Qualia: Evidence from Event-Related Potentials

Behavioral assessment scale of consciousness for nonhuman primates: A Delphi study

OBJECTIVE

Nonhuman primates (NHPs) are suitable for being model animals in the study of consciousness and loss of consciousness (LoC) with a similar brain structure and function to humans. However, there is no effective consciousness assessment scale for them. This study aimed to develop a behavioral assessment scale of consciousness for NHPs.

METHODS

We constructed an initial indicator framework based on the clinical consciousness disorder assessment scales and the physiological characteristics, consciousness, and arousal behavior of NHPs. A two-round online Delphi method was conducted by a multidisciplinary expert panel to construct a behavioral assessment scale of consciousness for NHPs. The indicators and descriptions were revised according to the experts' feedback and then sent out for repeated consultations along with a summary of the results of the previous round of consultations. The accepted competencies of indicators were established with mean scores in two scoring criteria (importance and feasibility) ≥4.0, agreement rate with a rating of importance or essential ≥70.0%, and a coefficient of variation ≤0.25, as well as discussions of the research group.

RESULTS

Consensus was achieved after the second round of consultations, which was completed by 28 experts who specialized in rehabilitation, neuroscience, psychology, neurosurgery, and neurology. A new behavioral assessment scale of consciousness for NHPs, including 37 items organized hierarchically within seven dimensions including visual function, auditory function, motor function, orofacial movements, arousal, brainstem reflexes, and respiration, was developed in this study.

CONCLUSIONS

This study has successfully developed a behavioral assessment scale for measuring the conscious state of NHPs or NHP models with LoC. This tool is expected to facilitate future research into the underlying mechanisms of consciousness by providing a detailed and comprehensive means of measurement.

Perceptual awareness negativity: a physiological correlate of sensory consciousness

Much research on the neural correlates of consciousness (NCC) has focused on two evoked potentials, the P3b and the visual or auditory awareness negativity (VAN, AAN). Surveying a broad range of recent experimental evidence, we find that repeated failures to observe the P3b during conscious perception eliminate it as a putative NCC. Neither the VAN nor the AAN have been dissociated from consciousness; furthermore, a similar neural signal correlates with tactile consciousness. These awareness negativities can be maximal contralateral to the evoking stimulus, are likely generated in underlying sensory cortices, and point to the existence of a generalized perceptual awareness negativity (PAN) reflecting the onset of sensory consciousness.

ERP and MEG correlates of visual consciousness: The second decade

The first decade of event-related potential (ERP) research had established that the most consistent correlates of the onset of visual consciousness are the early visual awareness negativity (VAN), a posterior negative component in the N2 time range, and the late positivity (LP), an anterior positive component in the P3 time range. Two earlier extensive reviews ten years ago had concluded that VAN is the earliest and most reliable correlate of visual phenomenal consciousness, whereas LP probably reflects later processes associated with reflective/access consciousness. This article provides an update to those earlier reviews. ERP and MEG studies that have appeared since 2010 and directly compared ERPs between aware and unaware conditions are reviewed, and important new developments in the field are discussed. The result corroborates VAN as the earliest and most consistent signature of visual phenomenal consciousness, and casts further doubt on LP as an ERP correlate of phenomenal consciousness.

Information and the Origin of Qualia

This article argues that qualia are a likely outcome of the processing of information in local cortical networks. It uses an information-based approach and makes a distinction between information structures (the physical embodiment of information in the brain, primarily patterns of action potentials), and information messages (the meaning of those structures to the brain, and the basis of qualia). It develops formal relationships between these two kinds of information, showing how information structures can represent messages, and how information messages can be identified from structures. The article applies this perspective to basic processing in cortical networks or ensembles, showing how networks can transform between the two kinds of information. The article argues that an input pattern of firing is identified by a network as an information message, and that the output pattern of firing generated is a representation of that message. If a network is encouraged to develop an attractor state through attention or other re-entrant processes, then the message identified each time physical information is cycled through the network becomes “representation of the previous message”. Using an example of olfactory perception, it is shown how this piggy-backing of messages on top of previous messages could lead to olfactory qualia. The message identified on each pass of information could evolve from inner identity, to inner form, to inner likeness or image. The outcome is an olfactory quale. It is shown that the same outcome could result from information cycled through a hierarchy of networks in a resonant state. The argument for qualia generation is applied to other sensory modalities, showing how, through a process of brain-wide constraint satisfaction, a particular state of consciousness could develop at any given moment. Evidence for some of the key predictions of the theory is presented, using ECoG data and studies of gamma oscillations and attractors, together with an outline of what further evidence is needed to provide support for the theory.