Introduction to States of Consciousness

EDITORIAL article Front. Psychol., 01 September 2011 | https://doi.org/10.3389/fpsyg.2011.00191

The Equations for Consciousness: A Reply to “Tracking the Travels,” a Review of <i>Journey of the Mind</i>

Loss of nonstationary connectivity in a subcortical fronto-temporoparietal network distinguishes patients with minimal conscious state and unresponsive wakefulness state, strongly supporting the mesocircuit hypothesis.

Reviews

Towards solving the hard problem of consciousness: The varieties of brain resonances and the conscious experiences that they support

Patients with disorders of consciousness (DoC) are often misdiagnosed as being in a lower state of consciousness than they are, which can impede their access to care. Cut points for each state of consciousness on the Coma Recovery Scale-Revised (CRS-R) could support researchers in stratifying patients, facilitate interpretation of results, and enhance comparability across studies. The primary purpose of this study was to empirically examine the alignment between the CRS-R rating scale categories and states of consciousness on the same Rasch-transformed equal-interval ruler. States of consciousness included the unresponsive wakefulness syndrome (UWS), minimally conscious state (MCS), and emerged from MCS (eMCS). Our secondary objective was to generate and assess the sensitivity and specificity of the cut points for each DoC diagnosis on the equal-interval ruler. We hypothesize that empirically derived cut point thresholds will reclassify some records to a higher-level state of consciousness and provide enhanced precision at clinically relevant transitions. We used the Rasch measurement model to co-calibrate the CRS-R and two DoC diagnostic variables on a 0- to 100-unit equal-interval scale. One DoC diagnostic variable used the Aspen consensus criteria aligned to the CRS-R rating scale categories (Aspen-Based). The second DoC diagnostic variable was based on an examination of the CRS-R rating scale category difficulty (Rasch-Derived). We used CRS-R data from 262 participants with DoC (1,442 CRS-R records). The Aspen-Based DoC diagnostic variable indicated participants were UWS &lt;41.57, 41.57 ≤ MCS &lt; 73.16, and eMCS ≥73.16 units. Six CRS-R rating scale categories were not consistent with their Aspen-Based alignment to DoC state. Therefore, we realigned four of these six CRS-R rating scale categories to indicate their respective higher state of consciousness when we created the Rasch-Derived DoC diagnostic variable. After reclassifying the CRS-R records, 19% of the 1,442 CRS-R records reflected a higher state of consciousness. The Rasch-Derived DoC diagnostic variable indicated participants were UWS &lt;34.40, 34.40 ≤ MCS &lt; 67.07, and eMCS ≥67.07 units. We conducted a sensitivity and specificity analysis on the UWS to MCS and MCS to eMCS cut points using the Aspen-Based DoC and Rasch-Derived DoC person measures. We improved the existing sensitivity and specificity analyses by recommending a UWS to MCS cut point of 34.40 units and an MCS to eMCS cut point of 67.07 units on the 0- to 100-unit scale. Identifying additional rating scale categories that reflect higher DoC diagnoses (e.g., MCS or eMCS) and lower cut points for MCS and eMCS could have implications for improving the diagnostic accuracy of the CRS-R and ultimately, facilitating better access to medical and rehabilitation services. A future study should examine the external validation of the Rasch-Derived cut points using multimodal approaches such as neuroimaging or electrophysiologic evaluation.

Multiple Perspectives on Consciousness for Cognitive Science Richard A. Carlson (racarlson@psu.edu) Department of Psychology, Penn State University 613 Moore Building, University Park, PA 16802 USA The huge contemporary literature on consciousness spans multiple disciplines, including psychology, philosophy, and neuroscience. This tutorial will introduce participants to major proposals about consciousness, and their empirical and methodological implications. The goal is to prepare participants to explore the consciousness literature in greater depth. Our consideration of perspectives on consciousness will be organized by considering how these perspectives address core questions about consciousness, including: (a) How can subjectivity and agency be accommodated in a scientific theory of consciousness? (b) How can conscious and nonconscious or unconscious processes and representations be systematically distinguished? (c) How can conscious mental states be assessed or measured? (d) How can dissociations and impairments of consciousness be understood? The literatures to be considered address these questions in analytic, functional, computational, and implementational terms. Philosophical Perspectives Philosophers approach the problem of consciousness from a variety of analytic perspectives, some focusing on contemporary formulations of the mind-body problem and others on analyses of subjective experience. Among the philosophical perspectives we will consider are John Searle’s (1992) analysis of consciousness in terms of intentionality, David Chalmer’s (1996) distinction between “easy” and “hard” problems of consciousness, David Rosenthal’s (1993) “higher order thought” proposal, and Daniel Dennett’s (1991) “multiple drafts” theory of consciousness. Neuroscience Perspectives Neuroscientists have made a wide variety of proposals concerning the neural correlates of consciousness (NCC). A starting assumption is that a subset of current neural activity is correlated with current conscious experience. There is controversy, however, concerning how that subset is to be identified. For example, the NCC might be limited to particular types of cells or anatomical structures, or comprise global patterns of synchronized neural activity. We will consider recent proposals concerning NCC by Crick and Koch (1998), Damasio (2000), and Edelman and Tononi Psychological Perspectives Psychological perspectives on consciousness generally focus on functionally-defined aspects of cognition. For example, psychologists have identified consciousness with working memory (Baars, 1988), attention (Schneider & Pimm-Smith, 1997), metacognition (Nelson, 1996), and with the structure of mental states (Carlson, 1997). Cognitive research often focuses on distinguishing conscious and nonconscious influences on psychological processes such as learning (Dienes & Berry, 1997) and perception (Merikle, Smilek, & Eastwood, 2001). This research has generated a rich literature on methods for assessing consciousness. References Baars, B. J. (1988). A cognitive theory of consciousness. New York: Cambridge University Press. Carlson, R. A. (1997). Experienced Cognition. Mahwah, NJ: Lawrence Erlbaum Associates. Chalmers, D. (1996). The conscious mind. Oxford: Oxford University Press. Crick, F., & Koch, C. (1998). Consciousness and neuroscience. Cerebral Cortex, 8, 97-107. Damasio, A. R. (2000). A neurobiology for consciousness. In T. Metzinger (Ed.), Neural correlates of consciousness Cambridge, MA: The MIT Press. Dienes, Z., & Berry, D. (1997). Implicit learning: Below the subjective threshold. Psychonomic Bulletin and Review, 4, Dennett, D. C. (1991). Consciousness explained. Boston: Little, Brown and Company. Edelman, G. M., & Tononi, G. (2000). Reentry and the dynamic core: Neural correlates of conscious experience. In T. Metzinger (Ed.), Neural correlates of consciousness. Cambridge, MA: The MIT Press. Merikle, P. M., Smilek, D., & Eastwood, J. D. (2001). Perception without awareness: perspectives from cognitive psychology. Cognition, 79, 115-134. Nelson, T. O. (1996). Consciousness and metacognition. American Psychologist, 51, 102-116. Rosenthal, D. M. (1993). Thinking that one thinks. In M. Davies, & G. W. Humphreys (Eds.), Consciousness: Psychological and philosophical essays. Oxford: Blackwell. Searle, J. R. (1992). The rediscovery of the mind. Cambridge, MA: The MIT Press. Schneider, W., & Pimm-Smith, M. (1997). Consciousness as a message aware control mechanism to modulate cognitive processing. J. Cohen, & J. Schooler (Eds.), Scientific approaches to consciousness: The 25th Carnegie Symposium on Cognition. Mahwah, NJ: Erlbaum.

Resting state EEG in patients with disorders of consciousness (DOC) is characterized by an increase of power in the delta frequency band and a concurrent decrease in the alpha range, equivalent to a weakening or disappearance of the alpha peak. Prolongation of Intrinsic Neural Timescales (INTs) is also associated with DOCs. Together, this raises the question whether the decreased alpha peak relates to the prolonged INTs and, importantly, how that can be used for diagnosing the state of consciousness in DOC individuals. Analyzing resting state EEG recordings from both healthy subjects and DOC patients, we measure INTs through autocorrelation window (ACW) and utilize peak analysis to quantify the weakening of the alpha peak. First, we replicate previous findings of prolonged ACW in DOC patients. We then identify significantly lower alpha peak measures in DOC compared to controls. Interestingly, spectral peaks shift from the alpha to the theta range in several DOC subjects while such change is absent in healthy controls. Next, our study reveals a close relationship between ACW and alpha peak in both healthy and DOC subjects, a correlation that holds for theta peaks in DOC. Further, the prolonged ACW correlates with the state of consciousness, as quantified by the Coma Recovery Scale-Revised (CRS-R), and mediates the relationship between theta peak and CRS-R. Finally, through split analyses and machine learning, we show that ACW and alpha peak measures conjointly distinguish healthy controls and DOC patients with high accuracy (95.5%). In conclusion, we demonstrate that the prolongation of ACW, together with spectral peak measures, holds promise to serve as additional EEG biomarkers for diagnosing the state of consciousness in DOC subjects.

OPINION article Front. Hum. Neurosci., 19 July 2013Sec. Cognitive Neuroscience Volume 7 - 2013 | https://doi.org/10.3389/fnhum.2013.00387

Consciousness has become a legitimate theme of neuroscientific discourse over the last two decades. Neuroscientific investigation seeking neural correlates of consciousness (NCC) has ranged from the neuronal level to the system level. Regarding system level studies, there is a large body of evidence supporting the idea that functional connectivity studies can help in examining NCC. Functional connectivity studies have suggested the involvement of the thalamo-cortical, frontoparietal, and other cortico-cortical connectivity under anesthetic-induced unconsciousness and in disorders of consciousness. Likewise, effective connectivity has been used to investigate the causal interactions among elements of functional connectivity in various consciousness states, and provided a deeper understanding of NCC. Moreover, as an extended version of connectivity studies, complex network methods have also been used for studies on NCC. In this review, we focused on the aspect of the brain system level of NCC including functional and effective connectivity networks from methodological perspectives. In addition, as for states of consciousness, anesthetic-induced unconsciousness and disorders of consciousness are the main subjects. This review discusses what we have learned from recent studies about the exploration of human brain connectivity on consciousness and its neural correlates.

Chapter 13 - Disorders of Consciousness

Consciousness or conscious experience is a mental phenomenon that is familiar to all of us, but the way in which it is produced escapes us to a large extent. Each person has a vague idea of what it means to be conscious, but consciousness is rather hard to define, albeit easy to identify. It is that function of the brain that makes us conscious of external or internal stimuli and of our thoughts regarding these subjective experiences. Conscious experience is a first-person perspective of mental states and events tracking as they unfold. It includes mental phenomena such as a perception, emotion, memory, idea, continuous temporal sequence of events. A mental process and its adjoining neurophysiological phenomena represent two aspects of the same event. We have direct access to the mental aspect, while we can observe the neurophysiological aspect only when we study the event as a biological process. The psychological study of consciousness describes the special properties of this brain function, its origin and utility in the global economy of an animal organism. The neurobiological study aims to find the neural correlates of consciousness, aims to establish causal relations between the neural phenomena and the different conscious states. Lastly, the formulation of an explanatory theory can provide a satisfactory understanding of the phenomenon. This review aims to bring some clarification in the field of consciousness, selecting the hypotheses which mostly fulfill the requirements, in order to be confirmed as explanatory theories. A valuable test for confirming an explanatory hypothesis is its predictive power. Using this criterion we have evaluated comparatively, some of the proposed explaining hypotheses.

In late 20th century D. Chalmers came to the conclusion that consciousness is redundant in relation to the brain functioning and he called it the hard problem of consciousness. In this article a fusion of existentialism and quantum theories of consciousness will be proposed, with the result being a neurophenomenological theory of consciousness Quantum brain and Nothingness. An important base for the paper is the idea of direct connection between the hard problem of consciousness and the problem of free will that allows us to build a “bridge” between existential philosophy and the hard problem of consciousness. The main ideas of neurophenomenological theory of consciousness will contain the following: At present moment brain can be simultaneously in multiple states, because of the significant quantum effects that influencing neuron impulses. From the third person’s perspective the quantum brain looks like physical object, but in reality (i.e. “from the inside”, “brain for brain” or brain as “thing-in-itself”) quantum brain is consciousness. It means that the conscious and quantum neuronal processes are the same “something” that can be observed both from inside and from outside. Because of that consciousness exists simultaneously in multiple states. Further free “i” in the continuously processes of selection of one of the possible state of consciousness and automatically chooses one of the possible state of the quantum brain, causing collapse of its wave function as a result. Furthermore, consciousness is “quantum brain for quantum brain” and “i” that is in the continuous process of collapsing of brain’s wave function. Quantum states of brain are pressuring “i” requiring its own realization. This “pressure” and particular quantum states of the brain are represented as multitude of qualia for “i”. As a result, consciousness is emergent interaction of “i” and quantum states of the brain.

Neuromodulation of the conscious state following severe brain injuries

Identifying the neuronal markers of consciousness is key to supporting the different scientific theories of consciousness. Neuronal markers of consciousness can be defined to reflect either the brain signatures underlying specific conscious content or those supporting different states of consciousness, two aspects traditionally studied separately. In this paper, we introduce a framework to characterize markers according to their dynamics in both the "state" and "content" dimensions. The 2D space is defined by the marker's capacity to distinguish the conscious states from non-conscious states (on the x-axis) and the content (e.g. perceived versus unperceived or different levels of cognitive processing on the y-axis). According to the sign of the x- and y-axis, markers are separated into four quadrants in terms of how they distinguish the state and content dimensions. We implement the framework using three types of electroencephalography markers: markers of connectivity, markers of complexity, and spectral summaries. The neuronal markers of state are represented by the level of consciousness in (i) healthy participants during a nap and (ii) patients with disorders of consciousness. On the other hand, the neuronal markers of content are represented by (i) the conscious content in healthy participants' perception task using a visual awareness paradigm and (ii) conscious processing of hierarchical regularities using an auditory local-global paradigm. In both cases, we see separate clusters of markers with correlated and anticorrelated dynamics, shedding light on the complex relationship between the state and content of consciousness and emphasizing the importance of considering them simultaneously. This work presents an innovative framework for studying consciousness by examining neuronal markers in a 2D space, providing a valuable resource for future research, with potential applications using diverse experimental paradigms, neural recording techniques, and modeling investigations.