How Consciousness Works

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

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.

The aim of the study was to investigate differences in cortical networks based on the state of consciousness. Five subjects performed a serial-awakening paradigm with electroencephalography (EEG) recordings. We considered four states of consciousness: (1) non-rapid eye movement (NREM) sleep with no conscious experience, (2) NREM sleep with conscious experience, (3) rapid eye movement (REM) sleep with conscious experience, and (4) wakefulness. We applied graph theoretical analysis to explore the cortical connectivity and network properties in five frequency bands. Connectivity between EEG channels was evaluated with the weighted phase lag index (wPLI). The characteristic path length, transitivity, and clustering coefficient were computed to evaluate functional integration and segregation of the associated brain network. There were no significant differences in wPLI among the four states of consciousness. In the beta band, functional integration in wakefulness was higher than in NREM sleep. Regarding functional segregation, in the theta band, transitivity and clustering coefficient in NREM sleep with no conscious experience were stronger than in wakefulness or REM sleep, but clustering in the beta band showed an opposite effect. The observed differences may be related to cortical bistability and add to previously observed neural correlates of consciousness.

EDITORIAL article Front. Psychol., 18 February 2015Sec. Consciousness Research https://doi.org/10.3389/fpsyg.2015.00166

Emotional states of consciousness, or what are typically called emotional feelings, are traditionally viewed as being innately programmed in subcortical areas of the brain, and are often treated as different from cognitive states of consciousness, such as those related to the perception of external stimuli. We argue that conscious experiences, regardless of their content, arise from one system in the brain. In this view, what differs in emotional and nonemotional states are the kinds of inputs that are processed by a general cortical network of cognition, a network essential for conscious experiences. Although subcortical circuits are not directly responsible for conscious feelings, they provide nonconscious inputs that coalesce with other kinds of neural signals in the cognitive assembly of conscious emotional experiences. In building the case for this proposal, we defend a modified version of what is known as the higher-order theory of consciousness.

This article is an attempt to conceptualize such structures of the experience of consciousness as temporality and subjectivity in their interconnectedness. The article questions the assumption that the location of experience in time and the belonging of experience to a particular subject should be interpreted as invariant characteristics of the experience of consciousness. The author investigates the counter-assumption according to which these characteristics are not assumed to be necessary for any state of consciousness. This assumption is tested using phenomenological analysis of such extraordinary states of consciousness as the psychotic experience of schizophrenic patients and the meditative experience of advanced practitioners. The similarity of these states of consciousness is that both can be characterized in terms of the deformation of the subject's experience of living time and self. Clarifying the parameters that make up the habitual experience of the subjectivity of everyday experience, the author hypothesizes that the key factor in temporal-personal changes are shifts in the subject's affectation, the ultimate values of which lead to the elimination of subject-object dualism and temporality of the experience of consciousness. The arbitrariness of these shifts is understood as the main condition for the traumatization of these changes in the experience of consciousness. At the same time, the article raises the question of the phenomenological status of the state of non-dual and atemporal consciousness, which, due to its deprivation of any intensional content, is likened to the state of dreamless sleep and conceptualized in modern cognitive sciences as "pure consciousness". The resulting state of consciousness is proposed to be thought of as a "zero point" of consciousness, over which, due to affectation, the usual structures of temporality and subject-object dichotomy are superimposed.

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

Exploring the limits to our understanding of whether fish feel pain.

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

The problem of consciousness is mostly regarded as identical to the mind-body problem. According to Chalmers’ philosophical arguments, the hard problem of consciousness lies in establishing and explaining the link between physical processes and conscious experiences, via psychological processes. A brief history of various theories of consciousness is given and a selection of theories are tested against Zeman’s three fundamental intuitions and Chalmers’ controversial zombie argument. The hard problem of consciousness is further described using Levine’s notion of an explanatory gap between physical matter and conscious experience, through the first and third persons. Various states, contents, levels and processes of consciousness are summarised, including Damasio and Meyer’s dual perspective for defining consciousness. Tart’s three definitions do not entirely describe altered states of consciousness. While the challenge of finding the core function of human and animal sleep remains unknown when tested under the null hypothesis, studies on the neural correlates of consciousness during meditation have revealed neuroplasticity effects. The synchrony of gamma brain oscillations reflecting various styles of meditation or attention, also known as the binding problem, may be related to conscious experiences. This binding problem with gamma brain oscillatory synchronization also arises in relation to sensory awareness or perception, affecting the perception of time and hallucinatory experiences in various disorders of consciousness such as severe schizophrenic and deja vu (in healthy or epileptic) patients. In conjunction with medication treatments, music therapy is often useful in accelerating the healing process in most such disorders of consciousness. It is still unknown how this sensory awareness to music is perceived in medicated patients suffering from disorders of consciousness. More clinically elusive are near death experiences, in which consciousness persists independently of brain function, where there is no scientific basis for such consciousness to exist and no physiological or psychological model that can explain it. Near death experiences can be regarded as a special state of consciousness, which provides further evidence that the consciousness problem may be very close to the mind-body problem that originates in Descartes’ classic theory of dualism and is transformed into Chalmers’ contemporary theory of natural dualism. The final section of this chapter offers an overview of all invited chapters.

Sleep and anesthesia entail alterations in conscious experience. Conscious experience may be absent (unconsciousness) or take the form of dreaming, a state in which sensory stimuli are not incorporated into conscious experience (disconnected consciousness). Recent work has identified features of cortical activity that distinguish conscious from unconscious states; however, less is known about how cortical activity differs between disconnected states and normal wakefulness. We employed transcranial magnetic stimulation–electroencephalography (TMS–EEG) over parietal regions across states of anesthesia and sleep to assess whether evoked oscillatory activity differed in disconnected states. We hypothesized that alpha activity, which may regulate perception of sensory stimuli, is altered in the disconnected states of rapid eye movement (REM) sleep and ketamine anesthesia. Compared to wakefulness, evoked alpha power (8–12 Hz) was decreased during disconnected consciousness. In contrast, in unconscious states of propofol anesthesia and non-REM (NREM) sleep, evoked low-gamma power (30–40 Hz) was decreased compared to wakefulness or states of disconnected consciousness. These findings were confirmed in subjects in which dream reports were obtained following serial awakenings from NREM sleep. By examining signatures of evoked cortical activity across conscious states, we identified novel evidence that suppression of evoked alpha activity may represent a promising marker of sensory disconnection.

Detecting and interpreting conscious experiences in behaviorally non-responsive patients

Progress is being made in understanding how brain mechanisms generate conscious experience. Simple conscious experiences such as sensations of colors, shapes, and sounds require only neural representations as patterns of firing that result from sensory inputs and internal processing. More complicated conscious experiences, such as awareness of reading in a chair in a room, require the amalgamation of sensations and images into more complex representations through binding into semantic pointers. Recursive binding—bindings of bindings of bindings—can produce the most complicated kinds of conscious experience of which humans are capable, taking people from feelings to awareness to self-awareness. Consciousness is limited because recursive binding and competition among the resulting semantic pointers depend on processing by many neurons.

Consciousness is difficult to pin down. Most human beings go about their days with full and more or less uninterrupted consciousness, without contemplating their own (or other peoples’) conscious states. To be in the world, and accomplish great acts takes little metaawareness of consciousness, but in the study of consciousness our inability to think outside of our conscious states creates controversies at the conceptual and methodological levels. As Victor Lamme states (2006), even when we set aside the more difficult (or more poorly defined) questions about conscious experience to focus on finding the neural correlates of consciousness (NCC), we face immense difficulties (Lamme, 2006, p. 494). Experiments designed to find the NCC often involve the manipulation of conscious states through anesthesia, the study of sleep, or brain lesion studies (Lamme, 2006, p. 494). However, even in the case of anesthesia, where we can voluntarily induce a reversible altered state of consciousness there does not seem to be a clear dividing line between consciousness and unconsciousness with any of the processed electroencephalogram (EEG) signals (Guzeldere, 1998, p. 1) such that the conscious and unconscious states are still confirmed behaviorally (Lamme, 2006, p. 494). This leads to a problem, as it must be decided what "behavioral measures 'count' as evidence for the subject having conscious experience (p. 494)" a problem that is not so simple as the ability to speak and respond, as will be more clear in a later discussion of intraoperative awareness. Furthermore, Guven Guzeldere points to the difficulty of defining what "the problem of consciousness" is, within and "across disciplinary boundaries (Guzeldere, p. 7)." The problems that philosophers of consciousness, cognitive scientists and neuroscientists address when they study consciousness are not inevitably going to be identical, but are shaped by disciplinary perspectives, methods and technologies. Therefore, in this paper I am going to contrast two similar models of consciousness, Giulio Tononi’s Integrated Information Theory and Daniel Dennett’s Multiple Drafts Model, and evaluate them against the mechanisms of several anesthetics (Propofol, ketamine, and the inhalation anesthetics, including xenon), which will be summarized by a review of the literature. I have two goals in mind with this project: first, I have chosen two very similar models in order to demonstrate how small differences- such as Tononi’s engagement with the concept of qualia and Dennett’s deconstruction of it-- have large implications for what types of knowledge are possible when these models are

When investigating the neural correlates of consciousness, neuroscientists distinguish between ‘‘conscious state’’ (being awake as opposed to asleep or in a coma), which is regulated by brainstem and thalamic nuclei, and ‘‘conscious representation’’ (awareness of specific phenomenal experience). The advent of functional brain imaging techniques, especially fMRI, enables the noninvasive inquiries of the mechanisms underlying conscious experience, particularly in the visual system. To date, most experimental paradigms designed to study consciousness contrast the response during conscious visual experience with the response during unconscious visual experience (the so-called blindsight phenomenon), or record patterns of brain activation during binocular rivalry, perception of bistable figures, and visual mental imagery. The current data suggest that activity in high-level areas of the ventral visual pathway, but not in V1, are necessary for conscious visual experience. Moreover, visual awareness requires parietal and prefrontal regions (for a recent review, see Rees, Kreiman, & Koch, 2002). The neural correlates of conscious vision, therefore, parallel the distributed cortical networks that modulate visual attention and visual imagery. As most researchers confuse ‘‘awareness’’ with ‘‘consciousness,’’ the reported differential activity during consciousness is currently indistinguishable from that of other higher cognitive functions. In his article, ‘‘Functional fMRI and the Study of Human Consciousness,’’ Dan Lloyd uniquely combines a conceptual analysis of consciousness with neuroscientific methods, in order to characterize the neural manifestations of consciousness (Lloyd, 2002). Lloyd adopts Husserl’s criteria, according to which the phenomenology of consciousness is based on three essential principles: intentionality (the external world as it is experienced and not as it is); superposition (sensory and nonsensory properties are present in perception); and temporality (all objects share perception of present, past, and anticipated future). If indeed these aspects of consciousness are implemented in the brain, the empirical evidence should include temporal flux (with passing time, the multivariate differences between images should increase) and superposition (images sharing task or stimulus conditions should be similar). Lloyd’s methodological approach includes three constraints. First, time points in a scan series are considered individually, because temporality implies that consciousness at each point in time is distinct from the preceding and the proceeding points. Second, subjects are considered individually, because intersubject averaging could eliminate individual expression of consciousness. Finally, brain states are considered globally, seeking distributed patterns of activation that encompass large cortical areas, rather than assuming localized responses. To test his predictions, Lloyd reanalyzes four data sets (Hazeltine, Poldrack, & Gabrieli, 2000; Ishai, Ungerleider, Martin, & Haxby, 2000; Mechelli, Friston, & Price, 2000; Postle, Berger, Taich, & D’Esposito, 2000) provided by The fMRI Data Center. The studies, published in the December 2000 issue of the Journal of Cognitive Neuroscience, included a variety of cognitive tasks (target tracking, passive viewing, delayed matching, reading, and spatial working memory), stimuli (faces, objects, words, pseudowords, 2-D arrays of squares, colored circles), and motor responses (button presses and saccades). Needless to say, none of the original studies was designed for or aimed at underpinning the neural mechanisms of ‘‘neurophenomenology.’’ Nevertheless, Lloyd preprocesses and reanalyzes the raw data to test his predictions about the general structures of consciousness, which by their nature are task and stimulus independent. Using multivariate distance analysis and artificial neural networks, he shows a time–distance effect (i.e., as the time series progressed, the distance between images increased) and that the past and future brain states, retention and protention, respectively, are embedded in present brain states. As time passes, suggests Lloyd, the brain is changing ‘‘globally, incrementally, and monotonically.’’ Previous fMRI studies of consciousness compared one state of awareness with another, assumed localization, and ignored the temporal flux. Lloyd’s original approach proposes methodological and conceptual advantages. Traditionally, fMRI data analysis focused on two parameters, namely the spatial extent of the activation and the amplitude of the response within an activated region. The data are usually displayed as statistical maps indicating the location and size of significant activation, and graphs or histograms showing the percent fMRI signal change. Given the spatial and temporal resolution of the technique, extracting temporal information about the ‘‘tripartite temporality’’ (i.e., the experienced present of National Institutes of Health