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PubMed1999

Accounting for the computational basis of consciousness: a connectionist approach.

This paper argues for an explanation of the mechanistic (computational) basis of consciousness that is based on the distinction between localist (symbolic) representation and distributed representation, the ideas of which have been put forth in the connectionist literature. A model is developed to substantiate and test this approach. The paper also explores the issue of the functional roles of consciousness, in relation to the proposed mechanistic explanation of consciousness. The model, embodying the representational difference, is able to account for the functional role of consciousness, in the form of the synergy between the conscious and the unconscious. The fit between the model and various cognitive phenomena and data (documented in the psychological literatures) is discussed to accentuate the plausibility of the model and its explanation of consciousness. Comparisons with existing models of consciousness are made in the end.

Cognition↗

PubMed2001

Consciousness during dreams.

Two aspects of consciousness are first considered: consciousness as awareness (phenomenological meaning) and consciousness as strategic control (functional meaning). As to awareness, three types can be distinguished: first, awareness as the phenomenal experiences of objects and events; second, awareness as meta-awareness, i.e., the awareness of mental life itself; third, awareness as self-awareness, i.e., the awareness of being oneself. While phenomenal experience and self-awareness are usually present during dreaming (even if many modifications are possible), meta-awareness is usually absent (apart from some particular experiences of self-reflectiveness) with the major exception of lucid dreaming. Consciousness as strategic control may also be present in dreams. The functioning of consciousness is then analyzed, following a cognitive model of dream production. In such a model, the dream is supposed to be the product of the interaction of three components: (a) the bottom-up activation of mnemonic elements coming from LTM systems, (b) interpretative and elaborative top-down processes, and (c) monitoring of phenomenal experience. A feedback circulation is activated among the components, where the top-down interpretative organization and the conscious monitoring of the oneiric scene elicitates other mnemonic contents, according to the requirements of the dream plot. This dream productive activity is submitted to unconscious and conscious processes.

Awareness↗

PubMed2001

The brain basis of a "consciousness monitor": scientific and medical significance.

Surgical patients under anesthesia can wake up unpredictably and be exposed to intense, traumatic pain. Current medical techniques cannot maintain depth of anesthesia at a perfectly stable and safe level; the depth of unconsciousness may change from moment to moment. Without an effective consciousness monitor anesthesiologists may not be able to adjust dosages in time to protect patients from pain. An estimated 40,000 to 200,000 midoperative awakenings may occur in the United States annually. E. R. John and coauthors present the scientific basis of a practical "consciousness monitor" in two articles. One article is empirical and shows widespread and consistent electrical field changes across subjects and anesthetic agents as soon as consciousness is lost; these changes reverse when consciousness is regained afterward. These findings form the basis of a surgical consciousness monitor that recently received approval from the U.S. Food and Drug Administration. This may be the first practical application of research on the brain basis of consciousness. The other John article suggests theoretical explanations at three levels, a neurophysiological account of anesthesia, a neural dynamic account of conscious and unconscious states, and an integrative field theory. Of these, the neurophysiology is the best understood. Neural dynamics is evolving rapidly, with several alternative points of view. The field theory sketched here is the most novel and controversial.

Anesthesia, General↗

PubMedDate not supplied

Theory of the organism-environment system: IV. The problem on mental activity and consciousness.

The present article is an attempt to bring together the development of mental activity and consciousness in the framework of the organism-environment theory (Jarvilehto, 1998a, 1998b, 1999); the main question is how the development of mental activity and consciousness can be formulated if the starting point is not the separation of man and environment as in traditional cognitive psychology, but a unitary organism-environment system. According to the present formulation, mental activity is conceived as activity of the whole organism-environment system and connected to the general development of life as a specific form of an organism-environment system comprising neurons. The advent of consciousness is regarded as a result of co-operation of such organism-environment systems. Consciousness is based on cooperation for the achievement of common results, and shared by the cooperating individuals (general consciousness), although each individual also makes it concrete from the perspective of his/her own body in the act of participation in common results (personal consciousness). Language is the means of formation of the cooperative system in the achievement of common results, and it is suggested that the use of language is related more to the type of cooperative system and intended common results than to any symbolic representation of the world. It is claimed that on this basis it is possible to develop psychology which takes seriously the concepts of mental activity and consciousness in the description of human action, but does not reduce these concepts either to biological or social factors. The present formulation should be regarded more as a conceptual outline than as a full-blown theory.

Aging↗

PubMed1992

Microinjection of L-glutamate into the nucleus tractus solitarii increases arterial pressure in conscious rats.

Microinjection of L-glutamate into the nucleus tractus solitarii (NTS) of anesthetized rats produces a fall in mean arterial pressure (MAP) similar to that observed during activation of baroreceptor afferents. In the present study we examined the effect of bilateral microinjections of L-glutamate through chronically implanted cannulae in the NTS of conscious freely moving rats. Group I (n = 6) was studied under conscious conditions and 24 h later the rats were anesthetized with urethane and the effects of L-glutamate re-examined. In conscious rats, L-glutamate (30 pmol to 5 nmol/100 nl) produced dose-dependent increases in MAP (+37 +/- 7 mmHg, 5 nmol), whereas under urethane anesthesia falls in MAP were observed (-11 +/- 3 mmHg, 5 nmol). Group II (n = 7) was studied under conscious conditions and 1 h later the rats were anesthetized with chloralose and the effects of L-glutamate re-examined. In this group of conscious rats L-glutamate (300 pmol to 5 nmol/100 nl) also produced dose-dependent increases in MAP (+37 +/- 5 mmHg, 5 nmol), whereas under chloralose anesthesia a dose-dependent depressor response was observed (-33 +/- 6 mmHg, 5 nmol). Saline microinjections into the NTS of conscious and anesthetized rats produced negligible effects. These data demonstrate that microinjection of L-glutamate into the NTS of rats produces a pressor response in conscious animals in contrast to depressor responses in animals anesthetized with chloralose or urethane.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗

PubMed2005

A model of the hierarchy of behaviour, cognition, and consciousness.

Processes comparable in important respects to those underlying human conscious and non-conscious processing can be identified in a range of species and it is argued that these reflect evolutionary precursors of the human processes. A distinction is drawn between two types of processing: (1) stimulus-based and (2) higher-order. For 'higher-order,' in humans the operations of processing are themselves associated with conscious awareness. Conscious awareness sets the context for stimulus-based processing and its end-point is accessible to conscious awareness. However, the mechanics of the translation between stimulus and response proceeds without conscious control. The paper argues that higher-order processing is an evolutionary addition to stimulus-based processing. The model's value is shown for gaining insight into a range of phenomena and their link with consciousness. These include brain damage, learning, memory, development, vision, emotion, motor control, reasoning, the voluntary versus involuntary debate, and mental disorder.

Affect↗

PubMed2006

Is conscious perception gradual or dichotomous? A comparison of report methodologies during a visual task.

In a recent article, [Sergent, C. & Dehaene, S. (2004). Is consciousness a gradual phenomenon? Evidence for an all-or-none bifurcation during the attentional blink, Psychological Science, 15(11), 720-729] claim to give experimental support to the thesis that there is a clear transition between conscious and unconscious perception. This idea is opposed to theoretical arguments that we should think of conscious perception as a continuum of clarity, with e.g., fringe conscious states [Mangan, B. (2001). Sensation's ghost-the non-sensory "fringe" of consciousness, Psyche, 7, 18]. In the experimental study described in this article, we find support for this opposite notion that we should have a parsimonious account of conscious perception. Our reported finding relates to the hypothesis that there is more than one perceptual threshold [Merikle, P.M., Smilek, D. & Eastwood, J.D. (2001). Perception without awareness: perspectives from cognitive psychology, Cognition, 79, 115-134], but goes further to argue that there are different "levels" of conscious perception.

Adolescent↗

PubMed2005

Consciousness, epilepsy, and emotional qualia.

The last decade has seen a renaissance of consciousness studies, witnessed by the growing number of scientific investigations on this topic. The concept of consciousness is central in epileptology, despite the methodological difficulties concerning its application to the multifaced ictal phenomenology. The authors provide an up-to-date review of the neurological literature on the relationship between epilepsy and consciousness and propose a bidimensional model (level vs contents of consciousness) for the description of seizure-induced alterations of conscious states, according to the findings of recent neuroimaging studies. The neurophysiological correlates of ictal loss and impairment of consciousness are also reviewed. Special attention is paid to the subjective experiential states associated with medial temporal lobe epilepsy. Such ictal phenomenal experiences are suggested as a paradigm for a neuroscientific approach to the apparently elusive philosophical concept of qualia. Epilepsy is confirmed to represent a privileged window over basic neurobiological mechanisms of consciousness.

Consciousness↗

PubMed2001

Introspective physicalism as an approach to the science of consciousness.

Most 'theories of consciousness' are based on vague speculations about the properties of conscious experience. We aim to provide a more solid basis for a science of consciousness. We argue that a theory of consciousness should provide an account of the very processes that allow us to acquire and use information about our own mental states - the processes underlying introspection. This can be achieved through the construction of information-processing models that can account for 'Type-C' processes. Type-C processes can be specified experimentally by identifying paradigms in which awareness of the stimulus is necessary for an intentional action. The Shallice (1988b) framework is put forward as providing an initial account of Type-C processes, which can relate perceptual consciousness to consciously performed actions. Further, we suggest that this framework may be refined through the investigation of the functions of prefrontal cortex. The formulation of our approach requires us to consider fundamental conceptual and methodological issues associated with consciousness. The most significant of these issues concerns the scientific use of introspective evidence. We outline and justify a conservative methodological approach to the use of introspective evidence, with attention to the difficulties historically associated with its use in psychology.

Awareness↗

PubMed2002

Conscious and unconscious uses of memory in multiple sclerosis.

Conscious and unconscious uses of memory and priming were studied in 30 patients with multiple sclerosis (MS) and 15 normal control (NC) subjects. MS patients were classified into two subgroups according to their cognitive status; 15 of them were cognitively deteriorated (the MS-D group) and 15 cognitively preserved (the MS-P group). A process dissociation procedure [J. Mem. Lang. 30 (1991) 513] was used to separate conscious and unconscious memory performance in a word stem completion task. The results showed that the MS-D group had deficient conscious memory performance, but had intact unconscious memory as well as priming. The MS-P group showed normal conscious and unconscious uses of memory and priming. Thus, in MS-related cognitive decline, conscious memory seems to be vulnerable, whereas unconscious memory remains intact. The results provide neuropsychological support for the distinction between conscious and unconscious memory processes. Moreover, the results show the importance of studying cognitively homogenous MS groups as opposed to heterogenous ones, in order to find the underlying mechanisms of memory deficits in MS. Interestingly, the neural systems needed for the unconscious use of memory do not seem to deteriorate even in MS patients with deficient overall cognitive capacity. This finding encourages the development of future rehabilitation programs, suggesting that unconscious remembering might help MS patients with deficient conscious memory to cope with their daily activities.

Adult↗

PubMed2005

Functional neuroimaging during altered states of consciousness: how and what do we measure?

The emergence of functional neuroimaging has extended the doctrine of functional specificity of the brain beyond the primary stages of perception, language, and motor systems to high-level cognitive, personality, and affective systems. This chapter applies functional magnetic resonance imaging to another high-level realm of cognition and neurology to characterize cortical function in patients with disorders of consciousness. At first pass, this objective appears paradoxical because conventional investigations of a cognitive process require experimental manipulation. For example, to map the location of language-sensitive cortex, a language-related task is performed according to a temporal sequence that alternates the task with rest (no-task) periods. Application of this approach to the study of consciousness would require that levels of consciousness be similarly varied, this is an unlikely technique. Alternatively, another strategy is presented here where the focus is on functional brain activity elicited during various passive stimulations of patients who are minimally conscious. Comparisons between patients with altered states of consciousness due to brain injury and healthy subjects may be employed to infer readiness and potential to sustain awareness. As if a behavioral microscope, fMRI enables a view of occluded neural processes to inform medical practitioners about the health of the neurocircuity-mediating cognitive processes. An underlying point of view is that assessment of recovery potential can be enhanced by neuroimaging techniques that reveal the status of residual systems specialized for essential cognitive and volitional tasks for each patient. Thus, development of imaging techniques that assess the functional status of individual unresponsive patients is a primary goal. The structural integrity of injured brains is often compromised depending on the specific traumatic event, and, therefore, images cannot be grouped across patients, as is the standard practice for investigations of cognitive systems in healthy volunteers. This chapter addresses these challenges and discusses technique adaptations associated with passive stimulation, paradigm selection, and individual patient assessments, where there is "zero tolerance for error," and confidence in the results must meet the highest standards of care. Similar adaptations have been previously developed for the purpose of personalized planning for neurosurgical procedures by mapping the locations of essential functional systems such as language, perception, and sensory-motor functions for each individual patient. Rather than addressing the question of "how does the brain do consciousness" with these techniques, this chapter presents methods for assessment of neurocognitive health in specific patients with disorders of consciousness.

Attention↗

PubMed2005

Machine consciousness.

The work from several laboratories on the modeling of consciousness is reviewed. This ranges, on one hand, from purely functional models where behavior is important and leads to an attribution of consciousness to, on the other hand, material work closely derived from the information about the anatomy of the brain. At the functional end of the spectrum, applications are described specifically directed at a job-finding problem, where the person being served should not discern between being served by a conscious human or a machine. This employs an implementation of global workspace theories. At the material end, attempts at modeling attentional brain mechanisms, and basic biochemical processes in children are discussed. There are also general prescriptions for functional schemas that facilitate discussions for the presence of consciousness in computational systems and axiomatic structures that define necessary architectural features without which it would be difficult to represent sensations. Another distinction between these two approaches is whether one attempts to model phenomenology (material end) or not (functional end). The former is sometimes called "synthetic phenomenology." The upshot of this chapter is that studying consciousness through the design of machines is likely to have two major outcomes. The first is to provide a wide-ranging computational language to express the concept of consciousness. The second is to suggest a wide-ranging set of computational methods for building competent machinery that benefits from the flexibility of conscious representations.

Consciousness↗

PubMed2005

General anesthesia and the neural correlates of consciousness.

The neural correlates of consciousness must be identified, but how? Anesthetics can be used as tools to dissect the nervous system. Anesthetics not only allow for the experimental investigation into the conscious-unconscious state transition, but they can also be titrated to subanesthetic doses in order to affect selected components of consciousness such as memory, attention, pain processing, or emotion. A number of basic neuroimaging examinations of various anesthetic agents have now been completed. A common pattern of regional activity suppression is emerging for which the thalamus is identified as a key target of anesthetic effects on consciousness. It has been proposed that a neuronal hyperpolarization block at the level of the thalamus, or thalamocortical and corticocortical reverberant loops, could contribute to anesthetic-induced unconsciousness. However, all anesthetics do not suppress global cerebral metabolism and cause a regionally specific effect on thalamic activity. Ketamine, a so-called dissociative anesthetic agent, increases global cerebral metabolism in humans at doses associated with a loss of consciousness. Nevertheless, it is proposed that those few anesthetics not associated with a global metabolic suppression effect might still have their effects on consciousness mediated at the level of thalamocortical interactions, if such agents scramble the signals associated with normal neuronal network reverberant activity. Functional and effective connectivity are analysis techniques that can be used with neuroimaging to investigate the signal scrambling effects of various anesthetics on network interactions. Whereas network interactions have yet to be investigated with ketamine, a thalamocortical and corticocortical disconnection effect during unconsciousness has been found for both suppressive anesthetic agents and for patients who are in the persistent vegetative state. Furthermore, recovery from a vegetative state is associated with a reconnection of functional connectivity. Taken together these intriguing observations offer strong empirical support that the thalamus and thalamocortical reverberant network loop interactions are at the heart of the neurobiology of consciousness.

Anesthesia, General↗

PubMed2001

Defining the states of consciousness.

Consciousness remains an elusive concept due to the difficulty to define what has been regarded for many years as a subjective experience, therefore irrelevant for scientific study. Recent development in this field of research has allowed to provide some new insight to a possible way to define consciousness. Going through the extensive literature in this domain, several perspectives are proposed to define this concept. (1) Consciousness and Attention may not reflect the same process. (2) Consciousness during wake and sleep may not involve the same mechanisms. (3) Besides physiological states of consciousness, human beings can experience modified states of consciousness either by self-training (transcendental meditation, hypnosis, etc.) or by drug intake (hallucinogens, anaesthetics, etc.). Altogether, we address the question of a more precise terminology, given the theoretical weight words can convey. To this respect, we propose different definitions for concepts like consciousness, vigilance, arousal and alertness as candidates to separate functional entities.

Animals↗

PubMed1998

Anesthesia, consciousness and hydrophobic pockets--a unitary quantum hypothesis of anesthetic action.

1. A consensus view holds that anesthetics act by van der Waals forces in hydrophobic pockets of select brain proteins to ablate consciousness. 2. What is consciousness? Enigmatic features of consciousness (e.g. 'qualia', binding, non-computability, pre-conscious-->conscious transition, nondeterministic free will) may be explained by the occurrence of quantum coherent states in the brain. 3. Van der Waals electron pair couplings (London forces) in hydrophobic pockets in non-anesthetic (conscious) conditions are a particular type of quantum capable of supporting macroscopic quantum coherence. 4. The mechanism of anesthetics may be to inhibit electron mobility and London forces necessary for quantum states and consciousness in hydrophobic pockets of select brain proteins.

Anesthesia↗

PubMed2003

Visual consciousness in health and disease.

Conscious experience is an essential part of normal human life and interaction with the environment. Yet the nature of consciousness and conscious perception remains a mystery. Because of its subjective nature, consciousness has been difficult to investigate scientifically, but clues have been gained through studies involving patients with cortical lesions. During the past decade, the development of event-related fMRI has provided insights into aspects of conscious perception in control subjects and patients with cortical lesions by correlating awareness and performance with neural activity during visual tasks. This article reviews how recent research has advanced understanding of conscious perception, its relationship to neural activity and visual performance, and how this relationship can be altered by visual dysfunction. It also presents recent research about how conscious awareness of vision might be represented at a neural level in the central nervous system.

Attention↗

PubMed2004

Précis of the illusion of conscious will.

The experience of conscious will is the feeling that we are doing things. This feeling occurs for many things we do, conveying to us again and again the sense that we consciously cause our actions. But the feeling may not be a true reading of what is happening in our minds, brains, and bodies as our actions are produced. The feeling of conscious will can be fooled. This happens in clinical disorders such as alien hand syndrome, dissociative identity disorder, and schizophrenic auditory hallucinations. And in people without disorders, phenomena such as hypnosis, automatic writing, Ouija board spelling, water dowsing, facilitated communication, speaking in tongues, spirit possession, and trance channeling also illustrate anomalies of will--cases when actions occur without will or will occurs without action. This book brings these cases together with research evidence from laboratories in psychology to explore a theory of apparent mental causation. According to this theory, when a thought appears in consciousness just prior to an action, is consistent with the action, and appears exclusive of salient alternative causes of the action, we experience conscious will and ascribe authorship to ourselves for the action. Experiences of conscious will thus arise from processes whereby the mind interprets itself--not from processes whereby mind creates action. Conscious will, in this view, is an indication that we think we have caused an action, not a revelation of the causal sequence by which the action was produced.

Consciousness↗

PubMed1997

Consciousness of perception after brain damage.

Disturbances of visual perception after brain damage provide clues to understanding consciousness and the brain. In this article we review six visual disorders in which perception and consciousness are dissociated as a result of brain damage: blindsight, implicit shape perception in apperceptive visual agnosia, covert recognition of faces in prosopagnosia, unconscious perception in neglect and extinction, implicit reading in pure alexia, and implicit object recognition in associative visual agnosia. We consider these six disorders from the standpoint of three main schools of thought concerning consciousness and the brain, namely a localized system for consciousness, consciousness as a state of integration, and consciousness as a property of graded representation. The findings suggest that these syndromes do not share a single mechanism and that it is conceivable that more than one explanation will be necessary both within and across syndromes. We conclude on the basis of the current evidence that it is unlikely that any single brain system is necessary for conscious awareness of perception that does not play a role in perception as well.

Agnosia↗