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PubMed1996

[The physiology of consciousness].

Since 1990, the number of papers on the biological basis of consciousness has increased sharply. Some aspects of consciousness, such as its localization in the brain structure, relation of conscious and unconscious processes, selective attention and the waking state may be analyzed by objective means. According to the model proposed by Dennett and Kinsbourne (1990) and called Multiple Drafts Model, there is no isolated module in the brain structure where consciousness is located. Conscious experience is a serial stream of activity integrating various sources of information. All conscious processes are generated in various parts of the central nervous system and the state of consciousness moves throughout the brain structure. Consciousness is therefore not identical with the global activity of the brain. Information may enter the consciousness or stay out of it in relation to the actual contents of the conscious process. Experimental data supporting this notion were obtained by electrophysiology, positron emission tomography, nuclear magnetic resonance, measuring of blood flow and other metabolic methods. These studies indicate that the state of consciousness is characterized by an increased neuronal activity and they may show which part of the brain is activated at any given moment. Of all brain areas involved in conscious processes, the role of the frontal lobe is widely documented in clinical and physiological papers. Entry of any information into consciousness requires about 350 to 500 ms of neuronal activity. Subjective timing of conscious recognition of events in the outside world is then retroactively returned to the moment when the information enters the neural processing. Recent research indicates that the gap between the humanistic and neurophysiological approach becomes gradually narrowed. Still, we have to keep in mind that the basic question about the ideal or materialistic character of consciousness remains open.

Brain↗
PubMed1979

Three types of consciousness.

It is useful to distinguish three senses of the word 'consciousness'. 'Minimal' consciousness is the occurrence of any mental activity, whether or not the subject is aware of this activity. 'Perceptual' consciousness is perceptual activity. Minimal and perceptual consciousness may be present, yet 'introspective' consciousness be lacking. Introspective consciousness is conceived as it was by Locke and Kant: as perception-like awareness of the subject's own current mental states and activities. It includes introspective consciousness of introspective consciousness itself. A useful model for demystifying and naturalizing introspective consciousness is the subject's proprioceptive awareness of bodily states and activities. Introspective consciousness may be further subdivided into 'reflex' introspective consciousness and 'introspection proper'. The distinction is one of degree: the degree of attention involved. We attach a quite special importance to introspective consciousness and are particularly unwilling to identify it with a purely physical process in the brain. It is suggested, however, that this springs from (a) the fact that what is introspected is taken to be a state or activity of a single thing, the self; and (b) the fact that event-memory is generally only possible if the event remembered was the object of introspective consciousness at the time. Without introspective consciousness, therefore, awareness of a self and the past history of that self is lacking.

Adolescent↗
PubMed1996

[The anatomy of consciousness in domestic animals. Opening address of the 20th Congress of the EVVA in Zürich in memory of Eugen Seiferle].

All living organisms have a consciousness, not only humans. To seek to find humans' consciousness in animals is to seek wrongly. The question must be: "To what extent are prehuman and human consciousness comparable.' Animals have an instinctive sensational consciousness with a partial learning consciousness. It is a purely self-sustaining consciousness. In addition, humans have a spiritual-thinking consciousness, which is predominantly a learning consciousness and is not a pure self-sustaining consciousness. Since human consciousness arose from animals' consciousness, that behaviour in animals which is similar to the thought process in human beings can only be based on sensations. Sensations of pain and fear are not very different in man and animal, because they also belong to the sensation consciousness in humans, but humans have the additional advantage of being able to think about them and to understand their cause and meaning. That is not possible in animals, therefore, animals have to be anaesthetized to protect them from pain. Seiferle recognized this clearly, and my consciousness theory reinforces Seiferle's view, i.e. that consciousness is the central force of the soul. Its afferent forces are perception and sensation; its efferent forces are will, feeling, and deed.

Animals↗
PubMed2001

Consciousness, the brain, and spacetime geometry.

What is consciousness? Conventional approaches see it as an emergent property of complex interactions among individual neurons; however these approaches fail to address enigmatic features of consciousness. Accordingly, some philosophers have contended that "qualia," or an experiential medium from which consciousness is derived, exists as a fundamental component of reality. Whitehead, for example, described the universe as being composed of "occasions of experience." To examine this possibility scientifically, the very nature of physical reality must be re-examined. We must come to terms with the physics of spacetime--as described by Einstein's general theory of relativity, and its relation to the fundamental theory of matter--as described by quantum theory. Roger Penrose has proposed a new physics of objective reduction: "OR," which appeals to a form of quantum gravity to provide a useful description of fundamental processes at the quantum/classical borderline. Within the OR scheme, we consider that consciousness occurs if an appropriately organized system is able to develop and maintain quantum coherent superposition until a specific "objective" criterion (a threshold related to quantum gravity) is reached; the coherent system then self-reduces (objective reduction: OR). We contend that this type of objective self-collapse introduces non-computability, an essential feature of consciousness which distinguishes our minds from classical computers. Each OR is taken as an instantaneous event--the climax of a self-organizing process in fundamental spacetime--and a candidate for a conscious Whitehead "occasion of experience." How could an OR process occur in the brain, be coupled to neural activities, and account for other features of consciousness? We nominate a quantum computational OR process with the requisite characteristics to be occurring in cytoskeletal micro-tubules within the brain's neurons. In this model, quantum-superposed states develop in microtubule subunit proteins ("tubulins") within certain brain neurons, remain coherent, and recruit more superposed tubulins until a mass-time-energy threshold (related to quantum gravity) is reached. At that point, self-collapse, or objective reduction (OR), abruptly occurs. We equate the pre-reduction, coherent superposition ("quantum computing") phase with pre-conscious processes, and each instantaneous (and non-computable) OR, or self-collapse, with a discrete conscious event. Sequences of OR events give rise to a "stream" of consciousness. Microtubule-associated proteins can "tune" the quantum oscillations of the coherent superposed states; the OR is thus self-organized, or "orchestrated" ("Orch OR"). Each Orch OR event selects (non-computably) microtubule subunit states which regulate synaptic/neural functions using classical signaling. The quantum gravity threshold for self-collapse is relevant to consciousness, according to our arguments, because macroscopic superposed quantum states each have their own spacetime geometries. These geometries are also superposed, and in some way "separated," but when sufficiently separated, the superposition of spacetime geometries becomes significantly unstable and reduces to a single universe state. Quantum gravity determines the limits of the instability; we contend that the actual choice of state made by Nature is non-computable. Thus each Orch OR event is a self-selection of spacetime geometry, coupled to the brain through microtubules and other biomolecules. If conscious experience is intimately connected with the very physics underlying spacetime structure, then Orch OR in microtubules indeed provides us with a completely new and uniquely promising perspective on the difficult problems of consciousness.

Brain↗
PubMed2002

Pathophysiology of altered consciousness during seizures: Subtraction SPECT study.

BACKGROUND: The mechanisms underlying altered consciousness during seizures are poorly understood. Previous clinicopathologic studies suggest a role for the thalamus and upper brainstem in consciousness mechanisms. OBJECTIVE: To examine blood flow changes associated with altered consciousness during seizures. METHODS: Seventy-one patients with epilepsy who underwent video-EEG monitoring and ictal/interictal SPECT were studied. Patients were divided into three groups depending on their conscious state during seizures: 1) complete impairment of consciousness (CI), 2) no impairment of consciousness (NI), or 3) uncertain impairment of consciousness (UI). The distribution of blood flow changes during these seizures was assessed by subtraction (ictal - interictal) SPECT co-registered to MRI. Conscious state was assessed in relation to secondary ictal hyperperfusion in subcortical regions (i.e., thalamus and upper brainstem). RESULTS: Impairment of consciousness showed a strong association with secondary hyperperfusion in the thalamic/upper brainstem region (p = 0.01), occurring in 92% (45/49) of CI, 69% (9/13) of UI, and 11% (1/9) of NI. CONCLUSIONS: These findings are consistent with a role for the thalamus and upper brainstem in consciousness mechanisms. The authors suggest that the spread of epileptic discharges or a trans-synaptic activation (diaschisis) of these structures is an important mechanism in the alteration of consciousness during seizures. Variance in the results may be due to differences in timing of radioisotope injection, sensitivity of the subtraction SPECT technique, and the ability to clinically assess the conscious state.

Adolescent↗
PubMed2001

The sense of consciousness.

I propose that consciousness might be understood as the property of a system that functions as a sense in the biological meaning of that term. The theory assumes that, as a complex system, the sense of consciousness is not a fixed structure but implies structure with variations and that it evolved, as many new functions do, through the integration of simpler systems. The recognized exteroceptive and enteroceptive senses provide information about the organism's environment and about the organism itself that are important to adaptation. The sense of consciousness provides information about the brain and thus about the organism and its environment. It senses other senses and processes in the brain, selecting and relating components into a form that "makes sense"-where making sense is defined as being useful to the organism in its adaptation to the environment. The theory argues that this highly adaptive organizing function evolved with the growing complexity of the brain and that it might have helped resolve discrepancies created at earlier stages. Neural energies in the brain that are the input to the sense of consciousness, along with the processing subsystem of which they are a part, constitute the base of consciousness. Consciousness itself is an emergent effect of an organizing process achieved through the sense of consciousness. The sense of consciousness thus serves an organizing function although it is not the only means of organization in the brain. Its uniqueness lies in the character of the organization it creates with consciousness as a property of that organization. The paper relates the theory to several general conceptions-interactionism, epiphenomenalism and identity theory-and illustrates a number of testable hypotheses. Viewing consciousness as a property of a sense provides a degree of conceptual integration. Much of what we know about the evolution and role of the conventionally recognized senses should help us understand the evolution and role of the sense of consciousness, and of consciousness itself.

Behavior↗
PubMed2002

Evaluation of endoscopic retrograde cholangiopancreatography under conscious sedation and general anesthesia.

BACKGROUND AND STUDY AIMS: In adults, general anesthesia is usually only provided during endoscopic retrograde cholangiopancreatography (ERCP) when prior attempts using conscious sedation have failed. It was hypothesized that in our hospital, other factors might be associated with general anesthesia for ERCP. The aim of this study was therefore to assess the indications for ERCP under general anesthesia, and to evaluate the underlying diseases, type, and efficacy of ERCP under general anesthesia in comparison with conscious sedation. PATIENTS AND METHODS: We retrospectively analyzed 1,056 ERCPs that had been carried out with the patients under general anesthesia or conscious sedation. The indications for general anesthesia were recorded, and the underlying diseases, the type and success of the interventions, and the causes of premature ERCP termination in both groups were assessed. RESULTS: Eighteen percent of the ERCPs were performed under general anesthesia and 82% under conscious sedation. The indications for general anesthesia were related to the type of procedure planned (46%), premature termination of ERCP under conscious sedation (28%), and other reasons. Patients with primary sclerosing cholangitis and liver transplant recipients received general anesthesia more frequently (general anesthesia vs. conscious sedation, 36% vs. 16%, P < 0.0001 and 22% vs. 13%, P = 0.003). Conscious sedation was provided more frequently in patients with neoplasms and cholelithiasis (21% vs. 12%, P = 0.004 and 13% vs. 3%, P < 0.001). Painful dilations were performed more frequently with the patients under general anesthesia (60% vs. 19%, P < 0.001), whereas major papillotomies were preferably performed with conscious sedation (34% vs. 21%, P = 0.006). More interventions per ERCP were performed with the patient under general anesthesia compared to conscious sedation (P < 0.001), during the same time (51 +/- 28 min vs. 52 +/- 26 min, P = 0.39). With conscious sedation, the ERCP failure rate was double that with general anesthesia (7% vs. 14%, P = 0.012), mainly due to inadequate conscious sedation (61%). CONCLUSIONS: The frequent use of general anesthesia for ERCP at our institution is related to the underlying diseases, which are frequently treated with complex and painful ERCP procedures. The efficacy of ERCP with general anesthesia supports a continued preference for general anesthesia rather than conscious sedation when complex and painful interventional ERCP procedures are planned.

Anesthesia, General↗
PubMed1998

How to study consciousness scientifically.

The neurosciences have advanced to the point that we can now treat consciousness as a scientific problem like any other. The problem is to explain how brain processes cause consciousness and how consciousness is realized in the brain. Progress is impeded by a number of philosophical mistakes, and the aim of this paper is to remove nine of those mistakes: (i) consciousness cannot be defined; (ii) consciousness is subjective but science is objective; (iii) brain processes cannot explain consciousness; (iv) the problem of 'qualia' should be set aside; (v) consciousness is epiphenomenal; (vi) consciousness has no evolutionary function; (vii) a causal account of consciousness is necessarily dualistic; (viii) science is reductionistic, so a scientific account of consciousness would show it reducible to something else; and (ix) an account of consciousness must be an information processing account.

Biological Evolution↗
PubMed2000

Consciousness.

Until recently, most neuroscientists did not regard consciousness as a suitable topic for scientific investigation. This reluctance was based on certain philosophical mistakes, primarily the mistake of supposing that the subjectivity of consciousness made it beyond the reach of an objective science. Once we see that consciousness is a biological phenomenon like any other, then it can be investigated neurobiologically. Consciousness is entirely caused by neurobiological processes and is realized in brain structures. The essential trait of consciousness that we need to explain is unified qualitative subjectivity. Consciousness thus differs from other biological phenomena in that it has a subjective or first-person ontology, but this subjective ontology does not prevent us from having an epistemically objective science of consciousness. We need to overcome the philosophical tradition that treats the mental and the physical as two distinct metaphysical realms. Two common approaches to consciousness are those that adopt the building block model, according to which any conscious field is made of its various parts, and the unified field model, according to which we should try to explain the unified character of subjective states of consciousness. These two approaches are discussed and reasons are given for preferring the unified field theory to the building block model. Some relevant research on consciousness involves the subjects of blindsight, the split-brain experiments, binocular rivalry, and gestalt switching.

Animals↗
PubMed1993

Spatial attention and two modes of visual consciousness.

The relationship between spatial attention and visual consciousness was critically examined in an attempt to show the operation of two simultaneously available modes of visual consciousness (i.e., object consciousness, which concerns the conscious identification of objects, and background consciousness, which deals with conscious monitoring of the background scene). The traditional view seems to pay attention only to object consciousness, which is a product of spatial attention. To substantiate the hypothesis, five topics from varied fields of human experimental psychology were chosen: iconic storage, stabilized retinal image disappearance, stable perception of external space, texture segregation and attention, and spatial frequency sensitivity in a figure-ground reversal figure. The findings of these studies suggest that there may be visual consciousness outside of focal attention and that background consciousness operates as a default mode for global scene analysis and early warning of anomalies. Finally, neural substrata for these two modes of consciousness are suggested.

Attention↗
PubMed1995

Visual perception and phenomenal consciousness.

In the (re-)animated debate on consciousness we focus on three questions: Who has consciousness? What is its neuronal basis? What is its function? Regarding the first, we suggest that consciousness is exclusive to living organisms able to distinguish self from non-self. It may be restricted further to organisms who possess a repertoire of overt and covert behaviour which can be voluntarily modified and suppressed. This requires an intermediary neuronal net mediating between sensory input and behavioural output. What are the properties of this net which distinguish unalloyed information processing per se from conscious representation? To tackle this second question, we use the visual system and the functional losses that result from lesions at its different levels, and differentiate a reflexive, a phenomenal, and a consciously accessible stage of visual processing. We suggest that the latter two represent two distinct aspects of consciousness. Blindsight, a neurological example of visual processing in the absence of phenomenal vision, could help to elucidate the neuronal basis of phenomenality, and the special role of striate cortex. Like the patients, our monkeys with unilateral striate cortical removal show evidence not just of residual visual processing, but of the same absence of phenomenal vision, opening routes to further exploring the details of its neuronal implementation. The second aspect, conscious access to presently or previously processed information, is likely to require higher cortical structures, and may depend on the stage of phenomenal representations. In patients with blindsight, both aspects are lost, and it is conceivable that a loss of phenomenality generally causes a loss of conscious accessibility. One important function of phenomenal representations, our third question, would then be to allow conscious retrieval and manipulation of currently processed or formerly stored information, enabling organisms to consciously think and plan.

Animals↗
PubMed2001

Towards a cognitive neuroscience of consciousness: basic evidence and a workspace framework.

This introductory chapter attempts to clarify the philosophical, empirical, and theoretical bases on which a cognitive neuroscience approach to consciousness can be founded. We isolate three major empirical observations that any theory of consciousness should incorporate, namely (1) a considerable amount of processing is possible without consciousness, (2) attention is a prerequisite of consciousness, and (3) consciousness is required for some specific cognitive tasks, including those that require durable information maintenance, novel combinations of operations, or the spontaneous generation of intentional behavior. We then propose a theoretical framework that synthesizes those facts: the hypothesis of a global neuronal workspace. This framework postulates that, at any given time, many modular cerebral networks are active in parallel and process information in an unconscious manner. An information becomes conscious, however, if the neural population that represents it is mobilized by top-down attentional amplification into a brain-scale state of coherent activity that involves many neurons distributed throughout the brain. The long-distance connectivity of these 'workspace neurons' can, when they are active for a minimal duration, make the information available to a variety of processes including perceptual categorization, long-term memorization, evaluation, and intentional action. We postulate that this global availability of information through the workspace is what we subjectively experience as a conscious state. A complete theory of consciousness should explain why some cognitive and cerebral representations can be permanently or temporarily inaccessible to consciousness, what is the range of possible conscious contents, how they map onto specific cerebral circuits, and whether a generic neuronal mechanism underlies all of them. We confront the workspace model with those issues and identify novel experimental predictions. Neurophysiological, anatomical, and brain-imaging data strongly argue for a major role of prefrontal cortex, anterior cingulate, and the areas that connect to them, in creating the postulated brain-scale workspace.

Brain↗