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PubMed2005

Detection of consciousness by electroencephalogram and auditory evoked potentials.

BACKGROUND: A set of electroencephalographic and auditory evoked potential (AEP) parameters should be identified that allows separation of consciousness from unconsciousness (reflected by responsiveness/unresponsiveness to command). METHODS: Forty unpremedicated patients received anesthesia with remifentanil and either sevoflurane or propofol. With remifentanil infusion (0.2 microg . kg . min), patients were asked every 30 s to squeeze the investigator's hand. Sevoflurane or propofol was given until loss of consciousness. After intubation, propofol or sevoflurane was stopped until patients followed the command (return of consciousness). Thereafter, propofol or sevoflurane was started again (loss of consciousness), and surgery was performed. Return of consciousness was observed after surgery. The electroencephalogram and AEP from immediately before and after the transitions were selected. Logistic regression was calculated to identify models for the separation between consciousness and unconsciousness. For the top 10 models, 1,000-fold cross-validation was performed. Backward variable selection was applied to identify a minimal model. Prediction probability was calculated. The digitized electroencephalogram was replayed, and the Bispectral Index was measured and accordingly analyzed. RESULTS: The best full model (prediction probability 0.89) contained 15 AEP and 4 electroencephalographic parameters. The best minimal model (prediction probability 0.87) contained 2 AEP and 2 electroencephalographic parameters (median frequency of the amplitude spectrum from 8-30 Hz and approximate entropy). The prediction probability of the Bispectral Index was 0.737. CONCLUSIONS: A combination of electroencephalographic and AEP parameters can be used to differentiate between consciousness and unconsciousness even in a very challenging data set. The minimal model contains a combination of AEP and electroencephalographic parameters and has a higher prediction probability than Bispectral Index for the separation between consciousness and unconsciousness.

Adult↗
PubMed2006

S100B protein in conscious carbon monoxide-poisoned rats treated with normobaric or hyperbaric oxygen.

OBJECTIVE: To evaluate S100B, an astroglial structural protein, during normobaric and hyperbaric oxygen therapy of conscious carbon monoxide (CO)-poisoned rats. So far, the usefulness of hyperbaric oxygen therapy in conscious CO-poisoned patients has been shown with neuropsychological testing. The S100B protein has been demonstrated as a possible biochemical marker and prognostic parameter in CO-poisoned rats. DESIGN: Randomized, controlled interventional trial. SETTING: University laboratory. SUBJECTS: : Male Wistar rats weighing 254 +/- 14 g. INTERVENTIONS: The rats were exposed to a mixture of 3,000 ppm CO in air for 60 mins. After CO exposure, the first group of eight conscious rats was exposed to ambient air for 30 mins, the second group of six conscious rats was exposed to 100% normobaric oxygen for 30 mins, and the third group of six conscious rats was exposed to 100% hyperbaric oxygen at 3 bars for 30 mins. Blood samples were taken from the jugular vein just before CO exposure and immediately after oxygen therapy. The level of consciousness was evaluated at the end of exposure, and the survival rate was monitored for 14 days. The S100B concentrations were measured with a commercial immunoluminometric assay. MEASUREMENTS AND MAIN RESULTS: Analyses of differences in S100B levels between different kinds of therapy before and after treatment showed a global significant difference (p = .002). The post hoc test results showed that S100B levels after therapy of the first group treated with ambient air (0.16 +/- 0.07 microg/L) and the second group treated with normobaric oxygen (0.19 +/- 0.05 microg/L) were similar (p = .741), and both of them were significantly different, with much higher values of S100B levels after therapy, from the third group treated with hyperbaric oxygen (0.06 +/- 0.03 microg/L; p = .018 and p = .002, respectively). All the rats survived. CONCLUSIONS: S100B is elevated in conscious CO-poisoned rats left on ambient air or treated with normobaric oxygen, but not in conscious CO-poisoned rats treated with hyperbaric oxygen.

Animals↗
PubMed1986

Consciousness as a neurological concept in epileptology: a critical review.

This essay explores the usefulness of the concept of consciousness in epileptology and concludes that it does not further the understanding of seizure mechanisms and brain function. The reasons for this are both theoretical and empirical. Consciousness cannot be adequately defined. This may explain why attempts at accounting for it in neurobiological terms have failed. Epistemological and scientific arguments are reviewed which suggest why a satisfactory explanation of consciousness is not now and may never be possible. There are, however, aspects of conscious experience such as perception, cognition, memory, affect, and voluntary motility that are open to neurobiological research. Careful observations of epileptic seizures with "loss of consciousness" often reveal that only some components of consciousness are impaired. "Loss of consciousness" during a seizure, often presenting as unresponsiveness, may be due to aphasia, inability to perform voluntary movements, ictal or postictal amnesia (sometimes with preservation of memory during the ictus itself), or to diversion of attention by a hallucinated experience. A plea is made to observe accurately and interact with the patient during an attack in order to distinguish between these various behavioral disturbances masquerading as "loss of consciousness."

Adult↗
PubMed1999

Consciousness as a definition of death: its appeal and complexity.

A new formulation of death proposed in this study is based on the basic physiopathological mechanisms of consciousness generation in human beings. Two physiological components control conscious behavior: arousal and awareness (content of consciousness). We cannot simply differentiate and locate arousal as a function of the ascending reticular activating system and awareness as a function of the cerebral cortex. Substantial interconnections among the brainstem, subcortical structures and the neocortex, are essential for subserving and integrating both components of human consciousness. Therefore, consciousness does not bear a simple one-to-one relationship with higher or lower brain structures, because the physical substratum for consciousness is based on anatomy and physiology throughout the brain. This new account of human death is based on the irreversible loss of consciousness because it provides the key human attributes and the highest level of control in the hierarchy of integrating functions within the organism. The notion of consciousness as the ultimate integrative function is more consistent with the biologically-based systems than the more philosophically-based notions of personhood.

Arousal↗
PubMedDate not supplied

[Towards a taxonomy of consciousness].

INTRODUCTION: There are many definitions in order to describe the consciousness. In the literature appear concepts such alertness, attention, knowledge, conscious experience, awareness of deficits, self awareness, theory of mind in relation with consciousness definition. This multiplicity conceptual lead to formulate a question: Do exist different levels of complexity in the consciousness that depend on neuroanatomics structures differentiated? METHOD: In this paper an approximation toward a taxonomy of consciousness is offered and five levels of complexity and its relation with cerebral structures differentiated are suggested. In the first place, it s consider the alertness state as a necessary condition to exist the consciousness and his relation with attentional states. In the second place, it s present the conscious experience that depends on synchronicity neural activity. On the other hand, the daily clinic work shows the possibility of the existence of a consciousness for each specific field of knowledge. In the fourth place, it s located the self awareness understood like the capacity to perceive to us with objectivity but maintaining a subjectivity sense. At last, the theory of mind refers to the ability for attribute to the others specific mental states. CONCLUSION: It s plan an analysis of the different models that have tried to give an answer to each one of complexity levels to attempt an approach based on the analytic science and not descriptive plane.

Attention↗
PubMedDate not supplied

[Consciousness].

"Consciousness" is the feeling that each individual has of his own existence (self-awareness) and also the state which permits him to perceive his environment (consciousness and wakefulness). These two types of consciousness, apparently quite different, are in fact the two converging stems of the perceptions that the nervous system provides to the organism. To explain this better, it is necessary to refer to the evolution of the nervous system organization among the species and to imagine what perception the nervous system provides at each stage of this evolution, or in each species harbouring a nervous system corresponding to a given stage. At the beginning, the role of the nervous system is to protect the organism and only by an automatic and reflex organization. It corresponds to an unconscious alertness which permits to perceive the environment; it is the prefiguration of the future consciousness. Self-awareness seems to appear with the centrencephalic and limbic structures which are the highest part of the nervous system in the inferior mammals and the central part in man. At this stage, acquisition memory and affectivity with its different manifestations (emotions, mood, pain...) are established. This kind of consciousness is difficult to imagine since it is only sensorial and affective. Mental consciousness appears with the mental activity in the cerebral hemispheres. It is more than likely that it exists in the superior mammals though it is impossible to imagine what it corresponds to. It reaches the highest development in the man in whose the frontal lobes have the largest extent. Speech is the most striking figure of this development. At each stage of the evolution, consciousness expresses the nervous system activity, centered on a perception, the level of which corresponds to the improvements occurring at each stage and superadded to the previous ones. Hence it is obvious that consciousness has no specific center or pathway. It relies upon structures that participate in triggering and regulating the nervous activity and that utilize the particular centers of perception and analysis. These structures are: the reticular formation and the diffuse thalamic system.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

Conscious sedation for dentistry: risk management and patient selection.

There are many safe and effective medications available to the dental practitioner for producing conscious sedation. Given the many sedatives available, all possessing slightly different clinical characteristics and various degrees of risk, careful consideration needs to be given to the objectives of the sedation when deciding which pharmacologic agents to use. Before making plans to sedate dental patients, however, one needs to make sure that several "layers" of risk management are in place to ensure the sedation procedure is as safe as possible. Included in this risk management plan is a complete understanding of the regulations that define conscious sedation and the training that is required to deliver this state of depressed consciousness. Careful attention also needs to be given to selecting appropriate dental patients for sedation. A thorough understanding of the patient's physical and psychologic status is necessary when making decisions about sedation. Because most dental disease is not life threatening, dental treatment needs tend to be primarily elective in nature. Considering the training requirements for delivering inhalational or enteral conscious sedation with a single agent, it is prudent to limit this type of sedation to the patient population that is healthy (e.g., ASA I and II) and psychologically stable as a way of minimizing risk. The amount of additional risk one encounters when sedating more medically compromised patients (ASA III and greater) should suggest that deferring elective dental treatments until the health status improves is prudent. In situations in which an improvement in the patient's health status is not likely, referral to someone with more experience sedating medically compromised patients is strongly recommended. Equally important to the conscious sedation risk management plan is an assurance that the patient understands what is meant by conscious sedation and that their treatment expectations are realistic. Finally, even though conscious sedation is safe when all precautions are followed, being prepared to manage unexpected sedation-related emergencies is necessary. The principles of risk management covered in this article are applicable to other articles in this issue, in which N2O/O2 inhalational sedation and enteral sedation in adults and children are discussed. The remaining article in this section that reviews the prevention of medical emergencies and the pharmacologic agents necessary to treat emergency events that are likely to occur in dental settings further enhances the level of preparedness necessary when administering conscious sedation to adults and children.

Administration, Inhalation↗
PubMed2003

Medical aspects of the minimally conscious state in children.

The minimally conscious state is a condition of severely altered consciousness in which minimal but definite behavioral evidence of self or environmental awareness is demonstrated. This must be established on a reproducible or sustained basis by one or more of four types of behaviors including simple command-following, gestural or verbal 'yes/no' responses, intelligible verbalizations, or purposeful behaviors. The minimally conscious state can occur in children and usually is due to acquired brain injuries (traumatic and non-traumatic), central nervous system degenerative and neurometabolic disorders or congenital or developmental disorders. It is assumed that the lower limit of the minimally conscious state occurs when patients emerge from a vegetative state. What remains uncertain is how we can assess the upper limits, that is the degree of improvement that indicates that an individual is no longer minimally conscious. It also is unknown if, when and to what extent children can emerge from a minimally conscious state and whether their prognosis is better than children who are vegetative. It is assumed that the minimally conscious state may become 'permanent' 12 months after traumatic brain injury and 3 months after non-traumatic injury although there have been no studies that have examined this issue. Medical and rehabilitative treatment of children in a minimally conscious state should be provided to maintain comfort, reduce complications, and optimize functional recovery.

Adolescent↗
PubMed1992

Effects of self-consciousness and social anxiety on self-disclosure among unacquainted individuals: an application of the social relations model.

Recent research has demonstrated a positive relationship between private self-consciousness and the tendency to self-disclose. These studies have relied exclusively upon self-reports of disclosure. In the present study, Kenny's Social Relations Model (Kenny & La Voie, 1984) was employed to examine the relationship between a subject's self-reports and others' reports of a subject's level of self-disclosure and the relationship of these reports to private self-consciousness, as well as the other traits measured by the self-consciousness scale: public self-consciousness and social anxiety. Unacquainted college women (N = 102) participated in one-on-one interactions in a round-robin design. Subject's self-reports of disclosure and their levels of private self-consciousness correlated positively. The partners' reports of an individual's disclosure, however, were not related to the individual's level of private self-consciousness. The discrepancy between these correlations emphasizes the necessity to ground research in personal relationships on interacting pairs and not only on the self-reports of one member. Future research that would explore this difference is discussed. The examination of the self- and partner reports and subjects' levels of public self-consciousness and social anxiety demonstrated that these two traits significantly influence the acquaintance process. Public self-consciousness related positively to subjects' beliefs that they had created consistent impressions upon their partners. Social anxiety correlated negatively with partners' reports of a subject's dyadic involvement and openness.

Adult↗
PubMed1997

[Use of the Glasgow Coma Scale and the Jouvet Coma Scale to evaluate the level of consciousness].

The Glasgow Coma Scale (GCS) and the Jouvet Coma Scale (JCS) have been evolved for assessing the depth and duration of impaired consciousness and coma. The analysis and the utilization of these scales have showed that they are complementary. The GCS is more sensitive when there is a more intense loss of consciousness, whereas the JCS shows its sensitivity better in the states close to normal. This study was aimed to compare the results obtained from the evaluation of the consciousness level by the utilization of the two scales. The comparison was done within a prospective study with 48 patients, all of them over 18 years old, interned in three intensive care units of different hospitals in the city of São Paulo. The evaluations were done daily by the researchers and the scales applied in sequence totaling 5 minutes. Each scale was applied in 106 evaluations, and the results showed a statistically meaningful difference between the GCS and the JCS as to the indication of alteration in the consciousness levels. In 37.74% of the evaluations done with the JCS there was an indication of alteration in the consciousness level, whereas with the GCS the alteration was present in only 23.58% of the evaluations. Another important observation about the utilization of both scales was that people whose scores were between 9 and 10 in the GCS had had an stronger indication of alteration of consciousness level by the same scale, while those with scores between 12 and 15 had a stronger indication of alteration in the consciousness level by JCS. When using GCS there has been the application of the non-testable (NT) in 20% of the evaluations. This did not occur when using the JCS. However it is believed that specific conditions of that particular group might have led to that result as well as specific characteristics of groups of patients might favor the utilization of different scales to evaluate the consciousness level. Therefore the final choice between such scales should consider the conditions and the peculiar characteristics of the clientele to be evaluated and not individual or health department services preferences.

Adolescent↗
PubMed1992

Aggression, alcohol dependency, and self-consciousness among high school students of divorced and nondivorced parents.

134 high school students from a small high school in north central Kansas completed the MacAndrew Alcoholism Scale, Fenigstein, et al.'s Self-consciousness Scale, and Zaks' Aggression Scale. Analyses of variance showed significant differences between boys and girls but not among grades. On the aggression and alcohol measures boys scored higher than girls, but lower on public self-consciousness. Youth of divorced parents scored significantly higher than those of nondivorced parents on aggression, private self-consciousness, and general self-consciousness. Aggression scores were significantly and positively correlated with those on the alcohol and private self-consciousness scales. When students' alcoholism scores indicate problems with alcohol, their scores on aggression indicate greater aggression and their private self-consciousness scores indicate sensitivity toward events in their environment, then having concerns about inner self can inhibit the action required for change. MacAndrew scores correlated significantly and negatively with scores on social anxiety about self-consciousness. When MacAndrew scores indicated problems with alcohol, the students' scores on social anxiety about self-consciousness suggested confidence in social settings, being at ease interacting with people. The present study involved students from a single rural district so increased understanding will require more extensive research if strategies for prevention and intervention are to be developed and utilized.

Adolescent↗
PubMed1993

Slippage in the unity of consciousness.

Many psychological studies assume a unity of consciousness. Doubt is cast on this assumption (a) by psychophysical studies in normal subjects and those with blindsight showing the simultaneous dissociation of different modes of report of a sensation, and (b) by clinical studies of anosognosic patients showing dissociations of awareness of their own states. These and other phenomena are interpreted to imply two kinds of division of consciousness: the separation of phenomenal experience from reflexive consciousness and the non-unity of reflexive consciousness. Reflexive consciousness is taken to be necessary for report and is associated with the self as the subject of experience and agent of report. Reflexive consciousness is operative only when we attend to our own states. When we are involved in the world reflexivity intervenes less and our consciousness is more unified.

Awareness↗
PubMed1979

The tasks of consciousness: how could the brain do them?

According to Darwin's theory of evolution by natural selection, the existence of mental operations proves their usefulness. Darwin called himself a mental materialist. This is one scientific theory of consciousness. Human consciousness has three useful aspects: awareness, intentionality and sharing with others. All have simple equivalents in animals. The latter two are neglected in neurophysiology and experimental psychology. Developmental, neuroanatomical and neuropsychological evidence shows that the human brain has innate structures of awareness, intentionality and interpersonal sharing. Human life depends on interpersonal cooperation. We may have a conscious self, but consciousness of others is essential in us. Studies of commissurotomy patients demonstrate the elaborate interconnected neural organization of consciousness and provide evidence of underlying and necessary levels of motivation, perception and motor integration below consciousness. Additionally, they show that awareness may be split into two different modes. These regulate one another during development and are complementary in culturally sophisticated adult life. One hemisphere, usually the left, has responsibility for expressing ideas and purposes in language. The other responds to the phenomenal context and the subjective situation. Both have human experiences and purposes. Both still collaborate in a unified intentional system after commissurotomy. Infant studies reveal that language develops out of an interpersonal mental process. This seems to control development of thinking. Thus notions of the newborn as an isolated amoral id, and of the infant as an egocentric discoverer of the object concept, must be rejected. Cultivation of moral awareness and a sense of purpose guided by meanings and values depends on innate organization of the human brain for interpersonal consciousness.

Awareness↗
PubMed1979

Neurophysiological mechanisms and consciousness.

Consciousness may be understood as a behavioural state and thus levels of consciousness may be distinguished. But consciousness as we understand it is an experience. Any critical reasoning about it will lead to a dualistic formula. A neurophysiological mechanism may exist for this. In the neocortex various aspects of the world and of the physical and social relationships of the individuum to the world are represented through thalamocortical projection systems. There is no unified representation of the world in any single cortical area. All neocortical outputs feed into action systems of the brain. The synthesis of the distributed cortical representations of the world is thus realized through the action elicited by their combination. The action systems of the midbrain-cerebellum and the basal ganglia feed back into neocortical areas (internal loops). The action itself changes the relationship of the individual to the outside world and thus its representation in the brain (external loops). The role of the basal ganglia in the normal functioning of processes in consciousness and in the synthesis of cortical representations is described, which further emphasizes the intricate connections between motor performance and consciousness. The function of the reticular substance and related structures is seen as a gating mechanism for the (thalmic) access gates to the cortex and thus to mechanisms of conscious experience. The basis for the experience of consciousness is the symbolic representation of the world and of the individual to that individual's brain. This self-representation is based on the linguistic competence of the brain in a broad sense and is therefore possible only for brains with such a competence. The symbolic self-representation is called the reflective loop and its conditons are briefly discussed.

Basal Ganglia↗
PubMed1998

The timing of conscious experience: a critical review and reinterpretation of Libet's research.

An extended examination of Libet's works led to a comprehensive reinterpretation of his results. According to this reinterpretation, the Minimum Train Duration of electrical brain stimulation should be considered as the time needed to create a brain stimulus efficient for producing conscious sensation and not as a basis for inferring the latency for conscious sensation of peripheral origin. Latency for conscious sensation with brain stimulation may occur after the Minimum Train Duration. Backward masking with cortical stimuli suggests a 125-300 ms minimum value for the latency for conscious sensation of threshold skin stimuli. Backward enhancement is not suitable for inferring this latency. For determining temporal relations between stimuli that correspond to subjects' reports, the end of cerebral Minimum Train Duration should be used as reference, rather than its onset. Results of coupling peripheral and cortical stimuli are explained by a latency after the cortical Minimum Train Duration, having roughly the same duration as the latency for supraliminal skin stimuli. Results of coupling peripheral stimuli and stimuli to medial lemniscus (LM) are explained by a shorter LM latency and/or a longer peripheral latency. This interpretation suggests a 230 ms minimum value for the latency for conscious sensation of somatosensory near-threshold stimuli. The backward referral hypothesis, as formulated by Libet, should not be retained. Long readiness potentials preceding spontaneous conscious or nonconscious movements suggest that both kinds of movement are nonconsciously initiated. The validity of Libet's measures of W and M moments (Libet et al., 1983a) is questionable due to problems involving latencies, training, and introspective distinction of W and M. Veto of intended actions may be initially nonconscious but dependent on conscious awareness.

Brain↗
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↗