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PubMed1994

EEG detection of nontonic-clonic status epilepticus in patients with altered consciousness.

Subtypes of status epilepticus (SE) without tonic-clonic convulsions (nontonic-clonic SE) present as altered consciousness sometimes with subtle motor activity and are important to consider in the differential diagnosis of patients with unexplained altered consciousness. Other patients may have altered consciousness with intermittent ictal activity on electroencephalography (EEG) that represents probable SE, but have other medical conditions that may be contributing to altered consciousness. EEG is the only reliable way to make the diagnosis of nontonic-clonic SE and we make emergency EEG available on a 24-h basis at our hospital. To determine how often definite or probable nontonic-clonic SE was detected by EEG we prospectively collected data on all cases where physicians ordered EEG to evaluate altered consciousness or possible SE. Out of 198 cases with altered consciousness but no clinical convulsions, 74 (37%) showed EEG and clinical evidence of definite or probable nontonic-clonic SE. Forty-two episodes (57%) were probable or definite complex partial SE, 29 (39%) were probable or definite subtle generalized SE, and three (4%) were myoclonic SE. In 23 SE cases altered consciousness was the only clinical sign at the time of diagnosis; subtle motor activity was present in 36 others. Neither clinical signs nor prior history predicted which patients showed SE on EEG. Nontonic-clonic SE followed a cerebral infarction in 16 cases. Contrary to other reports, we found no relationship between duration of SE and EEG pattern. Subtle generalized SE occurred most commonly in the setting of a diffuse brain injury rather than evolving from convulsive SE. This study demonstrates that nontonic-clonic SE is a common finding in patients with unexplained altered consciousness and EEG is necessary in the evaluation of these patients.

Adolescent↗
PubMed2005

Single-neuron theory of consciousness.

By most accounts, the mind arises from the integrated activity of large populations of neurons distributed across multiple brain regions. A contrasting model is presented in the present paper that places the mind/brain interface not at the whole brain level but at the level of single neurons. Specifically, it is proposed that each neuron in the nervous system is independently conscious, with conscious content corresponding to the spatial pattern of a portion of that neuron's dendritic electrical activity. For most neurons, such as those in the hypothalamus or posterior sensory cortices, the conscious activity would be assumed to be simple and unable to directly affect the organism's macroscopic conscious behavior. For a subpopulation of layer 5 pyramidal neurons in the lateral prefrontal cortices, however, an arrangement is proposed to be present such that, at any given moment: (i) the spatial pattern of electrical activity in a portion of the dendritic tree of each neuron in the subpopulation individually manifests a complexity and diversity sufficient to account for the complexity and diversity of conscious experience; (ii) the dendritic trees of the neurons in the subpopulation all contain similar spatial electrical patterns; (iii) the spatial electrical pattern in the dendritic tree of each neuron interacts non-linearly with the remaining ambient dendritic electrical activity to determine the neuron's overall axonal response; (iv) the dendritic spatial pattern is reexpressed at the population level by the spatial pattern exhibited by a synchronously firing subgroup of the conscious neurons, thereby providing a mechanism by which conscious activity at the neuronal level can influence overall behavior. The resulting scheme is one in which conscious behavior appears to be the product of a single macroscopic mind, but is actually the integrated output of a chorus of minds, each associated with a different neuron.

Animals↗
PubMed2006

Conscious, preconscious, and subliminal processing: a testable taxonomy.

Of the many brain events evoked by a visual stimulus, which are specifically associated with conscious perception, and which merely reflect non-conscious processing? Several recent neuroimaging studies have contrasted conscious and non-conscious visual processing, but their results appear inconsistent. Some support a correlation of conscious perception with early occipital events, others with late parieto-frontal activity. Here we attempt to make sense of these dissenting results. On the basis of the global neuronal workspace hypothesis, we propose a taxonomy that distinguishes between vigilance and access to conscious report, as well as between subliminal, preconscious and conscious processing. We suggest that these distinctions map onto different neural mechanisms, and that conscious perception is systematically associated with surges of parieto-frontal activity causing top-down amplification.

Brain↗
PubMed2005

A neuroscientific approach to consciousness.

For a neuroscientist, consciousness currently defies any formal operational definition. However, the phenomenon is distinct from self-consciousness: after all, one can "let oneself go," when experiencing extreme emotion, but still be accessing a sentiment, subjective, conscious state. This raw, basic subjective state does not appear to be an exclusive property of the human brain. There is no obvious qualitative transformation in either the anatomy or the physiology of the central nervous system of human or non-human animals, no phylogenetic Rubicon in the animal kingdom. Similarly, there is no clear ontogenetic line that is crossed as the brain grows in the womb, no single event or change in brain physiology, and certainly not at birth, when consciousness might be generated in an all-or-none fashion. A more plausible, and scientific, view of consciousness might be therefore that it is not a different property of the brain, some magic bullet, but that it is a consequence of a quantitative increase in the complexity of the human brain: consciousness will grow as brains grow. Hence, consciousness is most likely to be a continuously variable property of the brain, in both phylogenetic and ontogenetic terms. Here, we describe how modern techniques may be utilized to determine the physiological basis of consciousness.

Brain↗
PubMed2005

Consciousness and epilepsy: why are patients with absence seizures absent?

Epileptic seizures cause dynamic, reversible changes in brain function and are often associated with loss of consciousness. Of all seizure types, absence seizures lead to the most selective deficits in consciousness, with relatively little motor or other manifestations. Impaired consciousness in absence seizures is not monolithic, but varies in severity between patients and even between episodes in the same patient. In addition, some aspects of consciousness may be more severely involved than other aspects. The mechanisms for this variability are not known. Here we review the literature on human absence seizures and discuss a hypothesis for why effects on consciousness may be variable. Based on behavioral studies, electrophysiology, and recent neuroimaging and molecular investigations, we propose absence seizures impair focal, not generalized brain functions. Impaired consciousness in absence seizures may be caused by focal disruption of information processing in specific corticothalamic networks, while other networks are spared. Deficits in selective and varying cognitive functions may lead to impairment in different aspects of consciousness. Further investigations of the relationship between behavior and altered network function in absence seizures may improve our understanding of both normal and impaired consciousness.

Behavior↗
PubMed1997

Neurobiology of consciousness: an overview.

The aim of this review is to connect the phenomenology of consciousness to its neurobiology. A survey of the recent literature revealed the following points. (1) Comprehensive descriptions of consciousness, of its subjective as well as of its objective aspects, are both possible and necessary for its scientific study. An intentionality-modeling structure (an unified and stable ego refers to objects or to itself in the framework of a stable, reproducible, predictable world) accounts for the main features. (2) The material basis of consciousness can be clarified without recourse to new properties of matter or to quantum physics. Current neurobiology appears to be able to handle the problem. In fact, the neurobiology of consciousness is already in progress, and has achieved substantial results. At the system level, its main sources of data are: the neurophysiology of sleep-wakefulness, brain imaging of mental representations, attention and working memory, the neuropsychology of frontal syndrome, and awareness-unawareness dissociations in global amnesia and different forms of agnosia. At an intermediate level of organization, the mechanisms of consciousness may be the formation of a certain kind of neural assembly. (3) Further research may focus on neuropsychology and neurophysiology of object perception and recognition as a natural model of intentionality, perception of time, body schema, interhemispheric communications, 'voluntary' acts and mental images. The synthetic and dynamic views provided by brain imaging may be decisive for discovering the neural correlates of the integrative aspects of consciousness. (4) The neurobiological approach may, beyond the finding of cellular and molecular mechanisms, improve the general concepts of consciousness, overcome their antinomies and, against epiphenomenalism, definitely establish the reality of consciousness.

Animals↗
PubMed1992

[The concept of consciousness from the neuropsychiatric and interdisciplinary viewpoint].

In German neuropsychiatric literature there is an established tradition of viewing the disturbance of consciousness as a leading symptom of the acute, potentially reversible organic psychoses. Following the late H. H. Wieck acute organic psychoses which are characterized by a disturbance of wakefulness (syndromes of somnolence, sopor, coma), have to be distinguished from those with preserved wakefulness, which he called 'Durchgangssyndrom' (e.g. amnesic syndrome with affective lability). These two syndromes have found their way into textbooks and everyday language in medicine as 'disturbance of consciousness'. But neurology and psychiatry are developing in different directions. Furthermore classical phenomenological psychopathology is not a numerative science and consciousness is still under the persisting eliminative verdict of behaviorism. During the last decades consciousness and the psychopathology of acute organic psychoses have been subject to methodological reflection only with the aim of elaborating quantitative scales. In philosophy and psychology there has been a development towards a new impartiality about consciousness during the same time. The biological sciences have acquired more knowledge about cerebral functions with respect to conscious mental processes and between these sciences a fruitful cooperation has evolved from this. The different views of consciousness in relevant neighbouring sciences are looked at from two main points of view. Following classical descriptive tradition are: philosophy (Bunge, Seifert, Hastedt), philosophically oriented psychiatry (Jaspers, Ey), descriptive psychology (Deleay/Pichot), and the post-behaviorist psychology (Hilgard, Mandler, Natsoulas). On the other hand the neurobiologically oriented sciences: clinical neuropsychology (Mesulam, Kolb/Wishaw, Poeck, Stuss, Shallice), neurophysiology (Brain, Goldman-Rakic, Creutzfeldt, Roland), and neurophilosophy (Churchland, Oeser). These more recent developments can contribute to a more actual sight of psychopathology of consciousness in neurology and psychiatry.

Brain↗
PubMed1997

Disorders of consciousness: differential diagnosis and neuropathologic features.

Disorders of consciousness present intriguing challenges to the neurologist and neurorehabilitation specialist. Assessment is constrained by the lack of reliable methods of assessing consciousness, and there are no treatment interventions known to influence the course of recovery from these conditions. In addition, the relationship between the clinical features associated with these disorders and their corresponding pathophysiologic substrate is also unclear. Our understanding of disorders of consciousness has not kept pace with the advances in neurosurgical management that have decreased mortality following severe injury. There is still considerable confusion regarding differential diagnosis and prognostication concerning states of severely altered consciousness. The purpose of this article is to discuss the content and neural basis of consciousness and to review the terminology most often used to describe altered states of consciousness. The neurobehavioral criteria for differentiating among specific syndromes associated with severe alterations in consciousness are presented. Representative case studies are utilized to illustrate the characteristic clinical profiles of coma, vegetative state, persistent and permanent vegetative state, minimally conscious state, akinetic mutism, and locked-in syndrome. Areas of ambiguity and controversy are emphasized and future directions for research are suggested.

Akinetic Mutism↗
PubMed1997

Epilepsy and consciousness.

Seizure activity has long been associated with alterations in consciousness. Philosophical and neurologic debates concerning the definition of consciousness have led to confusion regarding an adequate third person assessment of a subjective experience. In order to avoid these controversies, neurologic evaluation of consciousness has focused on operational definitions that permit an objective assessment of behavioral responses that are constituent functions of consciousness. Clinical experience has demonstrated that ictal and post-ictal alterations in consciousness may be associated with loss of selected behavioral responses depending upon the focus and spread of seizure activity. Ictal electrophysiologic studies and brain stimulation has assisted in determining the anatomic structures involved in specific behavioral alterations. Consciousness-dependent mental activity can be modeled as a series of interactive parallel information channels that can be selectively disrupted at any stage of processing giving rise to ictal behavioral patterns. While such modeling falls to grasp the subjective nature of consciousness, it offers the clinical community an objective measure of those responses believed to be dependent on consciousness.

Brain↗
PubMed1999

Attention versus consciousness in the visual brain: differences in conception, phenomenology, behavior, neuroanatomy, and physiology.

A common confound between consciousness and attention makes it difficult to think clearly about recent advances in the understanding of the visual brain. Visual consciousness involves phenomenal experience of the visual world, but visual attention is more plausibly treated as a function that selects and maintains the selection of potential conscious contents, often unconsciously. In the same sense, eye movements select conscious visual events, which are not the same as conscious visual experience. According to common sense, visual experience is consciousness, and selective processes are labeled as attention. The distinction is reflected in very different behavioral measures and in very different brain anatomy and physiology. Visual consciousness tends to be associated with the "what" stream of visual feature neurons in the ventral temporal lobe. In contrast, attentional selection and maintenance are mediated by other brain regions, ranging from superior colliculi to thalamus, prefrontal cortex, and anterior cingulate. The author applied the common-sense distinction between attention and consciousness to the theoretical positions of M. I. Posner (1992, 1994) and D. LaBerge (1997, 1998) to show how it helps to clarify the evidence. He concluded that clarity of thought is served by calling a thing by its proper name.

Attention↗
PubMed2001

Is self-reflectiveness an unhealthy aspect of private self-consciousness?

A number of researchers (M. Conway & C. Giannopoulos, 1993; P. J. Watson & M. D. Biderman, 1993) have suggested that self-reflectiveness is an unhealthy aspect of private self-consciousness related to psychopathology. However, these studies did not control for the significant correlation that exists between self-reflectiveness and subscale factors of public self-consciousness: style consciousness and appearance consciousness. The purpose of this research was to address these interrelationships by comparing correlational results with those obtained from multiple regression analyses. Participants (N = 111) completed the Self-Consciousness Scale (A. Fenigstein, M. F. Scheier, & A. H. Buss, 1975) and the NEO-Five Factor Inventory (P. T. Costa & R. R. McCrae, 1992). The results suggested that when the effects of style consciousness and appearance consciousness are controlled, the relationship between self-reflectiveness and neuroticism is nonsignificant. Furthermore, multiple regression analyses suggested a significant relationship between self-reflectiveness and low levels of agreeableness. Aspects of self-consciousness may be better understood in the context of overlapping domains that consider both common and unique variance.

Adult↗
PubMed2002

The localizing value of ictal consciousness and its constituent functions: a video-EEG study in patients with focal epilepsy.

Using ictal neuropsychological testing in pre-surgical patients with focal epilepsies, we examined the localizing value of the constituent functions of consciousness as opposed to 'conscious behaviour' as a unitary variable. 'Conscious behaviour' was defined in terms of awareness and responsiveness. The constituent functions of consciousness examined included the orientation to the examiner, intentional behaviour demonstrated by expressive or receptive speech, and postictal memory. Frequency and patterns of impairment of constituent functions and 'conscious behaviour' were assessed. To achieve this, pre-surgical video-EEG (n = 40) or video-electrocorticography recordings (n = 76) of ictal neuropsychological assessments were reviewed retrospectively. Patients were divided into groups with frontal (n = 29), right temporal (n = 21), left temporal (n = 38) and bitemporal (n = 28) seizure activity. Consciousness was most commonly impaired in patients with bitemporal and left temporal seizure activity. There were different patterns of impairment of the assessed constituent functions in the four groups: patients with frontal seizure activity showed loss of orientation behaviour and expressive speech whereas patients with left temporal seizure activity had impairments of memory, expressive and receptive speech. Patients with seizure activity limited to the right temporal lobe rarely exhibited ictal impairment of any of the assessed functions. In contrast, patients with bitemporal seizure activity showed impairment of all examined functions. Hence, normal functioning of the left temporal lobe or both temporal lobes is necessary for the preservation of all constituent aspects of consciousness. The localizing value of patterns of impairment of constituent functions is superior to that of 'consciousness' as a whole.

Adolescent↗
PubMed2003

QT and RR intervals in conscious and anesthetized guinea pigs with highly varying RR intervals and given QTc-lengthening test articles.

A facile system for obtaining electrocardiograms from conscious animals was used to conduct studies on 12 animals studied both conscious and anesthetized, on 4 conscious animals given vehicle (0.5% methylcellulose) and QT-lengthening test articles, and on 6 animals given test articles thought to not lengthen QTc. In 12 animals whose ECGs were monitored via a bipolar transthoracic ECG, heart rates were slowed with 1.0 mg/kg zatebradine, while they were conscious in their slings, and after being anesthetized with ketamine/xylazine. The following regression equations were obtained relating QT to RR: QT = 44.7 ln RR - 132.9, r2 = 0.7, for conscious animals; QT = 79.4 ln RR - 287.4, r2 = 0.8 for anesthetized animals, with RR intervals varying between 150 and 550 ms. The anesthetic increases QT at all RR intervals (p < 0.001), but does not change the slope of the relationship between QT and RR when compared with the conscious guinea pig. The Fridericia method was best for correcting QT for RR interval in conscious guinea pigs, but the Bazett method was best for correcting in anesthetized animals. QTc lengthened significantly in all conscious guinea pigs given, orally, cisapride, ketoconazole, and sotalol (positive test articles) and did not change with methylcellulose (the vehicle) or with propranolol, verapamil, or enalapril (negative controls). These techniques and relationships demonstrate that this methodology may be useful in exploring torsadogenic effects of novel pharmacological entities.

Anesthesia↗
PubMed1997

Halothane and enflurane attenuate pulmonary vasodilation mediated by adenosine triphosphate-sensitive potassium channels compared to the conscious state.

BACKGROUND: Adenosine triphosphate (ATP)-sensitive potassium (k+ATP) channels play an important role in pulmonary vasoregulation. However, the effects of volatile anesthetics on k+ATP channel-mediated pulmonary vasoregulation have not been elucidated. The purpose of the present study was to investigate the effects of halothane and enflurane anesthesia on the pulmonary vasodilator response to the selective k+ATP channel agonist lemakalim (BRJ38227) compared with that measured in the conscious state. The authors also investigated the extent to which endogenous neurohumoral vasoconstrictor mechanisms modulate the vasodilator response to k+ATP channel activation. METHOD: Nineteen conditioned, male mongrel dogs were chronically instrumented to measure the left pulmonary vascular pressure-flow (LPQ) relationship. LPQ plots were generated by continuously measuring the pulmonary vascular pressure gradient (pulmonary arterial pressure-left atrial pressure) and left pulmonary blood flow during gradula (approximately 1 min) inflation of a hydraulic occluder implanted around the right main pulmonary artery. After preconstriction with the thromboxane analog, U46619 (9,11-dideoxy-11 alpha, 9 alpha-epoxymethano-prostaglandin F2 alpha), the pulmonary vascular dose-response relationship for the k+ATP agonist lemakalim was assessed in the conscious and halothane-anesthetized states and also in the conscious and enflurane-anesthetized states. This protocol was repeated in conscious and halothane-anesthetized dogs after combined neurohumoral block with antagonists of sympathetic alpha 1 adrenoreceptors, arginine vasopressin V1-receptors, and angiotensin II receptors. The effect of the k+ATP antagonist glybenclamide on the baseline LPQ relationship and on the lemakalim dose-response relationship also was assessed in conscious dogs. RESULTS: Compared with the conscious state, halothane, enflurane and glybenclamide had no net effect on the baseline LPQ relationship. In contrast, halothane and enflurane attenuated (P < 0.05) the pulmonary vasodilator response to lemakalim compared with the conscious state. Glybenclamide also caused a rightward shift (P < 0.05) in the lemakalim dose-response relationship. Combined neurohumoral block did not modulate the vasodilator response to lemakalim in the conscious state. The halothane-induced attenuation of the vasodilator response to lemakalim was apparent after combined neurohumoral block. CONCLUSION: These results indicate that halothane and enflurane act to reduce the magnitude of K+ATP channel-mediated pulmonary vasodilation. Reflex pulmonary vasoconstriction resulting from K+ATP mediated systematic hypotension does not alter the magnitude of the pulmonary vasodilator response to lemakalim nor is it responsible for the attenuated response to K+ATP channel activation during halothane anesthesia.

Adenosine Triphosphate↗
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↗
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↗