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Results for “CONSCIOUSNESS”

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At least 145 records · Page 8Linked to original sources

PubMed1996

Levels of consciousness and ventilatory parameters in young children during sedation with oral midazolam and nitrous oxide.

OBJECTIVE: To determine the ventilatory effects and levels of consciousness achieved during sedation with the combination of oral midazolam and inhaled nitrous oxide. DESIGN: Case series. SETTING: Surgical suite. PATIENTS: Twenty-two consecutive children, aged 1 to 3 years, were seen for elective, ambulatory surgery. INTERVENTIONS: Patients were premedicated with oral midazolam hydrochloride, 0.5 mg/kg, and then breathed 4 concentrations of nitrous oxide (N2O) in oxygen (15%, 30%, 45%, and 60%) for 4 minutes at each concentration prior to induction of general anesthesia. MAIN OUTCOME MEASURES: Levels of consciousness (conscious vs deep sedation) and ventilatory parameters: respiratory rate, end-tidal carbon dioxide tension (PETCO2), and oxyhemoglobin saturation (SPO2). Upper airway obstruction was diagnosed by clinical assessment by an experienced pediatric anesthesiologist (R.S.L.) and respiratory impedance plethysmography. RESULTS: During inhalation of N2O, 12 of the 20 children demonstrated a mild degree of ventilatory depression; PETCO2 values were equal to or greater than 45 mm Hg during at least 2 concentrations of N2O studied. There were no significant changes in SPO2 or PETCO2 with increasing concentrations of N2O (P > .05). Respiratory rates tended to be lower during inhalation of 15% N2O than at higher concentrations (P = .05). No child developed upper airway obstruction or hypoxemia (SPO2 < 92%) at any level of N2O inhalation. Sedation scores were significantly higher at 60% N2O than at all other concentrations of N2O (P < .02) At 15% N2O, 12 children were not clinically sedated, 8 children met the American Academy of Pediatrics definition of conscious sedation, and no child met the definition of deep sedation. At 30% N2O, 10 children were not clinically sedated, 9 met the definition of conscious sedation, and 1 child met the definition of deep sedation. At 45% N2O, 9 children were not clinically sedated, 9 met the definition of conscious sedation, and 2 met the definition of deep sedation. At 60% N2O, 6 children were not clinically sedated, 6 met the definition of conscious sedation, 6 met the definition of deep sedation, and 1 child progressed to a deeper level of sedation in that there was no response to a painful stimulus. One child was withdrawn from the study during inhalation of 45% N2O because of emesis. CONCLUSIONS: The combination of oral midazolam, 0.5 mg/kg, and up to 60% inhaled N2O caused mild ventilatory depression in some children and resulted in a progression from conscious to deep sedation beginning at 30% N2O. When using this particular combination of sedatives, practitioners should monitor each child's mental status continuously and adhere to the appropriate published guidelines for the monitoring and management of such patients.

Ambulatory Surgical Procedures↗

PubMed2005

Evolution of the neural basis of consciousness: a bird-mammal comparison.

The main objective of this essay is to validate some of the principal, currently competing, mammalian consciousness-brain theories by comparing these theories with data on both cognitive abilities and brain organization in birds. Our argument is that, given that multiple complex cognitive functions are correlated with presumed consciousness in mammals, this correlation holds for birds as well. Thus, the neuroanatomical features of the forebrain common to both birds and mammals may be those that are crucial to the generation of both complex cognition and consciousness. The general conclusion is that most of the consciousness-brain theories appear to be valid for the avian brain. Even though some specific homologies are unresolved, most of the critical structures presumed necessary for consciousness in mammalian brains have clear homologues in avian brains. Furthermore, considering the fact that the reptile-bird brain transition shows more structural continuity than the stem amniote-mammalian transition, the line drawn at the origin of mammals for consciousness by several of the theorists seems questionable. An equally important point is that consciousness cannot be ruled out in the absence of complex cognition; it may in fact be the case that consciousness is a necessary prerequisite for complex cognition.

Animals↗

PubMed1998

Neuronal phenomena associated with vigilance and consciousness: from cellular mechanisms to electroencephalographic patterns.

The neuroanatomical substrates controlling and regulating sleeping and waking, and thus consciousness, are located in the brain stem. Most crucial for bringing the brain into a state conducive for consciousness and information processing is the mesencephalic part of the brain stem. This part controls the state of waking, which is generally associated with a high degree of consciousness. Wakefulness is accompanied by a low-amplitude, high-frequency electroencephalogram, due to the fact that thalamocortical neurons fire in a state of tonic depolarization. Information can easily pass the low-level threshold of these neurons, leading to a high transfer ratio. The complexity of the electroencephalogram during conscious waking is high, as expressed in a high correlation dimension. Accordingly, the level of information processing is high. Spindles, and alpha waves in humans, mark the transition from wakefulness to sleep. These phenomena are related to drowsiness, associated with a reduction in consciousness. Drowsiness occurs when cells undergo moderate hyperpolarizations. Increased inhibitions result in a reduction of afferent information, with a lowered transfer ratio. Information processing subsides, which is also expressed in a diminished correlation dimension. Consciousness is further decreased at the onset of slow wave sleep. This sleep is controlled by the medullar reticular formation and is characterized by a high-voltage, low-frequency electroencephalogram. Slow wave sleep becomes manifest when neurons undergo a further hyperpolarization. Inhibitory activities are so strong that the transfer ratio further drops, as does the correlation dimension. Thus, sensory information is largely blocked and information processing is on a low level. Finally, rapid eye movement sleep is regulated by the pontine reticular formation and is associated with a "wake-like" electroencephalographic pattern. Just as during wakefulness, this is the expression of a depolarization of thalamocortical neurons. The transfer ratio of rapid eye movement sleep has not yet been determined, but seems to vary. Evidence exists that this type of sleep, associated with dreaming, with some kind of perception and consciousness, is involved in processing of "internal" information. In line with this, rapid eye movement sleep has higher correlation dimensions than slow-wave sleep and sometimes even higher than wakefulness. It is assumed that the "near-the-threshold" depolarized state of neurons in the thalamus and cerebral cortex is a necessary condition for perceptual processes and consciousness, such as occurs during waking and in an altered form during rapid eye movement sleep.

Consciousness↗

PubMed1999

Binding and the phenomenal unity of consciousness.

The binding problem is frequently discussed in consciousness research. However, it is by no means clear what the problem is supposed to be and how exactly it relates to consciousness. In the present paper the nature of the binding problem is clarified by distinguishing between different formulations of the problem. Some of them make no mention of consciousness, whereas others are directly related to aspects of phenomenal experience. Certain formulations of the binding problem are closely connected to the classical philosophical problem of the unity of consciousness and the currently fashionable search for the neural correlates of consciousness. Nonetheless, only a part of the current empirical research on binding is directly relevant to the study of consciousness. The main message of the present paper is that the science of consciousness needs to establish a clear theoretical view of the relation between binding and consciousness and to encourage further empirical work that builds on such a theoretical foundation.

Awareness↗

PubMed1995

Cerebral bases of consciousness: a historical view.

Attempts of modern brain research, starting at the end of the nineteenth century, to define and hierarchically order consciousness are reviewed. It is emphasized that roots from philosophy, biology, and psychology influenced brain research in its search for possible physical bases of consciousness. Among the mainstreams of research were approaches which defined consciousness by selecting numerous attributes of it and ordering these hierarchically. Similarly, there was widespread speculation on whether all kinds of animals or only some of them are conscious or manifest some of the hierarchically defined attributes of consciousness. On the brain side, the cerebral cortex and in particular its frontal aspects, the prefrontal cortex, was regarded as the principal anatomical basis of consciousness. The dependence of consciousness on memory and the ability to order processes in time were widely acknowledged and case descriptions from Korsakoff patients and epileptics were considered especially to demonstrate the interdependence between consciousness and the brain.

Alcohol Amnestic Disorder↗

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

Can midline brain shift be used as a prognostic factor to predict postoperative restoration of consciousness in patients with chronic subdural hematoma?

BACKGROUND AND PURPOSE: Our aim was to determine if midline brain shift could be used as a prognostic factor to predict postoperative restoration of consciousness in patients with CSDH. In these patients, we evaluated the relation (1) between midline brain shift as measured on CT and alteration of level of consciousness, and (2) between midline brain shift and restoration of consciousness after the operation. METHODS: Prospectively recorded data of 45 patients with CSDH were evaluated. We compared level of consciousness of patients measured by GCS score, brain displacement at PG and SP both in the preoperative and early postoperative period. RESULTS: Preoperatively, PG and SP shifts of the patients who were alert (GCS = 15) were significantly less than those of patients who had diminished consciousness. However, in patients with diminished consciousness (GCS < 15), the amount of lateral brain displacement and the degree of diminution of consciousness did not correlate. Those patients who had a preoperative SP shift of less than 10 mm had a significantly lesser chance to become alert after operation (2 of 5 patients) when compared with those patients who had a preoperative SP shift of 10 mm or more (21 of 23 patients). CONCLUSIONS: We conclude that preoperative SP shift may be used as a factor to predict restoration of consciousness in patients with CSDH; the likelihood of becoming alert after operation is increased if SP shift is 10 mm or greater, and is decreased if SP shift is less than 10 mm.

Adult↗

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↗