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At least 1,477 records · Page 82Linked to original sources
PubMed1999

ERPs obtained with the auditory oddball paradigm in coma and altered states of consciousness: clinical relationships, prognostic value, and origin of components.

OBJECTIVE: To study the event related potentials (ERPs) in coma and altered states of consciousness, their relationship with the clinical status and coma outcome. METHODS: ERPs were recorded with a passive auditory oddball paradigm in 103 patients. Their probability of occurrence and the peak latencies and amplitudes were studied as a function of the Glasgow Coma Score (GCS). Their relationship with outcome was studied in a subset of 83 patients examined within the first 4 days, and expressed in terms of sensitivity, specificity, and negative or positive prognostic values. RESULTS: When present, the ERPs to rare stimuli consisted of a fronto-central negativity (N(endog), mean latency: 330 ms) and a fronto-central positivity (P(endog), mean latency: 431 ms) following the exogenous N100-P200 complex. Both their probability of occurrence and their latencies and amplitudes were related with the GCS in anoxic and traumatic comas. The N(endog) and P(endog) had high sensitivity with a negative predictive value of 70% and 100%, respectively, but a low specificity, with a positive predictive value of 44% and 41%, respectively. CONCLUSIONS: ERPs can be recorded in some comatose patients and are likely to reflect implicit orienting processes rather than preserved consciousness. Their presence implies a good prognosis but no conclusion can be drawn from their absence.

Acoustic Stimulation↗
PubMed2001

Neurons in amygdala mediate ear pinna vasoconstriction elicited by unconditioned salient stimuli in conscious rabbits.

We determined whether functional integrity of neurons in the amygdala is necessary for sudden episodes of cutaneous vasoconstriction that occur when the conscious animal detects a salient alerting stimulus. To inhibit neuronal function, muscimol (5 nmol in 300 nl), a long acting and potent GABA-A receptor agonist that hyperpolarizes neurons, was injected bilaterally into the amygdala or into a more dorsal control site in conscious rabbits. Cutaneous blood flow was measured in the ear pinna flow using an ultrasonic Doppler probe chronically implanted around the central ear artery. Ear flow responses to salient unconditioned alerting stimuli (fur touch, slight cage movement. removal of drape covering cage) were examined before and after injection of the muscimol, and the effects compared with effects of muscimol on the ear flow response to more nociceptive stimuli, including ear pinch. Muscimol injections into the dorsal control site did not significantly alter alerting-related episodes of ear pinna vasoconstriction. Muscimol injections into the amygdala almost completely abolished ear vasoconstriction elicited by fur touch (0/5 positive responses), drape removal (0/7 positive responses) and cage movement (0/7 positive responses). Muscimol injections into the amygdala reduced the mean ear flow coefficient of variation for a 15 min observation period from 47+/-5 before injection to 15+/-33% after injection (P<0.01, n=7 rabbits). Muscimol injections into the amygdala did not alter the vigorous ear pinna vasoconstriction elicited by ear pinch (7/7 positive responses). Our results indicate that neuronal function in the amygdala, probably the central nucleus of the amygdala, is necessary for the occurrence of ear pinna vasoconstriction episodes elicited by unconditioned salient stimuli but not for the occurrence of corresponding vasoconstriction elicited by nociceptive stimuli.

Amygdala↗
PubMed2003

Cerebral metabolism and consciousness.

In vivo 13C magnetic resonance spectroscopy studies of the brain have measured rates of glutamate-glutamine cycle (Vcyc) and glucose oxidation (CMRglc(ox)) by detecting 13C label turnover from glucose to glutamate and glutamine. In both the awake human and in the anesthetized rat brains Vcyc and CMRglc(ox) are stoichiometrically related, and form a major pathway in which approximately 80% of the energy from glucose oxidation supports events associated with glutamate neurotransmission. The high energy consumption of the brain at rest and its quantitative usage for neurotransmission reflect a high level of neuronal activity for the non-stimulated brain. This high activity supports a reinterpretation of functional imaging data, e.g., where the large baseline signal has commonly been discarded. Independent measurements of energy consumption (delta CMRO2%) obtained from calibrated fMRI equaled percentage changes in neuronal spiking rate (delta nu %) measured by electrodes during sensory stimulation at two depths of anesthesia. These quantitative biophysical relationships between energy consumption and neuronal activity provide novel insights into the nature of brain function. The high resting brain activity is proposed to include the global interactions constituting the subjective aspects of consciousness. Anesthesia by lowering the total firing rates correlates with the loss of consciousness. These results, which measure the localized neuronal response and distinguish inputs of peripheral neurons from inputs of neurons from other brain regions, fit comfortably into the neuronal scheme of a global workspace proposed by Dehaene and Changeux.

Anesthesia↗
PubMed1999

Consciousness in congenitally decorticate children: developmental vegetative state as self-fulfilling prophecy.

According to traditional neurophysiological theory, consciousness requires neocortical functioning, and children born without cerebral hemispheres necessarily remain indefinitely in a developmental vegetative state. Four children between 5 and 17 years old are reported with congenital brain malformations involving total or near-total absence of cerebral cortex but who, nevertheless, possessed discriminative awareness: for example, distinguishing familiar from unfamiliar people and environments, social interaction, functional vision, orienting, musical preferences, appropriate affective responses, and associative learning. These abilities may reflect 'vertical' plasticity of brainstem and diencephalic structures. The relative rarity of manifest consciousness in congenitally decorticate children could be due largely to an inherent tendency of the label 'developmental vegetative state' to become a self-fulfilling prophecy.

Brain↗
PubMed2001

A sensorimotor account of vision and visual consciousness.

Many current neurophysiological, psychophysical, and psychological approaches to vision rest on the idea that when we see, the brain produces an internal representation of the world. The activation of this internal representation is assumed to give rise to the experience of seeing. The problem with this kind of approach is that it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness. An alternative proposal is made here. We propose that seeing is a way of acting. It is a particular way of exploring the environment. Activity in internal representations does not generate the experience of seeing. The outside world serves as its own, external, representation. The experience of seeing occurs when the organism masters what we call the governing laws of sensorimotor contingency. The advantage of this approach is that it provides a natural and principled way of accounting for visual consciousness, and for the differences in the perceived quality of sensory experience in the different sensory modalities. Several lines of empirical evidence are brought forward in support of the theory, in particular: evidence from experiments in sensorimotor adaptation, visual "filling in," visual stability despite eye movements, change blindness, sensory substitution, and color perception.

Brain↗
PubMed2002

The self-organizing consciousness.

We propose that the isomorphism generally observed between the representations composing our momentary phenomenal experience and the structure of the world is the end-product of a progressive organization that emerges thanks to elementary associative processes that take our conscious representations themselves as the stuff on which they operate, a thesis that we summarize in the concept of Self-Organizing Consciousness (SOC).

Association Learning↗
PubMed1999

Color, consciousness, and the isomorphism constraint.

The relations among consciousness, brain behavior, and scientific explanation are explored in the domain of color perception. Current scientific knowledge about color similarity, color composition, dimensional structure, unique colors, and color categories is used to assess Locke's "inverted spectrum argument" about the undetectability of color transformations. A symmetry analysis of color space shows that the literal interpretation of this argument--reversing the experience of a rainbow--would not work. Three other color to color transformations might work, however, depending on the relevance of certain color categories. The approach is then generalized to examine behavioral detection of arbitrary differences in color experiences, leading to the formulation of a principled distinction, called the "isomorphism constraint," between what can and cannot be determined about the nature of color experience by objective behavioral means. Finally, the prospects for achieving a biologically based explanation of color experience below the level of isomorphism are considered in light of the limitations of behavioral methods. Within-subject designs using biological interventions hold the greatest promise for scientific progress on consciousness, but objective knowledge of another person's experience appears impossible. The implications of these arguments for functionalism are discussed.

Color↗
PubMed1999

Microdialysis evaluation of the ocular pharmacokinetics of propranolol in the conscious rabbit.

PURPOSE: This study was conducted to assess the effects of anesthesia and aqueous humor protein concentrations on ocular disposition of propranolol. METHODS: Rabbits were anesthetized and a microdialysis probe was inserted into the anterior chamber of one eye; the contralateral eye served as a control. At timed intervals after probe placement, a 100-microl sample of aqueous humor was aspirated from each eye to determine protein concentration. In vitro protein binding parameters were used to simulate the impact of protein concentration on propranolol disposition. To assess the influence of anesthesia, probes were implanted in the anterior chamber of each eye. After >5-day stabilization, conscious and anesthetized rabbits (n = 3/group) received a 200-microg topical dose of [3H]DL-propranolol in each eye; propranolol was assayed in probe effluent. RESULTS: Changes in aqueous humor protein concentrations were observed following probe insertion. Simulations demonstrated that the unbound propranolol AUC (approximately 2.4-fold) in aqueous humor should be reduced due to protein influx. Intraocular propranolol exposure in anesthetized rabbits was approximately 8-fold higher than in conscious rabbits, and approximately 1.9-fold higher than in rabbits without a post-surgical recovery period. CONCLUSIONS: Anesthesia and time-dependent aqueous humor protein concentrations may alter ocular pharmacokinetics, and must be taken into account in the design of microdialysis experiments.

Adrenergic beta-Agonists↗
PubMed2004

Conscious processing of sexual information: mechanisms of appraisal.

To elucidate some of the activational mechanisms of sexual response, this study investigated the effects of conscious appraisal of sexual and neutral stimuli on a categorization task and on ratings of sexual arousal. Conscious appraisal is dependent on memory, regulatory, and attentional processes, interacting with one another. It is proposed that regulation is activated by attention, furnished by representations from implicit and explicit memory. Participants (26 men and 25 women) were asked to respond to "target" stimuli that were preceded by supraliminal "prime" stimuli. Primes and targets were operationalized by slides with sexual (i.e., romantic vs. explicit) and neutral content. In a cognitive task, participants had to group randomly presented targets as quickly as possible into sexual and nonsexual categories. Categorization of sexual targets was delayed when they were preceded by sexual primes compared to neutral primes. This was interpreted as an inhibitory process and compared with the Sexual Content-Induced Delay phenomenon (J. H. Geer & H. S. Bellard, 1996; J. H. Geer & J. S. Melton, 1997). No gender difference was found. In a subsequent affective task, participants provided an assessment of sexual arousal, followed by an evaluation of the target. This task was hypothesized to result in differential access to memory, where assessments of sexual arousal are influenced mainly by implicit memory, and where evaluations are influenced mainly by explicit memory. Gender differences were most prominent in the evaluation aspect of this task. It was concluded that cognitive processing of sexual information is similar for both genders, but that gender differences are present in affective processing of sexual information.

Adult↗
PubMed1999

Private self-consciousness and the five-factor model of personality: distinguishing rumination from reflection.

A distinction between ruminative and reflective types of private self-attentiveness is introduced and evaluated with respect to L. R. Goldberg's (1982) list of 1,710 English trait adjectives (Study 1), the five-factor model of personality (FFM) and A. Fenigstein, M. F. Scheier, and A. Buss's (1975) Self-Consciousness Scales (Study 2), and previously reported correlates and effects of private self-consciousness (PrSC; Studies 3 and 4). Results suggest that the PrSC scale confounds two unrelated, motivationally distinct dispositions--rumination and reflection--and that this confounding may account for the "self-absorption paradox" implicit in PrSC research findings: Higher PrSC scores are associated with more accurate and extensive self-knowledge yet higher levels of psychological distress. The potential of the FFM to provide a comprehensive framework for conceptualizing self-attentive dispositions, and to order and integrate research findings within this domain, is discussed.

Attention↗
PubMed2000

Semantic processing without conscious identification: evidence from event-related potentials.

Three event-related potential (ERP) experiments examined whether semantic content can be accessed from visually presented words that cannot be consciously identified. Category labels were shown to participants, followed by masked, briefly exposed words that were either exemplars of the category or not exemplars. The task was to verify the category, by guessing if necessary, and to identify the word, naming it if possible. Exposure durations were selected to allow identification in approximately half the trials. For identified words, there was a marked difference in the ERP response between in-category and out-of-category words because of an N400 component. For unidentified words, there was a similar although smaller difference. Conscious identification was defined using a variety of approaches: verbal report, 6-alternative forced choice, and binary categorization (in the context of the regression method; A. G. Greenwald, M. R. Klinger, & E. S. Schuh, 1995). By any definition, ERPs for unidentified words showed evidence of semantic processing. In addition, there were differences in the neuronal populations recruited to process above-threshold versus below-threshold words, suggesting qualitative differences.

Adult↗
PubMed1999

A dual-process model of defense against conscious and unconscious death-related thoughts: an extension of terror management theory.

Distinct defensive processes are activated by conscious and nonconscious but accessible thoughts of death. Proximal defenses, which entail suppressing death-related thoughts or pushing the problem of death into the distant future by denying one's vulnerability, are rational, threat-focused, and activated when thoughts of death are in current focal attention. Distal terror management defenses, which entail maintaining self-esteem and faith in one's cultural worldview, function to control the potential for anxiety that results from knowing that death is inevitable. These defenses are experiential, are not related to the problem of death in any semantic or logical way, and are increasingly activated as the accessibility of death-related thoughts increases, up to the point at which such thoughts enter consciousness and proximal threat-focused defenses are initiated. Experimental evidence for this analysis is presented.

Behavior Therapy↗
PubMed2005

Startle modulation during conscious emotion regulation is arousal-dependent.

Conscious regulation of negative emotion has been shown to affect human eyeblink startle responses, but whether these results depend on modulation of arousal- or valence-based processes is unknown. The authors presented participants with negative, neutral, and positive pictures and directed them to enhance, maintain, and suppress emotional responses. On emotional picture trials, startle responses decreased as a function of cue in the following order: enhance > maintain > suppress. Analysis of negative and positive picture trials separately revealed similar patterns of startle modulation by emotion regulation. There were no effects of emotion regulation on neutral trials. Results indicate that arousal, not valence, may be critical to startle modulation via conscious emotion regulation.

Adult↗
PubMed1999

Conscious awareness, memory and the hippocampus.

Declarative memory, the conscious recollection of past experiences, is known to involve the hippocampus. Now a study of amnesic patients shows that hippocampus-dependent learning can occur in the absence of conscious awareness.

Amnesia↗
PubMed1998

The anatomy of conscious vision: an fMRI study of visual hallucinations.

Despite recent advances in functional neuroimaging, the apparently simple question of how and where we see--the neurobiology of visual consciousness--continues to challenge neuroscientists. Without a method to differentiate neural processing specific to consciousness from unconscious afferent sensory signals, the issue has been difficult to resolve experimentally. Here we use functional magnetic resonance imaging (fMRI) to study patients with the Charles Bonnet syndrome, for whom visual perception and sensory input have become dissociated. We found that hallucinations of color, faces, textures and objects correlate with cerebral activity in ventral extrastriate visual cortex, that the content of the hallucinations reflects the functional specializations of the region and that patients who hallucinate have increased ventral extrastriate activity, which persists between hallucinations.

Brain Mapping↗
PubMed2003

A framework for consciousness.

Here we summarize our present approach to the problem of consciousness. After an introduction outlining our general strategy, we describe what is meant by the term 'framework' and set it out under ten headings. This framework offers a coherent scheme for explaining the neural correlates of (visual) consciousness in terms of competing cellular assemblies. Most of the ideas we favor have been suggested before, but their combination is original. We also outline some general experimental approaches to the problem and, finally, acknowledge some relevant aspects of the brain that have been left out of the proposed framework.

Action Potentials↗
PubMed1999

Cardiovascular effects of rilmenidine, moxonidine and clonidine in conscious wild-type and D79N alpha2A-adrenoceptor transgenic mice.

1. We investigated the cardiovascular effects of rilmenidine, moxonidine and clonidine in conscious wild-type and D79N alpha2A-adrenoceptor mice. The in vitro pharmacology of these agonists was determined at recombinant (human) alpha2-adrenoceptors and at endogenous (dog) alpha2A-adrenoceptors. 2. In wild-type mice, rilmenidine, moxonidine (100, 300 and 1000 microg kg(-1), i.v.) and clonidine (30, 100 and 300 microg kg(-1), i.v.) dose-dependently decreased blood pressure and heart rate. 3. In D79N alpha2A-adrenoceptor mice, responses to rilmenidine and moxonidine did not differ from vehicle control. Clonidine-induced hypotension was absent, but dose-dependent hypertension and bradycardia were observed. 4. In wild-type mice, responses to moxonidine (1 mg kg(-1), i.v.) were antagonized by the non-selective, non-imidazoline alpha2-adrenoceptor antagonist, RS-79948-197 (1 mg kg(-1), i.v.). 5. Affinity estimates (pKi) at human alpha2A-, alpha2B- and alpha2C-adrenoceptors, respectively, were: rilmenidine (5.80, 5.76 and 5.33), moxonidine (5.37, <5 and <5) and clonidine (7.21, 7.16 and 6.87). In a [35S]-GTPgammaS incorporation assay, moxonidine and clonidine were alpha2A-adrenoceptor agonists (pEC50/intrinsic activity relative to noradrenaline): moxonidine (5.74/0.85) and clonidine (7.57/0.32). 6. In dog saphenous vein, concentration-dependent contractions were observed (pEC50/intrinsic activity relative to noradrenaline): rilmenidine (5.83/0.70), moxonidine (6.48/0.98) and clonidine (7.22/0.83). Agonist-independent affinities were obtained with RS-79948-197. 7. Thus, expression of alpha2A-adrenoceptors is a prerequisite for the cardiovascular effects of moxonidine and rilmenidine in conscious mice. There was no evidence of I1-imidazoline receptor-mediated effects. The ability of these compounds to act as alpha2A-adrenoceptor agonists in vitro supports this conclusion.

Adrenergic alpha-Antagonists↗
PubMed2000

Cardiovascular and autonomic effects of omega-conotoxins MVIIA and CVID in conscious rabbits and isolated tissue assays.

1. The effects of a novel N-type voltage-operated calcium channel antagonist, omega-conotoxin CVID, were compared with omega-conotoxin MVIIA on sympathetic-evoked activation of right atria (RA), small mesenteric arteries (MA) and vasa deferentia (VD) isolated from the rat. Their effects were also compared on blood pressure and cardiovascular reflexes in conscious rabbits. 2. The pIC(50) values for MVIIA and CVID, respectively, for inhibiting sympathetic-evoked responses were equivalent in RA (8.7 and 8.7) and VD (9.0 and 8.7); however, in MA the values were 8.4 and 7.7. The cardiac to vascular (RA/MA) potency ratios, antilog (plog RA - plog MA), for MVIIA and CVID were 2 and 10. The offset rates for CVID and MVIIA were rapid, and peptide reapplication caused rapid onset of blockade, suggesting limited desensitization. 3. In the conscious rabbit, CVID and MVIIA (100 microg kg(-1) i.v.) caused a similar fall in blood pressure and a tachycardia that rapidly reached maximum. Both peptides decreased the vagal- and sympathetic-mediated components of the baroreflex, but had no effect on the vagal nasopharyngeal reflex. The orthostatic reflex to 90 degrees tilt was blocked by MVIIA with sustained postural hypotension for > or = 90 min after administration. In contrast, CVID caused postural hypotension at 30 min which recovered rapidly. 4. Neither CVID nor MVIIA (3 microg kg(-1) i.t.) significantly altered cardiovascular variables or autonomic reflexes. 5. In conclusion, CVID appears to be relatively weak at inhibiting the reflex response to tilt consistent with its weaker inhibition of rat mesenteric artery constriction to perivascular nerve stimulation. This may point to subtype N-type calcium channel selectivity.

Animals↗