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At least 1,639 records · Page 91Linked to original sources
PubMed2001

Power spectral analysis of the electroencephalogram during induced total spinal block.

PURPOSE: To evaluate the effects of total spinal block (TSB) on brain function, TSB-induced changes in cortical electrical activities were analyzed using power spectral analysis of an electroencephalogram (EEG). METHODS: Six patients suffering from chronic pain who were undergoing TSB therapy were studied. TSB was established with intrathecal 1% lidocaine (0.3 ml.kg(-1)) injected through the C1-2 lateral intervertebral space. Mechanical ventilation was continued via a laryngeal mask until the recovery of respiration. The EEG recording was started before TSB induction and continued until 10 min after extubation. The following processed EEG parameters were monitored: spectral edge frequency-90% (SEF90), spectral median frequency (SMF), and relative power in the frequency bands of delta, theta, alpha, beta, and the delta ratio [(alpha + beta)/delta]. RESULTS: TSB induced an unconscious state more than 40 min in all patients. During TSB, 12-13 Hz in SEF90 and 6-7 Hz in SMF were observed. These values are consistent with the previously reported prearousal threshold from general anesthesia. The other EEG descriptors did not change during the TSB-induced unconscious state. CONCLUSION: The dissociation of cortical electrical activities and the clinical coma-like condition may be characteristic of the TSB-induced unconscious state.

Journal Article↗
PubMed2005

Functional consequences of perceiving facial expressions of emotion without awareness.

A substantial body of research has established that even when we are not consciously aware of the faces of others we are nevertheless sensitive to, and impacted by their facial expression. In this paper, we consider this body of research from a new perspective by examining the functions of unconscious perception revealed by these studies. A consideration of the literature from this perspective highlights that existing research methods are limited when it comes to revealing possible functions of unconscious perception. The critical shortcoming is that in all of the methods, the perceived facial expression remains outside of awareness. This is a problem because there are good reasons to believe that one important function of unconsciously perceived negative faces is to attract attention so that they are consciously perceived; such conscious perception, however, is never allowed with existing methodologies. We discuss recent studies of emotional face perception under conditions of visual search that address this issue directly. Further, we suggest that methodologies that do not examine cognitive processes as they occur in more natural settings may result in fundamental misunderstandings of human cognition.

Attention↗
PubMedDate not supplied

[Affectivity in the nervous system].

Affectivity is an ambiguous term, related altogether to, mood, well-being, ill-being, emotional states, and at the same time to individual sensitivity, capacity to feel moved, as well as feelings and passions. We want to show that those states, as different as they may seem, belong to the perception by the central nervous system of past or present modifications, of an organism reacting to situations it has to cope with. Opposite to common opinion, this affectivity is not "generated" by the cerebral cortex but by the central brain. It results from memory input by the limbic system and from information processing by the hypothalamus and the reticular system, and from processing of mood and emotional rates provoked by self reactions in order to perpetuate survival, protection or one's own species. Considered as "favourable" or "unfavourable" after analyses by the limbic cortex, those states become in the central brain "pleasure" or "aversion", and generate motivation for action, to follow-on or to stop. From the limbic cortex, those motivations are transmitted to the contiguous prefrontal cortex. The prefrontal cortex is a center for action imitation. One may imagine it as a center for conscious cortical activity and for affective memory. This organisation of affectivity and affective memory settings in 2 different centers and at two different levels of the nervous system: the limbic cortex and the prefrontal neo-cortex. The prefrontal neo-cortex only is conscious, but the limbic cortex, although unconscious, is a source of motivation. One is led to describe an unconscious affectivity. It is impossible to talk about this affectivity without mentioning Freud's unconscious.

Functional Laterality↗
PubMed2004

Theories of visual awareness.

The past decade has provided a wealth of data for theorists of visual awareness. Two empirical approaches, both seeking to dissociate conscious from unconscious neural processes, have been particularly fruitful. The first has focused on the neural correlates of changes in experience occurring in the absence of change in external stimuli, for example during binocular rivalry; the second has investigated the neural correlates of unconscious processes such as blindsight. Several of the theories based on these data propose that visual consciousness arises from interactions between thalamo-cortical modules whose independent operation is unconscious; popular candidate 'modules' include visual regions in the 'ventral' visual pathway and parieto-frontal regions associated with action planning. These theories can be tested against recent findings from patients in the vegetative state, a state of 'wakefulness without awareness', which can follow major insults to the brain. The findings indicate that stimulus-evoked cortical activity occurs in the vegetative state, but tends to be limited in extent, is often restricted to primary sensory areas, and is poorly integrated with activity elsewhere in the cerebrum. The theories of visual awareness reviewed previously predict that such activity should not give rise to visual experience. This prediction is reassuring, but can we be sure that it is correct? Reflection on the indirect nature of the evidence available to theorists of visual awareness makes it doubtful that we can confidently specify the minimum conditions for awareness, unless we are prepared to modify our everyday concept of consciousness. O'Regan and Noe have recently proposed a sophisticated redefinition of visual awareness along these lines. Progress at this frontier of visual neuroscience requires that scientists and philosophers join forces to clarify the concepts of experience and consciousness.

Awareness↗
PubMed2005

Computational correlates of consciousness.

Over the past few years numerous proposals have appeared that attempt to characterize consciousness in terms of what could be called its computational correlates: Principles of information processing with which to characterize the differences between conscious and unconscious processing. Proposed computational correlates include architectural specialization (such as the involvement of specific regions of the brain in conscious processing), properties of representations (such as their stability in time or their strength), and properties of specific processes (such as resonance, synchrony, interactivity, or information integration). In exactly the same way as one can engage in a search for the neural correlates of consciousness, one can thus search for the computational correlates of consciousness. The most direct way of doing is to contrast models of conscious versus unconscious information processing. In this paper, I review these developments and illustrate how computational modeling of specific cognitive processes can be useful in exploring and in formulating putative computational principles through which to capture the differences between conscious and unconscious cognition. What can be gained from such approaches to the problem of consciousness is an understanding of the function it plays in information processing and of the mechanisms that subtend it. Here, I suggest that the central function of consciousness is to make it possible for cognitive agents to exert flexible, adaptive control over behavior. From this perspective, consciousness is best characterized as involving (1) a graded continuum defined over quality of representation, such that availability to consciousness and to cognitive control correlates with properties of representation, and (2) the implication of systems of meta-representations.

Cognition↗
PubMed2005

General anesthesia and the neural correlates of consciousness.

The neural correlates of consciousness must be identified, but how? Anesthetics can be used as tools to dissect the nervous system. Anesthetics not only allow for the experimental investigation into the conscious-unconscious state transition, but they can also be titrated to subanesthetic doses in order to affect selected components of consciousness such as memory, attention, pain processing, or emotion. A number of basic neuroimaging examinations of various anesthetic agents have now been completed. A common pattern of regional activity suppression is emerging for which the thalamus is identified as a key target of anesthetic effects on consciousness. It has been proposed that a neuronal hyperpolarization block at the level of the thalamus, or thalamocortical and corticocortical reverberant loops, could contribute to anesthetic-induced unconsciousness. However, all anesthetics do not suppress global cerebral metabolism and cause a regionally specific effect on thalamic activity. Ketamine, a so-called dissociative anesthetic agent, increases global cerebral metabolism in humans at doses associated with a loss of consciousness. Nevertheless, it is proposed that those few anesthetics not associated with a global metabolic suppression effect might still have their effects on consciousness mediated at the level of thalamocortical interactions, if such agents scramble the signals associated with normal neuronal network reverberant activity. Functional and effective connectivity are analysis techniques that can be used with neuroimaging to investigate the signal scrambling effects of various anesthetics on network interactions. Whereas network interactions have yet to be investigated with ketamine, a thalamocortical and corticocortical disconnection effect during unconsciousness has been found for both suppressive anesthetic agents and for patients who are in the persistent vegetative state. Furthermore, recovery from a vegetative state is associated with a reconnection of functional connectivity. Taken together these intriguing observations offer strong empirical support that the thalamus and thalamocortical reverberant network loop interactions are at the heart of the neurobiology of consciousness.

Anesthesia, General↗
PubMed1997

Analysis of risk factors for nosocomial infections--results from the first national prevalence survey in Germany (NIDEP Study, Part 1).

An analysis of risk factors for nosocomial infections (NI) was carried out using data from the first national prevalence survey on NI in Germany. Fourteen thousand, nine hundred and sixty-six patients, with a total of 543 NI, were included. Urinary tract infections (UTI), lower respiratory tract infections (LRTI), surgical site infections (SSI) and primary septicaemia (PS) were analysed. UTI were significantly associated with unconsciousness, age, prior operation, hospital size and female sex (P < 0.1). LRTI were significantly associated with chronic airway disease, intensive care units, unconsciousness, polytrauma, prior operation, cardiovascular disease, malignancy and absence of infection on admission. The department, age, diabetes mellitus, male sex and hospital size were risk factors for SSI. The department, prior operation and unconsciousness were significantly associated with PS. An investigator effect was observed for LRTI and PS. Although no final conclusions from a risk factor analysis based on prevalence data can be drawn the results support stratification of NI for routine surveillance.

Adult↗
PubMed1988

Routine pelvic radiography in severe blunt trauma: is it necessary?

To evaluate the hypothesis that all victims of severe blunt trauma require a pelvic radiograph, we prospectively studied all such patients admitted to the Southern New Jersey Regional Trauma Center during a seven-month period. All patients were classified as unconscious; impaired; awake, alert, and symptomatic; or alert, oriented, and asymptomatic for pelvic fracture on admission. All underwent a plain anterior-posterior radiograph of the pelvis. A total of 265 patients were studied and 26 pelvic fractures were identified. These occurred in seven of 36 unconscious patients, 11 of 96 impaired patients, and eight of 23 symptomatic patients. No fractures were identified in 110 awake, alert, oriented, and asymptomatic patients (P less than .0001). We conclude that pelvic radiographs are required in unconscious or impaired victims of severe blunt trauma and those with signs or symptoms of pelvic fractures but are not required in the awake, alert, and asymptomatic patient.

Adult↗
PubMed1999

Prediction of neurological outcome after cardiopulmonary resuscitation.

In 231 patients with circulatory arrest of primary cardiovascular or pulmonary aetiology guidelines were established for predicting neurological outcome within the first year after cardiopulmonary resuscitation. Outcome measures were brain death, persistent unconsciousness, persistent disability after awakening and complete recovery. A total of 116 patients remained unconscious while 115 regained consciousness. Brain stem areflexia with apnoea (brain death) was demonstrated in 40 patients. No other finding per se could predict a specific outcome. The time for recovery of individual neurological functions seemed to be the key to prognostication. Testing the caloric vestibular reflex or stereotypic reactivity thus differentiated patients regaining consciousness from those remaining unconscious, with positive predictive values of 0.79 and 0.77 at 1 h and negative values of 1.0 and 0.97 at 24 h as compared with 50/50 prior odds. The presence of speech at 24 h or the ability to cope with personal necessities at 72 h predicted complete recovery with positive predictive values of 0.91 and 0.92 as compared with prior odds of 0.17, whereas, the negative predictive values never exceeded prior odds of 0.83.

Brain Death↗
PubMed1997

The Transition from Automatic to Controlled Processing.

The transition from automatic (unconscious) to controlled (conscious) processing is described in terms of a neural network model of classical conditioning ([Schmajuk et al., 1996]). In the framework of the network, an environmental stimulus is processed in controlled or conscious mode when Novelty and attention to the stimulus are large, and in automatic or unconscious mode otherwise. In the model, indirect dopamine (DA) agonists, such as amphetamine or nicotine, enhance the DA representation of Novelty, thereby increasing attention and engaging conscious processing of environmental stimuli. By contrast, DA receptor antagonists, such as haloperidol, reduce the DA representation of Novelty, thereby decreasing attention, and engaging unconscious processing of the stimuli.

Journal Article↗
PubMed1996

Human colour discrimination based on a non-parvocellular pathway.

BACKGROUND: Traditionally, colour information is assumed to be carried by neural channels in the parvocellular pathway and to be encoded in an opponent manner, while other, non-parvocellular, spectrally non-opponent channels are thought to play no part in colour vision. But is the parvocellular pathway the only way that colours can be discriminated in human vision? We studied two patients with cerebral achromatopsia, who lack conscious colour perception but are nevertheless able to make use of colour information. In particular, we investigated whether, in these patients, colour discrimination is mediated by the parvocellular pathway. RESULTS: The achromatopsic patients carried out a forced-choice colour- and luminance-discrimination task, and showed clear evidence of unconscious colour processing, consistent with previous studies. We added different types of luminance noise to see when this unconscious colour information could be masked. The results of the colour-discrimination-with-noise and the brightness-non-additivity experiments showed a double-dissociation between patients. This indicates that, in one patient, unconscious colour discrimination may be subserved by a spectrally non-opponent mechanism, which does not have the characteristics of the parvocellular pathway and which is responsive to fast flicker. Spectral sensitivity, contrast sensitivity and motion perception experiments confirmed that this patient lacks a working opponent parvocellular system. The second achromatopsic patient showed evidence of a residual parvocellular system. CONCLUSIONS: Our results show that chromatic discrimination need not be mediated by neural mechanisms, the parvocellular system in particular, normally assumed to subserve conscious colour perception. Such discrimination may be mediated by a neural subsystem which responds to fast flicker, is spectrally non-opponent, and supports normal motion perception.

Aged↗
PubMed2003

Dynamic variations in affective priming.

The present study investigates the dynamics of emotional processing and awareness using an affective facial priming paradigm in conjunction with a multimodal assessment of awareness. Key facial primes are visually masked, and are presented for brief (unconscious) and extended (conscious) durations. Using a preference measure, we examine whether the effects of the primes differ qualitatively (Murphy & Zajonc, 1993). We show that: (a) unconscious affective priming with faces emerges strongly in initial presentations and diminishes rapidly with repetition; (b) conscious affective priming also emerges strongly in initial presentations, however it persists in strength with repetition; and (c) in contrast to other reports on the salience of negative stimuli, happy faces appear more salient than sad faces when presented outside awareness. We discuss the limits and extensions of unconscious affective priming with faces, and consider several methodological and conceptual questions concerning emotional processing out of awareness.

Adolescent↗
PubMed1997

Unexpected awareness and memory in the perianesthesia setting.

Unexpected awareness and memory with general anesthesia are phenomena that can occur in the intriguing interface between consciousness and unconsciousness. Studies suggest that, for some patients, cognitive processing remains active even during deep anesthesia; that is, an apparently unconscious patient still may be registering information. Although explicit memory is usually eliminated by general anesthesia, implicit or subconscious memory may remain. There is no monitor to tell where the patient lies on the continuum between consciousness and unconsciousness. "Sleeping" patients are vulnerable to overhearing inappropriate conversation that may have negative consequences. Post-traumatic stress disorder as well as medical malpractice litigation may result from awareness or memory during anesthesia. Implications for the use of opioids, benzodiazepines, and muscle relaxants in the perianesthesia setting as well as nursing interventions addressing unexpected awareness or memory are discussed.

Anesthesia, General↗
PubMed2001

Intracerebral event-related potentials to subthreshold target stimuli.

OBJECTIVES: Event-related potentials (ERPs) elicited by subthreshold visual stimuli were recorded directly from human frontal and temporal lobe structures to study unconscious perception. METHODS: Thirteen intractable epileptic patients undergoing depth electrode recordings prior to their surgical treatment participated in the study. An original method of modified visual oddball paradigm with supraliminal and subliminal stimuli was applied, and the averaged responses to both kinds of stimuli were subsequently compared. RESULTS: The results clearly prove that, at least from an electrophysiological viewpoint, the mechanism of unaware processing of visual stimuli in the human brain does not differ substantially from the aware processing. Finding the subliminal P3 waveform in a number of cortical structures (hippocampus and parahippocampal gyrus bilaterally, and left-sided mesiofrontal, orbitofrontal and lateral temporal cortex) indicates their involvement in unconscious processing, in spite of the fact that typical large-scale neurocognitive networks are not completely activated. The absence of activation consistently observed bilaterally in dorsolateral prefrontal cortices, in connection with right-sided cortical frontal lobe structures and right-sided lateral temporal neocortex in unconscious perception, supports the importance of these structures for the awareness of visual stimuli. The proof of the significantly faster unaware information processing represents another distinctive feature of implicit visual perception. CONCLUSIONS: Based on the presented findings and comparisons with the results of previous ERP, functional magnetic resonance imaging, positron emission tomography, and clinical neuropsychological studies, a crucial role of the large-scale neural system for conscious experience of perception is suggested, which is distributed extensively among the dorsal posterior association areas and the prefrontal cortex, with the dominant part being that of the right hemisphere.

Adult↗
PubMed1996

Triphasic waves during post-ictal stupor.

BACKGROUND: The term, "triphasic wave" originally described an EEG pattern believed to be a marker for a specific stage of hepatic coma. For 4 decades, the diagnostic and prognostic specificity of the pattern remains controversial. Its pathophysiology also continues to be elusive. METHODS: EEG recordings were obtained in three patients known or suspected to have primary generalized epilepsy. In 2 patients, the EEGs were part of long-term monitoring using simultaneous video-EEG telemetry. For the third patient, the EEG was secured only during the post-ictal unconsciousness. These 3 patients were specifically selected because of the presence of triphasic waves in their EEGs. RESULTS: Triphasic waves were observed in the EEG of the 3 patients only during post-ictal unconsciousness. The pattern was transient, being preceded by generalized suppression and delta slow waves and followed by theta activities. Alpha rhythms supervened when the patients became fully alert. CONCLUSION: A post-ictal state should be considered in unconscious patients with triphasic EEG waves.

Adult↗
PubMed2001

What do nurses and therapists think about the positioning of stroke patients?

BACKGROUND: At present, there are a number of different positioning strategies for stroke patients, but these are mainly based on clinical experience rather than research. Prior to developing a study to evaluate the effect of positioning on outcome after stroke, it was important to establish if nurses in our hospital had given much thought to the positioning of stroke patients. AIM OF THE STUDY: This study aimed to explore whether nurses working on the stroke unit at a Scottish teaching hospital held different views on the positioning of conscious and unconscious stroke patients to nurses working on other wards with stroke patients and therapists. METHODS: Questionnaires on various aspects of patient positioning were sent to 150 nurses and 25 therapists working in five specialities where stroke patients are cared for in a large teaching hospital. FINDINGS: Overall, the majority of nurses and therapists (74%) believed that the best position for conscious stroke patients was sitting in a chair. Also, 80% of them believed that the best position for unconscious stroke patients was lying on the nonparetic side. There was less of a consensus between nurses and therapists working in the five specialities as to whether it was appropriate for conscious or unconscious stroke patients to lie on their paretic side, lie supine or sit propped-up in bed in either a 30 or 70 degrees angle. CONCLUSIONS: The lack of consensus between nurses working in the five specialities is probably because at present there is little research to guide nursing practices for the positioning of stroke patients. Therefore, research to confirm which positions improves or hinders outcome after stroke is essential. Indeed, positioning is a simple inexpensive strategy, which could have a substantial public health impact, as stroke is so common.

Attitude of Health Personnel↗
PubMed1977

[The "locked-in" syndrome: pseudocoma in thrombosis of the basilar artery (author's transl)].

In pontine lesions with tetraplegia and cranial-nerve disturbances--including trismus--and with speech disability paralytic akinesia and loss of reactivity may be misinterpreted as coma. "Pseudocoma" of this kind may be associated with normal consciousness or relatively mild psychological disorders. This explains the discrepancy between a normal EEG (only minor abnormalities) and presumed unconsciousness. The term "locked-in" expresses the patient's inability to communicate. In typical cases there may be only vertical eye movements and blinking. Using remaining innervation facilities, those examining and treating the patient must try to communicate with him. The locked-in state may be mistaken for coma particularly if there had been a preceding episode of unconsciousness. Moreover, the "locked-in" syndrome often passes into a state of unconsciousness or coma. The degree of communication can markedly differ from hour to hour. Most of the cases of this syndrome are caused by basilar artery thrombosis.

Adult↗
PubMed1983

The use of dreams in couples therapy.

Spouses and family members communicate in complex, highly developed patterns which are largely out of awareness (Wynne 1961; Martin 1976; Cavenar 1979; Satir 1964). The therapist's grasp of these patterns of unconscious relatedness is essential to effective couples therapy or family therapy. This becomes a basis for interventions designed to help change those patterns destructive to a mutually satisfying relationship. A dream which one member of a couple presents in the setting of conjoint therapy is an important moment in which unconscious communication becomes manifest. Awareness and effectiveness can be enhanced when a therapist emphasizes the interpersonal dimension of the dream rather than treating it as a purely intrapsychic event. We examine meanings and uses of dreams shared in the context of couples psychotherapy, via literature review, clinical examples, and discussion. We suggest an approach which highlights interpersonal dimensions of dream-sharing and incorporates a concept of unconscious resonance.

Adult↗