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PubMed1997

[Sudden hyponatremia with unconsciousness. Case report and brief overview of the syndrome of inadequate antidiuresis (SIAD or Schwartz-Bartter syndrome].

A sixty-six year old female was admitted to the hospital with an incomplete hemiparesis on the left side combined with a short episode of unconsciousness. According to her husband's account she had a seizure. Relevant laboratory measurements: plasma sodium concentration 113.9 mmol/l, plasma concentration of ADH 10.3 pg/ml, urine sodium concentration 44.4 mmol/l. The plasma concentrations of creatinine and urea were within normal limits. The working hypothesis was SIAD (syndrome of inappropriate antidiuresis) or Schwartz-Bartter-syndrome. The patient was treated immediately with water restriction (500-1000 ml/day), furosemide and i.v. replacement of urinary sodium losses by 3% NaCl. The analysis of cerebrospinal fluid showed pleocytosis and increased concentrations of immunoglobulins G and M. Serological diagnosis was positive for antigen of varicella-zoster virus. These observations were thought to be compatible with a diagnosis of SIAD in the setting of encephalitis. Under water restriction, infusion of 3% saline, treatment with loop diuretics and aciclovir (3 x 750 mg daily) the neurological function returned to normal within 2 days. A standard oral water load on the 14th hospital days showed a return to a normal water metabolism.

Acyclovir↗
PubMedDate not supplied

[The role of unconscious sets formed on the basis of the perception of concrete visual stimuli and of illusory representations in conscious cognitive activity].

The cognitive set can be formed in healthy humans (75 subjects have been examined) on the basis of the Müller-Lyer's visual illusion. The effect of this set is expressed as a contrast illusion similar to the effect of the set, which is formed on the basis of the real size of visual stimuli (pictures of circles). Time of the simple motor reaction to the probe stimulus (light spot) depends on the factor of set stability. In subjects with the stable set the reaction time and its variability are substantially longer than in persons with the unstable set. Analysis of correctness of perception of the visual stimuli and the reaction time shows that the set which has been formed at the unconscious level leads to a certain rigidity in cognitive activity. Thus, factor of lability/stability of sets is an important feature of human cognitive activity.

Adult↗
PubMed1998

Replicable unconscious semantic priming.

In 4 experiments, subjects classified visually presented target words as pleasant-unpleasant words or male-female first names. Prime words were similar (congruent) or dissimilar (incongruent) in meaning to targets. Brief duration of prime words (17, 33, or 50 ms), along with pre- and postmasking, prevented most subjects from perceiving their physical and semantic properties. By constraining response latencies to fall within a response window--a narrow time band that occurred earlier than subjects would ordinarily respond--these experiments consistently produced subliminal priming effects, indicated by greater error rates for incongruent than congruent priming trials. This conclusion was confirmed by analyzing magnitude of priming as a regression function of prime perceptibility using the method of A. G. Greenwald, M. R. Klinger, and E. S. Schuh (1995). The data of each experiment passed their significant-intercept criterion for demonstrating unconscious cognition.

Cognition↗
PubMed2001

Functional magnetic resonance imaging and evoked potential correlates of conscious and unconscious vision in parietal extinction patients.

We describe recent functional magnetic resonance imaging (fMRI) and event-related potential (ERP) studies of visual extinction in patients with right parietal damage who can detect isolated visual stimuli on either side, yet often miss contralesional (left) stimuli during bilateral stimulation. We consider the neural fate of such extinguished visual stimuli and how neural responses differ for consciously detected versus extinguished stimuli. fMRI findings indicate that extinguished stimuli evoke activity in striate and ventral extrastriate visual cortex, despite escaping awareness. Activations for extinguished stimuli can be found even in category-specific (face-responsive) areas of the fusiform gyrus. On the other hand, activations in visual cortex are stronger for consciously detected versus extinguished stimuli, with parietal and frontal areas of the intact left hemisphere also implicated in this comparison. Recent ERP data likewise suggest differential neural responses for consciously detected versus extinguished stimuli. We discuss these findings in relation to current speculations about the neural basis of conscious and unconscious perception.

Attention↗
PubMedDate not supplied

Effect of unconscious interoceptive afferentation on the spatial organization of electrical activity in the human cerebral cortex.

Toposcopic studies consisting of EEG recording from 24 cortical points was carried out to characterize the spatial organization of the electrical activity of the human cerebral cortex during the action of unconscious interoceptive stimuli arising from biologically active points associated with different internal organs-the heart, lungs, liver, and intestine. When acupuncture had positive effects, reductions in global synchronization of cortical potentials were noted, which were combined with foci of weakening of the linear and nonlinear correlations in the anterior parts of the right hemisphere, as well as in the posterior and temporal parts of the left hemisphere, with increases in coherence in one of the high-frequency subranges of the EEG (21.5-23.0 Hz). Negative effects and absence of effect correlated with significantly less pronounced weakening of global synchronization of potentials, and increases in their coherence in one of the subranges of alpha activity.

Acupuncture Points↗
PubMed2004

Unconscious modulation of motor cortex excitability revealed with transcranial magnetic stimulation.

The neuronal effects of sensory events that do not enter conscious awareness have been reported in numerous pathological conditions and in normal subjects. In the present study, unconscious modulation of corticospinal excitability was probed in healthy volunteers with transcranial magnetic stimulation (TMS). TMS-induced motor evoked potentials (MEPs) were collected from the first dorsal interosseus muscle while subjects performed a masked semantic priming task that has been shown to elicit covert motor cortex activations. Our data show that the amplitude of the MEPs is modulated by an unseen prime, in line with temporal patterns revealed with event related potentials. These data confirm previous reports showing specific motor neural responses associated with an unseen visual stimulus and establish TMS as a valuable tool in the study of the neural correlates of consciousness.

Adult↗
PubMed1991

Differential influence of medial and lateral preoptic areas on body temperature in conscious and unconscious rats.

Since temperature sensitive neurons are unevenly distributed in the medial and the lateral preoptic areas, it was hypothesized that the two areas possibly would influence body temperature to a different extent. As alteration in sleep-wakefulness and body movement may affect the body temperature, experiments were conducted by reversible inactivation of those two areas, in freely moving (conscious) rats as well as in rats where changes in EEG and movement were restricted (unconscious). Results showed that the medial preoptic area is more effective in body temperature regulation. The study also revealed that the preoptic area mediated effect on body temperature regulation is not necessarily linked to simultaneous changes in sleep-wakefulness and alteration in the latter probably helps in maintaining the former within limit.

Anesthesia, General↗
PubMed1990

Conditions for versatile learning, Helmholtz's unconscious inference, and the task of perception.

It is a mistake to consider perception and learning separately because what one learns is strongly constrained by what one perceives, and what one perceives depends on what one has experienced. I shall propose the hypothesis that perception is the computation of a representation that enables us to make reliable and versatile inferences about associations occurring in the world around us--that is, perception prepares the ground for learning. The statistical problem in learning is to determine whether a compound event such as "C followed by U" is a random co-occurrence or a significant association, for if it is the former it would be a mistake to pay any particular attention to C, whereas if it is the latter C is a conditional stimulus for U and a useful predictor for it. Now you cannot decide whether the association is random or not without knowledge of the prior probabilities of C and U: hence on my hypothesis when you perceive an object or event the representation must not only signal "it's there" or "it's happened", but must also make evident (or rapidly accessible) the prior probability of what has been signalled. Furthermore it must do this for all the objects or events that can act as conditional stimuli, and this implies that the representative elements should be statistically independent (or approximately so) in the normal environment. Forms of coding that would do this, and the relationship with Helmholtz's unconscious inference, will be discussed. These considerations imply that the task performed in perception has been overlooked both by learning theorists and by connectionists working on associative and adaptive networks. Coding for independence may be particularly important in understanding the developmental processes during the sensitive period: it may be the operation that leads ontogenetically-timed, activity-dependent, connections to imprint appropriate codes if the animal has experience, but inappropriate codes without experience.

Adaptation, Physiological↗
PubMed2004

Dissociation between overt and unconscious face processing in fusiform face area.

The precise role of the fusiform face area (FFA) in face processing remains controversial. In this study, we investigated to what degree FFA activation reflects additional functions beyond face perception. Seven volunteers underwent rapid event-related functional magnetic resonance imaging while they performed a face-encoding and a face-recognition task. During face encoding, activity in the FFA for individual faces predicted whether the individual face was subsequently remembered or forgotten. However, during face recognition, no difference in FFA activity between consciously remembered and forgotten faces was observed, but the activity of FFA differentiated if a face had been seen previously or not. This demonstrated a dissociation between overt recognition and unconscious discrimination of stimuli, suggesting that physiological processes of face recognition can take place, even if not all of its operations are made available to consciousness.

Adult↗
PubMed2003

Dissecting out conscious and unconscious memory (sub)processes within the human medial temporal lobe.

The human medial temporal lobe (MTL) system mediates memories that can be consciously recollected. However, the specific natures of the individual contributions of its various subregions to conscious memory processes remain equivocal. Here we show a functional dissociation between the hippocampus proper and the parahippocampal region in conscious and unconscious memory as revealed by invasive recordings of limbic event-related brain potentials recorded during explicit and implicit word recognition: Only hippocampal and not parahippocampal neural activity exhibits a sensitivity to the implicit versus explicit nature of the recognition memory task. Moreover, only within the hippocampus proper do the neural responses to repeated words differ not only from those to new words but also from each other as a function of recognition success. By contrast parahippocampal (rhinal) responses are sensitive to repetition independent of conscious recognition. These findings thus demonstrate that it is the hippocampus proper among the MTL structures that is specifically engaged during conscious memory processes.

Brain Mapping↗
PubMed2003

Unconscious adaptation: a new illusion of depth induced by stimulus features without depth.

Here, we show a new illusion of depth induced by psychophysical adaptation to dynamic random-dot stereograms (RDS) that are interocularly anticorrelated (i.e., in which the images for the two eyes have reversed contrast polarity with each other). After prolonged viewing of anticorrelated RDS, the presentation of uncorrelated RDS (i.e., in which two images are mutually independent random-dot patterns) produces the sensation of depth, although both anticorrelated and uncorrelated RDSs are perceptually rivalrous with no consistent depth by themselves. Contrary to other aftereffects demonstrated in a number of visual dimensions, including motion, orientation, and disparity, this illusion results from unconscious adaptation; observers are not aware of what they are being adapted to during the process of adaptation. We further demonstrate that this illusion can be predicted from the simulated responses of disparity-selective neurons based on a local filtering model. Model simulations indicate that the inspection of anticorrelated RDS causes the adaptation of all disparity detectors except one sensitive to its disparity; therefore, those selectively unadapted detectors show relatively strong activation in response to the subsequent presentation of uncorrelated RDS and produce depth perception.

Adaptation, Psychological↗
PubMed2002

The electrophysiology of tactile extinction: ERP correlates of unconscious somatosensory processing.

We examined the electrophysiological correlates of left-sided tactile extinction in a patient with right-hemisphere damage. Computer-controlled punctate touch was presented to the left, right or both index fingers in an unpredictable sequence. The patient reported his conscious tactile percept ("left", "right" or "both"). He showed extinction on 75% of bilateral trials, reporting only right stimulation for these. Somatosensory evoked potentials for unilateral stimulation showed early components over contralateral somatosensory areas (P60 and N110) for either hand. In contrast to the results observed for age-matched controls, the patient's P60 was smaller in amplitude for left-hand touch over the right hemisphere than for right-hand touch over the intact hemisphere. Bilateral trials with extinction revealed residual P60 and N110 components over the right hemisphere in response to the extinguished left touch. These results demonstrate residual unconscious somatosensory processing of extinguished touch. They also suggest that tactile extinction can be caused by attenuation rather than elimination of somatosensory responses in the damaged hemisphere, with an underlying deficit even on unilateral trials.

Aged↗
PubMed2000

A conscious route to unconscious vision.

Damage to the primary visual cortex can leave subjects with unconscious residual vision, or 'blindsight'. New research suggests that 'top-down' modulation by intact conscious visual processes can improve performance in the impaired visual domain, even though that domain still remains quite inaccessible to consciousness.

Humans↗
PubMed2003

Absence of explicit and implicit memory in unconscious patients using a TCI of propofol.

BACKGROUND: Episodes of implicit memory have been described during propofol anaesthesia. It remains unclear whether implicit memory is caused by short periods of awareness or occurs in an unconscious subject. METHODS: Sixty patients were randomized in an experimental group (EG), a control group (CG) and a reference group (RG). Loss of consciousness (LOC) was obtained by progressive stepwise increases of propofol using a target-controlled infusion device (Diprifusor, Alaris Medical Systems, San Diego, CA). A tape containing 20 words was played to the patients in the CG before the start of anaesthesia and to the patients in the EG at a constant calculated concentration of propofol associated with LOC. The tape was not played to the patients in the RG. Three memory tests were performed postoperatively. RESULTS: Explicit and implicit memories were evidenced in the CG but not in the EG. CONCLUSION: In our group of young ASA I/II patients, in the absence of any noxious stimulus, no implicit or explicit memory was found when the calculated concentration of propofol using a Diprifusor was maintained at the level associated with LOC.

Adult↗
PubMed1998

Conscious and unconscious emotional learning in the human amygdala.

If subjects are shown an angry face as a target visual stimulus for less than forty milliseconds and are then immediately shown an expressionless mask, these subjects report seeing the mask but not the target. However, an aversively conditioned masked target can elicit an emotional response from subjects without being consciously perceived. Here we study the mechanism of this unconsciously mediated emotional learning. We measured neural activity in volunteer subjects who were presented with two angry faces, one of which, through previous classical conditioning, was associated with a burst of white noise. In half of the trials, the subjects' awareness of the angry faces was prevented by backward masking with a neutral face. A significant neural response was elicited in the right, but not left, amygdala to masked presentations of the conditioned angry face. Unmasked presentations of the same face produced enhanced neural activity in the left, but not right, amygdala. Our results indicate that, first, the human amygdala can discriminate between stimuli solely on the basis of their acquired behavioural significance, and second, this response is lateralized according to the subjects' level of awareness of the stimuli.

Adult↗
PubMed2001

Cerebral mechanisms of word masking and unconscious repetition priming.

We used functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) to visualize the cerebral processing of unseen masked words. Within the areas associated with conscious reading, masked words activated left extrastriate, fusiform and precentral areas. Furthermore, masked words reduced the amount of activation evoked by a subsequent conscious presentation of the same word. In the left fusiform gyrus, this repetition suppression phenomenon was independent of whether the prime and target shared the same case, indicating that case-independent information about letter strings was extracted unconsciously. In comparison to an unmasked situation, however, the activation evoked by masked words was drastically reduced and was undetectable in prefrontal and parietal areas, correlating with participants' inability to report the masked words.

Adult↗
PubMed1999

Verbal communication: what do critical care nurses say to their unconscious or sedated patients?

The importance of using verbal communication in the care of critically ill patients has long been known. Both qualitative and quantitative studies have presented evidence of the benefits of effective communication. This non-participant observational study aimed to explore how much and what types of verbal communication critical care nurses use when caring for unconscious or sedated patients. Sixteen critical care nurses were observed in 4-hour episodes and their verbal communication was transcribed and timed at source. Seven categories of verbal communication and a 'core concept' emerged on analysis of the raw data. Medical investigations/interventions performed on the patients increased the amount of communication used. The participants in this study were found to use a greater variety and amount of verbal communication than participants in other studies. The findings of this study highlight the need for formal support systems and continued education for nurses about the benefits of verbal communication.

Analgesia↗
PubMed1992

Implicit knowledge: new perspectives on unconscious processes.

Recent evidence from cognitive science and neuroscience indicates that brain-damaged patients and normal subjects can exhibit nonconscious or implicit knowledge of stimuli that they fail to recollect consciously or perceive explicitly. Dissociations between implicit and explicit knowledge, which have been observed across a variety of domains, tasks, and materials, raise fundamental questions about the nature of perception, memory, and consciousness. This article provides a selective review of relevant evidence and considers such phenomena as priming and implicit memory in amnesic patients and normal subjects, perception without awareness and "blindsight" in patients with damage to visual cortex, and nonconscious recognition of familiar faces in patients with facial-recognition deficits (prosopagnosia). A variety of theoretical approaches to implicit/explicit dissociations are considered. One view is that all of the various dissociations can be attributed to disruption or disconnection of a common mechanism underlying conscious experience; an alternative possibility is that each dissociation requires a separate explanation in terms of domain-specific processes and systems. More generally, it is concluded that rather than reflecting the operation of affectively charged unconscious processes of the kind invoked by psychodynamic or Freudian theorists, dissociations between implicit and explicit knowledge are a natural consequence of the ordinary computations of the brain.

Amnesia↗