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PubMed2006

Unconscious modulation of the conscious experience of voluntary control.

How does the brain generate our experience of being in control over our actions and their effects? Here, we argue that the perception of events as self-caused emerges from a comparison between anticipated and actual action-effects: if the representation of an event that follows an action is activated before the action, the event is experienced as caused by one's own action, whereas in the case of a mismatch it will be attributed to an external cause rather than to the self. In a subliminal priming paradigm we show that participants overestimated how much control they had over objectively uncontrollable stimuli, which appeared after free- or forced-choice actions, when a masked prime activated a representation of the stimuli immediately before each action. This prime-induced control-illusion was independent from whether primes were consciously perceived. Results indicate that the conscious experience of control is modulated by unconscious anticipations of action-effects.

Adult↗
PubMed2004

From sensory processes to conscious perception.

In recent years, cognitive neuroscientists have began to explore the process of how sensory information gains access to awareness. To further probe this process, event-related functional magnetic resonance imaging (fMRI) was used while testing subjects with a paradigm known as the "attentional blink." In this paradigm, visually presented information sporadically fails to reach awareness. It was found that the magnitude and time course of activation within the anterior cingulate (BA 32), medial prefrontal cortex (BA 9), and frontopolar cortex (BA 10) predicted whether or not information was consciously perceived during the critical period for the attentional blink. These results are discussed in light of a neural framework for conscious processing.

Adolescent↗
PubMed2004

Hemisphere differences in conscious and unconscious word reading.

Hemisphere differences in word reading were examined using explicit and implicit processing measures. In an inclusion task, which indexes both conscious (explicit) and unconscious (implicit) word reading processes, participants were briefly presented with a word in either the right or the left visual field and were asked to use this word to complete a three-letter word stem. In an exclusion task, which estimates unconscious word reading, participants completed the word stem with any word other than the prime word. Experiment 1 showed that words presented to either visual field were processed in very similar ways in both tasks, with the exception that words in the right visual field (left hemisphere) were more readily accessible for conscious report. Experiment 2 indicated that unconsciously processed words are shared between the hemispheres, as similar results were obtained when either the same or the opposite visual field received the word stem. Experiment 3 demonstrated that this sharing between hemispheres is cortically mediated by testing a split-brain patient. These results suggest that the left hemisphere advantage for word reading holds only for explicit measures; unconscious word reading is much more balanced between the hemispheres.

Adult↗
PubMed2004

Anomalous control: when 'free-will' is not conscious.

The conscious feeling of exercising 'free-will' is fundamental to our sense of self. However, in some psychopathological conditions actions may be experienced as involuntary or unwilled. We have used suggestion in hypnosis to create the experience of involuntariness (anomalous control) in normal participants. We compared a voluntary finger movement, a passive movement and a voluntary movement suggested by hypnosis to be 'involuntary.' Hypnosis itself had no effect on the subjective experience of voluntariness associated with willed movements and passive movements or on time estimations of their occurrence. However, subjective time estimates of a hypnotically-suggested, 'involuntary' finger movement were more similar to those for passive movements than for voluntary movements. The experience of anomalous control is qualitatively and quantitatively different from the normal conscious experience of a similar act produced intentionally. The experience of anomalous control may be produced either by pathology, or, in our case, by suggestion.

Adolescent↗
PubMed2004

Brain stimulation and conscious experience.

Libet discovered that a substantial duration (> 0.5-1.0 s) of direct electrical stimulation of the surface of the somatosensory cortex at threshold currents is required before human subjects can report that a conscious somatosensory experience had occurred. Using a reaction time method we confirm that a similarly long stimulation duration at threshold currents is required for activation of elementary visual experiences (phosphenes) in human subjects following stimulation of the surface of the striate cortex. However, the reaction times for the subject to respond to the cessation of the visual experience after the end of electrical stimulation could be as brief as 225-242 ms. We also carried out extensive studies in cats under a variety of anesthetic conditions using the same electrodes and parameters of stimulation employed in the human studies to study the patterns of neuronal activity beneath the stimulating surface electrode. Whereas sufficiently strong currents can activate neurons within milliseconds, stimulating currents close to threshold activate sustained neural activity only after at least 350-500 ms. When currents are close to threshold, some neurons are inhibited for several hundreds of millisecond before the balance between inhibition and excitation shifts towards excitation. These results suggest that the prolonged latencies, i.e., latencies beyond 200-250 ms, for the emergence of conscious experience following direct cortical stimulation result from a delay in the sustained activation of underlying cortical neurons at threshold currents rather than being due to any unusually long duration in central processing time. Intracellular records from cortical neurological cells during repetitive electrical stimulation of the surface of the feline striate cortex demonstrate that such stimulation induces a profound depolarizing shift in membrane potential that may persist after each stimulus train. Such a depolarization is evidence that extracellular K+ concentrations have increased during electrical stimulation. Such an increase in extracellular K+ progressively increases cortical excitability until the threshold for sustained activation of cortical neurons is reached and then exceeded. Consequently, the long latency for threshold activation of cortical neurons depends upon a dynamically increasing cortical facilatory process that begins hundreds of milliseconds before there is sustained activation of such neurons. In some cases, this facilatory process must overcome an initial stimulus-induced inhibition before neuronal firing commences.

Adult↗
PubMed2004

Identifying neural correlates of consciousness: the state space approach.

This article sketches an idealized strategy for the identification of neural correlates of consciousness. The proposed strategy is based on a state space approach originating from the analysis of dynamical systems. The article then focuses on one constituent of consciousness, phenomenal awareness. Several rudimentary requirements for the identification of neural correlates of phenomenal awareness are suggested. These requirements are related to empirical data on selective attention, on completely intrinsic selection and on globally unconscious states. As an example, neuroscientific findings on synchronized gamma activity are categorized according to these requirements.

Attention↗
PubMed2005

Consciousness eclipsed: Jacques Loeb, Ivan P. Pavlov, and the rise of reductionistic biology after 1900.

The life sciences in the 20th century were guided to a large extent by a reductionist program seeking to explain biological phenomena in terms of physics and chemistry. Two scientists who figured prominently in the establishment and dissemination of this program were Jacques Loeb in biology and Ivan P. Pavlov in psychological behaviorism. While neither succeeded in accounting for higher mental functions in physical-chemical terms, both adopted positions that reduced the problem of consciousness to the level of reflexes and associations. The intellectual origins of this view and the impediment to the study of consciousness as an object of inquiry in its own right that it may have imposed on peers, students, and those who followed is explored.

Behaviorism↗
PubMed2005

Brain stimulation and conscious experience: electrical stimulation of the cortical surface at a threshold current evokes sustained neuronal activity only after a prolonged latency.

Libet demonstrated that a substantial duration (>0.5-1.0 s) of direct electrical stimulation of the surface of a sensory cortex at a threshold or liminal current is required before a subject can experience a percept. Libet and his co-workers originally proposed that the result could be due either to spatial and temporal facilitation of the underlying neurons or additionally to a prolonged central processing time. However, over the next four decades, Libet chose to attribute the prolonged latency for evoking conscious experience to a prolonged central processing time. In my view, Libet has not provided any convincing evidence, either on the basis of his own past work or in his critique of my paper, for his hypothesis of a central processing time exceeding 0.5s before conscious experience emerges following direct electrical threshold stimulation of the cortical surface. I stand by my original results and conclusion that such prolonged latencies are largely the consequence of a dynamically increasing cortical facilitatory process that begins hundreds of milliseconds before there is a sustained neuronal activation. In some cases, the facilitatory process must overcome an initial stimulus-induced inhibition before neuronal firing commences.

Consciousness↗
PubMed2006

Consciousness of the self (COS) and explicit knowledge.

Starting with distinction between explicit and implicit knowledge and the traditional philosophical distinction between COS (the consciousness of self) as an object and COS as a subject, we suggest a triple classification of COS experience into three modes, each corresponding to a different state of consciousness. When one acts automatically COS is totally embedded within the representation of the environment. When one monitors or attends to one's experience, the self is implied by an explicit representation of one's attitudes, consistent with Descartes' cogito insight 'I think therefore I am' (1641,1984). However, a reflexive thought, e.g., 'I know fact x,' requires an explicit representation of the self. This analysis highlights the existence of an intermediate mode of COS as a subject and suggests its possible connection to monitoring one's behavior.

Cognition↗
PubMed2026

Modulation of heart rate and heart rate variability during animal-assisted treatment of patients in a minimally conscious state: A randomized controlled crossover study.

BACKGROUND: Animal-assisted treatment (AATx) is a promising and increasingly used approach in neurorehabilitation, yet its psychophysiological effects remain largely unexplored. Patients in a minimally conscious state (MCS) show severely altered consciousness with minimal but definite behavioral signs of awareness. Because behavioral assessment in this population is limited, psychophysiological measures such as heart rate (HR) and heart rate variability (HRV) may offer valuable insights into autonomic regulation during therapy. AIM: The present study investigated whether AATx influences HR and HRV compared to treatment as usual (TAU). METHODS: A randomized controlled crossover design with repeated measures was conducted. HR and HRV data were recorded using an Empatica E4 wristband, and linear mixed-effects models were fitted for each outcome variable. The analytic sample included twenty-one patients with MCS who completed at least one of the four sessions. RESULTS: We found a significant decrease in mean HR (estimate = -12.75, p = .041) and a significant increase in the standard deviation of normal-to-normal intervals (SDNN) (estimate = 15.76, p = .020) during AATx compared to TAU from the pretreatment to the posttreatment phase, indicating enhanced parasympathetic activation and greater autonomic flexibility. Other HRV parameters revealed no significant effects of AATx, though trends were consistent with the hypotheses. CONCLUSIONS: These findings provide preliminary physiological evidence that AATx can modulate autonomic activity in MCS patients. Despite limitations related to sample size and recording quality, the results highlight the potential of AATx as an emotionally engaging intervention in early neurorehabilitation.

Humans↗
PubMed2006

Cognitive self-consciousness, implicit learning and obsessive-compulsive disorder.

The negative appraisal of commonly experienced intrusive thoughts is posited to play an important role in obsessive-compulsive disorder (OCD), although why some people focus on thought experiences and have difficulties dismissing intrusions is not well understood. To elucidate how intrusive thoughts might become obsessional problems, relations between thought-focused attention (cognitive self-consciousness; CSC), implicit sequence learning and OCD were evaluated in individuals with OCD (n=43) and in a nonclinical comparison group (n=41). Impaired performance on a serial reaction time test, but enhanced recognition of the embedded stimulus pattern, was predicted for the OCD group based on hypothesized nonconscious processing differences. Predicted differences were found and CSC score predicted reaction time and pattern recognition. CSC might be a consequence of conscious processing gating problems that increase thought salience and the likelihood of the negative appraisal of intrusive thoughts. Implications for theory and treatment are discussed.

Adolescent↗
PubMed2005

Rapid fluctuations in conscious state in a patient with an extensive spinal dural fistula.

A man with a spontaneous spinal dural fistula and significant fluctuations in level of consciousness is discussed. The presentation was that of headache and vomiting followed by an initially enigmatic acute reduction in the level of consciousness. This required urgent evacuation of bilateral chronic subdural haematomas, believed to be causative. Following mobilisation, several episodes of presumed orthostatic intracranial hypotension occurred rendering the patient rapidly unconscious. A large spinal extradural CSF collection extending through the full length of the vertebral canal was later diagnosed however, the precise location of the fistulous leak could not be found radiologically. Non-operative management was successful. To the best of our knowledge, this is the first description of a spontaneous spinal cerebrospinal fluid leak of this magnitude. The case, pathogenesis, investigations and management of this rare entity are considered and the literature reviewed.

Cervical Vertebrae↗
PubMed2006

Neuronal information coding by oscillation phase prediction error: implications for consciousness and control of voluntary function.

Neuronal oscillatory firing patterns are widely thought to serve as coincidence detectors, so as to synchronize information processing across brain regions. I hypothesize here that, instead, oscillatory function can be better understood by reversing conventional models and regarding oscillations slower than 30 Hz as background activity occurring in the absence of conscious or voluntary function. Action potentials occurring out of phase with the local population oscillation then emerge as information carriers, according to a prediction error mechanism that was first described in the drug abuse literature. Shannon information calculations show that coding by out-of-phase action potentials is far more efficient than are conventional synchronization models, and a simple calculation of the degree to which an action potential is out of phase correctly predicts the amount of information content. This model appears to account for a wide range of existing experimental observations of visual attention, voluntary motor function, and movement disorders. It also suggests an intuitively simple way of understanding consciousness, based upon a "self-observing" feedback mechanism of neocortical neurons firing out of phase. The hypothesis also suggests that the function of slow-wave sleep may be to re-entrain desynchronized oscillations.

Action Potentials↗
PubMed2006

Alienation, recovered animism and altered states of consciousness.

Alienation is the feeling that life is 'meaningless', that we do not belong in the world. But alienation is not an inevitable part of the human condition: some people do feel at one with the world as a consequence of the animistic way of thinking which is shared by children and hunter-gatherers. Animism considers all significant entities to have 'minds', to be 'alive', to be sentient agents. The animistic thinker inhabits a world populated by personal powers including not just other human beings, but also important animals and plants, and significant aspects of physical landscape. Humans belong in this world because it is a web of social relationships. Animism is therefore spontaneous, the 'natural' way of thinking for humans: all humans began as animistic children and for most of human evolutionary history would have grown into animistic adults. It requires sustained, prolonged and pervasive formal education to 'overwrite' animistic thinking with the rationalistic objectivity typical of the modern world. It is this learned abstraction that creates alienation--humans are no longer embedded in a world of social relations but become estranged, adrift in a world of indifferent things. Methods used to cure alienation and recover animistic modes of thinking involve detachment from the social systems that tend to maintain objectivity and rationality: for example, solitude, leisure, unstructured time and direct contact with nature. Many people also achieve similar results by deliberately inducing altered states of consciousness. Animistic thinking may emerge in meditation or contemplation, lucid dreaming, from self-hypnosis, when drowsy, in 'trance states' induced by repetitious rhythm or light, or when delirious due to illness, brain injury, psychoses, or intoxication with 'entheogenic' drugs--which is probably one reason for the perennial popularity of inducing intoxicated states. However, intoxication will typically damage memory processes making it harder to learn from any spiritual experiences; and even mild states of cognitive impairment may be dangerous in situations where skilled or responsible behaviour is required. Despite these constraints and limitations, recovering animism through seeking altered states of consciousness could already be considered a major world spiritual practice.

Adult↗
PubMed2005

Roles of the vestibular system in controlling arterial pressure in conscious rats during a short period of microgravity.

In order to evaluate the roles of the vestibular system in controlling arterial pressure (AP) during exposure to a short period of microgravity (microG), the AP was measured in conscious free-moving rats having intact vestibular systems and those having vestibular lesions (FM-Intact and FM-VL groups, respectively). During free drop-induced microG, the AP increased in the FM-Intact group; it was 38+/-4 mmHg more than the AP observed during 1G. However, the increase in AP was significantly lower in the FM-VL group (20+/-2 mmHg). Further, to examine the sudden effect of a body floating in the midair in response to the AP during exposure to muG a body stabilizer was placed on the back of rats having intact vestibular systems and those having vestibular lesions (STAB-Intact and STAB-VL groups, respectively). The increase in the AP was significantly depressed in the STAB-Intact group; when compared with that in the FM-Intact group, but the increase was still significant (27+/-2 mmHg). On the other hand, the increase in the AP was completely eliminated in the STAB-VL group (7+/-5 mmHg). These results indicate that the AP increases during exposure to muG in conscious rats, and the vestibular system and body stability are significantly involved in this response.

Animals↗
PubMed2004

Hemispheric differences between left and right number representations: effects of conscious and unconscious priming.

The contribution of each hemisphere to the generation of number representations was investigated by two lateralized priming experiments in which participants had to compare Arabic digits to a fixed standard of four. In Experiment 1, unmasked primes (Arabic digits or word numerals) were used. In Experiment 2, masked primes were presented consciously or subconsciously. In both experiments similar priming effects were found in the left (LH) and the right hemisphere (RH) when the prime was presented consciously. However, asymmetries emerged when the primes were presented subconsciously: while the priming effects of digits and word numbers were equally large in the right visual half field (RVF-LH), the influence of the word prime on the semantic and the response stage of the left visual half field (LVF-RH) was absent, indicating that a word prime was no longer processed when it was presented subconsciously in LVF-RH. We believe that the origin of the latter effect can be attributed to a failure to transfer word number primes from the RH to the LH when attentional resources are restricted.

Adult↗
PubMed2003

Electrical properties affecting discharge of units of the mid and posterolateral thalamus of conscious cats.

Discharge properties in response to intracellularly applied, rectangular currents were measured in units of the mid (lateralis dorsalis and centrolateral nuclei) and posterolateral (lateralis posterior and pulvinar nuclei) thalamus of conscious cats. A separate aim was to determine if neuronal excitability changed in association with changes in stimulus-evoked activity after the animals were trained to discriminate between two acoustic stimuli when performing a conditioned motor response. Low threshold spike (l.t.s.) discharges were observed in three of 272 cells given 1 nA intracellular, hyperpolarizing current pulses of 40 ms duration. This finding supports the view that thalamic neurons of conscious animals operate mainly in the relay as opposed to the oscillatory mode. Application of larger and longer hyperpolarizing currents in the cells produced rebound l.t.s. discharges, supporting the expectation that most thalamic neurons are capable of producing this type of discharge. Decrements of spike afterhyperpolarizations (AHP) and broadening of spike bases upon repeated discharge also were observed in each area of the thalamus studied. After conditioning, changes were found in the posterolateral thalamus (but not in the mid-thalamus) in the proportions of cells with spontaneous, rapid (>/=50 Hz), repetitive, discharges (RRD) and rapid, sustained discharges at rates >/=100 Hz during application of depolarizing current (RSD). In the posterolateral thalamus the percentage of units responding to 1 nA depolarization with RSD fell from 71% before conditioning to 45% after conditioning. The percentage of cells with RRD decreased from 69% to 46%. The changes were accompanied by a 3 mV hyperpolarization of the membrane potentials of the cells and a decrease in baseline activity. After conditioning, increases in excitability were found in cells of the mid thalamus that responded selectively to the click conditioned stimulus (CS) that elicited the conditioned response, and decreases in excitability were found in cells of the posterolateral thalamus that responded to the discriminative acoustic stimulus (DS) to which the animals were trained not to respond. An earlier study showed a potentiation of discharge in response to the CS in units of the midthalamus after similar conditioning and a reduction of the proportion of DS responsive units and peak discharge to the DS in units of the posterolateral thalamus. We conclude that the discharge properties of units of the mid and posterolateral thalamus can change to support discrimination between acoustic stimuli of different functional significance after conditioning.

Acoustic Stimulation↗
PubMed2004

Central neurogenic hyperventilation in a conscious child associated with glioblastoma multiforme.

Central neurogenic hyperventilation refers to progressive tachypnea leading to hypocarbia and respiratory alkalosis caused by cortical disorders, initially reported in comatose patients with mainly pontine infarction. Central neurogenic hyperventilation in conscious patients is even rarer, numbering around 30 reported cases including seven children, mainly associated with infiltrative gliomas and lymphomas of the brainstem and pons. We report the evolution of central neurogenic hyperventilation in a conscious child associated with an infiltrative glioblastoma multiforme diagnosed 1 year before admission. He presented with progressive tachypnea and dyspnea of 1 week duration. On examination he was fully alert and aware of his respiratory disorder. Respiratory rate was 56 breaths per minute using accessory respiratory muscles. Hyperventilation was unchanged during sleep. Arterial blood gases disclosed marked hypocarbia: Pco(2) of 8 mm Hg resulting in severe respiratory alkalosis at pH of 7.8. Central neurogenic hyperventilation was therefore suggested after exclusion of other respiratory or cardiac disorders. The exaggerated tachypnea persisted along with respiratory alkalosis. Over a period of 2 months his overall state markedly deteriorated; he lapsed into coma, and finally succumbed after involvement of medullary cardiovascular centers. Although extremely rare in the pediatric age group, central neurogenic hyperventilation should be suspected in any alert child presenting with unexplained increasing tachypnea and hypocarbia leading to respiratory alkalosis. The evolution of such a disorder may be an alarming sign of ensuing deterioration in patients with tumors of the brainstem and medulla before cardiovascular derangement.

Alkalosis, Respiratory↗