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PubMed2003

Changes in MRI signal intensity during hypercapnic challenge under conscious and anesthetized conditions.

Most functional magnetic resonance imaging (fMRI) studies in animals are conducted under anesthesia to minimize motion artifacts. However, methods and techniques have been developed recently for imaging fully conscious rats. Functional MRI studies on conscious animals report enhanced BOLD signal changes as compared to the anesthetized condition. In this study, rats were exposed to different concentrations of carbon dioxide (CO(2)) while conscious and anesthetized to test whether cerebrovascular reactivity may be contributing to these enhanced BOLD signal changes. Hypercapnia produced significantly greater increases in MRI signal intensity in fully conscious animals (6.7-13.3% changes) as when anesthetized with 1% isoflurane (3.2-4.9% changes). In addition, the response to hypercapnia was more immediate in the conscious condition (< 30s) with signal risetimes twice as fast as in the anesthetized state (60s). Both cortical and subcortical brain regions showed a robust, dose- dependent increase in MRI signal intensity with hypercapnic challenge while the animals were conscious but little or no change when anesthetized. Baseline variations in MRI signal were higher while animals were conscious but this was off set by greater signal intensity changes leading to a greater contrast-to-noise ratio, 13.1 in conscious animals, as compared to 8.0 in the anesthetized condition. In summary, cerebral vasculature appears to be more sensitive to hypercapnic challenge in the conscious condition resulting in enhanced T2* MRI signal intensity and the potential for better BOLD signal changes during functional imaging.

Anesthesia↗
PubMed1998

Investigating the biology of consciousness.

The fact that consciousness is a private, first-person phenomenon makes it more difficult to study than other cognitive phenomena that, although being equally private, also have characteristic behavioural signatures. Nonetheless, by combining cognitive and neurobiological methods, it is possible to approach consciousness, to describe its cognitive nature, its behavioural correlates, its possible evolutionary origin and functional role; last but not least, it is possible to investigate its neuroanatomical and neurophysiological underpinnings. In this brief essay I distinguish between two kinds of consciousness: core consciousness and extended consciousness. Core consciousness corresponds to the transient process that is incessantly generated relative to any object with which an organism interacts, and during which a transient core self and transient sense of knowing are automatically generated. Core consciousness requires neither language nor working memory, and needs only a brief short-term memory. Extended consciousness is a more complex process. It depends on the gradual build-up of an autobiographical self, a set of conceptual memories pertaining to both past and anticipated experiences of an individual, and it requires conventional memory. Extended consciousness is enhanced by language.

Biological Evolution↗
PubMed1983

The effects of apomorphine upon local cerebral glucose utilization in conscious rats and in rats anesthetized with chloral hydrate.

The effects of the dopaminergic agonist apomorphine (1 mg . kg-1 i.v.) upon local cerebral glucose utilization in 43 anatomically discrete regions of the CNS were examined in conscious, lightly restrained rats and in rats anesthetized with chloral hydrate by means of the quantitative autoradiographic [14C]2-deoxyglucose technique. In animals anesthetized with chloral hydrate, glucose utilization was reduced throughout all regions of the CNS from the levels observed in conscious animals, although the magnitude of the reductions in glucose use displayed considerable regional heterogeneity. With chloral hydrate anesthesia, the proportionately most marked reductions in glucose use (by 40-60% from conscious levels) were noted in primary auditory nuclei, thalmaic relay nuclei, and neocortex, and the least pronounced reductions in glucose use (by 15-25% from conscious levels) were observed in limbic areas, some motor relay nuclei, and white matter. In conscious, lightly restrained rats, the administration of apomorphine (1 mg . kg-1) effected significant increased in glucose utilization in 15 regions of the CNS (e.g., subthalamic nucleus, ventral thalamic nucleus, rostral neocortex, substantia nigra, pars reticulata), and significant reductions in glucose utilization in two regions of the CNS (lateral habenular nucleus and anterior cingulate cortex). In rats anesthetized with chloral hydrate, the effects of apomorphine upon local glucose utilization were less widespread and less marked than in conscious animals. In only two of the regions (the globus pallidus and septal nucleus), which displayed increased glucose use following apomorphine in conscious rats, were significant increases in local glucose utilization observed with this agent in chloral hydrate-anesthetized rats. In the pars compacta of the substantia nigra, in which apomorphine increased glucose utilization in conscious animals, significant reductions in glucose utilization were observed following apomorphine in rats anesthetized with chloral hydrate. The profound effects of chloral hydrate anesthesia upon local cerebral glucose use, and the modification by this anesthetic regime of the local metabolic responses to apomorphine, emphasize the difficulties which exists in the extrapolation of data from anesthetized animals to the conditions which prevail in the conscious animal.

Animals↗
PubMed2003

Making sense of self-conscious emotion: linking theory of mind and emotion in children with autism.

Self-conscious emotions such as embarrassment and shame are associated with 2 aspects of theory of mind (ToM): (a) the ability to understand that behavior has social consequences in the eyes of others and (b) an understanding of social norms violations. The present study aimed to link ToM with the recognition of self-conscious emotion. Children with and without autism identified facial expressions conscious of self-conscious and non-self-conscious emotions from photographs. ToM was also measured. Children with autism performed more poorly than comparison children at identifying self-conscious emotions, though they did not differ in the recognition of non-self-conscious emotions. When ToM ability was statistically controlled, group differences in the recognition of self-conscious emotion disappeared. Discussion focused on the links between ToM and self-conscious emotion.

Adolescent↗
PubMed1998

Blindsight and shape perception: deficit of visual consciousness or of visual function?

Two people with homonymous right hemianopias were tested on a number of measures of non-conscious and conscious perception of shape in the blind field. Experiment 1 examined preparatory manual adjustments in grasping objects. Both subjects performed well above chance not only in three-dimensional location but also in preforming the hand to the shape, size and orientation of objects. In Experiment 2 single upper-case letters were briefly exposed in the blind field, and subjects made forced choices among 6 alternatives in the sighted field. Performance improved over blocks of trials and was above chance, but not dramatically. In Experiment 3 single upper-case words were briefly presented in the blind field, and subjects chose which of two words exposed after in the intact field was semantically closer. In Experiment 4 subjects had to give the meaning of single ambiguous words (e.g. BANK) presented both visually in the intact field and auditorily. Each ambiguous word was preceded by a single upper-case word briefly presented in the blind field, biasing each meaning on different blocks of trials (e.g. MONEY and RIVER). In Experiment 3, although results were in the appropriate direction, they were not consistently well above chance. By contrast, in Experiment 4 both subjects were consistently semantically biased to a high degree by words in the blind field. Experiments 2, 3 and 4 taken together suggest that indirect techniques (priming) are more sensitive to showing effects of non-conscious perception than direct ones (forced-choice). More importantly the experiments indicate that not only orientation but curvature, structural descriptions of component strokes and spatial ordering of letters are registered non-consciously in the blind field. Experiment 5 examined after-images in the blind and sighted fields, showing veridical conscious perception of shape in the blind field provided it was accompanied by a shape in the sighted field which together formed a good Gestalt. Experiment 6 showed conscious perception of illusory contours spanning the hemifields induced by Kanizsa figures. The experiments suggest that aspects of shape are much better perceived in blindsight than previously thought, that this is independent of their use in motor control, that the main deficit in blindsight is one of consciousness, and that the loss of conscious vision in the blind field is far from total. The effects and their relationship to those in other neuropsychological deficits suggest an intimate link between perceptual consciousness, attention and object perception.

Afterimage↗
PubMed1999

Ketamine preserves and propofol potentiates hypoxic pulmonary vasoconstriction compared with the conscious state in chronically instrumented dogs.

BACKGROUND: The authors tested the hypothesis that ketamine and propofol anesthesia would alter the magnitude of hypoxic pulmonary vasoconstriction compared with the conscious state. In addition, they assessed the extent to which cyclooxygenase pathway inhibition and adenosine triphosphate-sensitive potassium channel inhibition modulate hypoxic pulmonary vasoconstriction in the conscious state, and whether these pathways are altered during propofol anesthesia. METHODS: Twenty conditioned, male mongrel dogs were chronically instrumented to measure the left pulmonary vascular pressure-flow relationship. Pressure-flow plots were measured during normoxia and hypoxia (systemic arterial PO2 reduced to about 60 and about 50 mm Hg) on separate days in the conscious state, during ketamine anesthesia, and during propofol anesthesia. The effects of indomethacin and glibenclamide on the magnitude of hypoxic pulmonary vasoconstriction were also assessed in the conscious and propofol-anesthetized states. RESULTS: Neither ketamine nor propofol had an effect on the baseline pressure-flow relationship during normoxia compared with the conscious state. Hypoxia resulted in stimulus-dependent pulmonary vasoconstriction (P<0.01) in the conscious state. Compared with the conscious state, the magnitude of hypoxic pulmonary vasoconstriction was preserved during ketamine but was potentiated (P<0.01) during propofol anesthesia. Indomethacin enhanced (P<0.01) hypoxic pulmonary vasoconstriction in both the conscious and propofol-anesthetized states. In contrast, glibenclamide only enhanced (P<0.01) hypoxic pulmonary vasoconstriction in the conscious state and had no effect during propofol anesthesia. CONCLUSION: Hypoxic pulmonary vasoconstriction is preserved during ketamine anesthesia but is potentiated during propofol anesthesia. The potentiated response during propofol anesthesia appears to be caused by inhibition of adenosine triphosphate-sensitive potassium channel-mediated pulmonary vasodilation.

Anesthetics, Dissociative↗
PubMed1999

Optimization of conscious sedation in plastic surgery.

The administration of conscious sedation by the plastic surgeon must be safe, efficient, and consistent. In the proper setting, with trained staff and appropriate backup, conscious sedation can allow optimal patient satisfaction with expedient recovery in addition to cost containment. The highly effective local anesthesia afforded by dilute, high-volume ("tumescent") infiltration extends the use of conscious sedation to cases previously performed under general anesthesia or deep sedation. The purpose of this analysis was to identify variables in conscious sedation that affect traditional outcome parameters in ambulatory surgery, particularly the duration of recovery and adverse events such as nausea and emesis. All perioperative and operative records of 300 consecutive patients having plastic surgical procedures under conscious sedation were carefully reviewed. Patients were ASA class I or II by requisite. Conscious sedation followed a standardized administration protocol, using incremental doses of two agents: midazolam (0.25 to 1 mg) and fentanyl (12.5 to 50 mcg). A subset of patients received preoperative oral sedation. Multivariate statistical analysis was conducted using SPSS 8.0 for Windows (SPSS Inc., Chicago, Ill.). Of the 300 patients, same-day discharge was intended for 281. Eight procedure categories were defined. No anesthetic complications occurred. As expected, recovery time was significantly correlated with the duration and type of procedure (p < 0.001) and the total dosage of both intraoperative sedative agents (p < 0.001). Interestingly, a negative correlation with advancing age existed (p < 0.001), likely reflecting the significantly higher intraoperative sedative dosing in younger patients (p < 0.001). When controlled for the effects of procedure duration and intraoperative sedative dosing, two other variables-use of preoperative oral sedation and postoperative nausea/emesis-significantly lengthened recovery time (p = 0.0001 for each). Fifteen unintended admissions occurred secondary to nausea, prolonged drowsiness, or pain control needs. Conscious sedation is an effective anesthetic choice for routine plastic surgical procedures, many of which would commonly be performed under general anesthesia. In our experience with a carefully structured and controlled conscious sedation protocol, the technique has proven to be safe and effective. This analysis of outcome parameters identified two important and potentially avoidable causes of recovery delay following conscious sedation-oral premedication and nausea/emesis. Nausea and emesis were particularly problematic in that they were responsible for 11 of 15 (73 percent) unintended admissions. Preoperative sedation is valuable in certain circumstances, and its use is not discouraged; however, its benefits must be weighed against its unwanted effects, which can include a prolongation of recovery.

Adolescent↗
PubMed2003

Why do seizures cause loss of consciousness?

Model systems are needed for the scientific investigation of consciousness. A good model system should include variable states of consciousness, allowing the relationship between brain activity and consciousness to be investigated. Examples include sleep, anesthesia, focal brain lesions, development, evolution, and epilepsy. One advantage of epilepsy is that changes are dynamic and rapidly reversible. The authors review previous investigations of impaired consciousness in epilepsy and describe new findings that may shed light on both normal and abnormal mechanisms of consciousness. Abnormal increased activity in fronto-parietal association cortex and related subcortical structures is associated with loss of consciousness in generalized seizures. Abnormal decreased activity in these same networks may cause loss of consciousness in complex partial seizures. Thus, abnormally increased or decreased activity in the same networks can cause loss of consciousness. Information flow during normal conscious processing may require a dynamic balance between these two extremes of excitation and inhibition.

Animals↗
PubMed1986

Effects of nimodipine on cerebral blood flow in conscious rat.

The purpose of this study was to determine the effects of the calcium channel blocker nimodipine (NM) on cerebral blood flow in the rat under conscious and anesthesized conditions and to compare these to effects of the drug in other circulations. Regional blood flows were measured using the radioactive microsphere technique. Hemodynamic parameters were assessed at the time of blood flow determinations in conscious rats and in pentobarbital-anesthetized rats. NM was administered i.v. using a cumulative dosing regimen in conscious (6, 24 and 60 micrograms/kg) and anesthetized (6 and 60 micrograms/kg) rats. In conscious rats, NM dose-dependently increased coronary blood flow whereas significantly lowering pressure-rate product and slightly but significantly reduced mean arterial pressure and systemic vascular resistance. In conscious rats, NM had no significant effect on cerebral blood flow or cerebral vascular resistance. In anesthetized rats, cerebral and systemic vascular resistances were higher compared to conscious animals. In anesthetized animals, NM reduced mean arterial pressure and systemic resistance to a greater extent than in conscious rats and significantly increased cerebral blood flow. Base-line coronary resistance was similar in conscious and anesthetized rats and the coronary dilator effects of NM were also similar under the two conditions. These findings suggest that NM is not a selective cerebral vasodilator in rats and that the cerebral dilator effects of this drug are not apparent in conscious rats. Only under the high cerebral resistance condition induced by pentobarbital anesthesia was NM found to be a cerebral vasodilator in the rat.

Anesthesia↗
PubMed2004

Early impairment in consciousness predicts mortality after hemispheric ischemic stroke.

OBJECTIVE: Early predictors of poor outcome after acute ischemic stroke may be useful in selecting patients for potentially beneficial but high-risk interventions. DESIGN: Cohort study of patients given placebo in a randomized clinical trial. SETTING: Multicenter trial at 139 U.S. and 14 Canadian hospitals. PATIENTS: A cohort of 564 placebo-treated patients with major anterior circulation ischemic stroke enrolled in the Clomethiazole in Acute Stroke Study-Ischemic Stroke (CLASS-I) trial. Patients did not have significant impairment in consciousness at baseline and were enrolled within 12 hrs of symptom onset. INTERVENTIONS: Prospective data collection of a number of clinical variables including use of a 6-point level of consciousness scale (1 = awake, 6 = no reaction to pain) to measure patients' level of consciousness at enrollment and 12 additional times during the first 24 hrs after enrollment. The ability of level of consciousness score and additional clinical data to predict 30-day mortality was assessed. MEASUREMENTS AND MAIN RESULTS: At 1 month, 114 of 564 patients (20%) had died. In univariate analysis, factors significantly associated with mortality included older age, white race, higher National Institutes of Health Stroke Scale score, higher serum glucose, atrial fibrillation, and any impairment in level of consciousness (p <.05). After controlling for these factors, increasing level of consciousness score at 3 hrs after enrollment and at all but one subsequent time point was significantly associated with increased mortality (odds ratio, 1.8 per point; 95% confidence interval, 1.2-2.6; p =.003 at 3-hr time point). Maximum level of consciousness score during the initial 24 hrs of monitoring also predicted mortality (odds ratio, 1.9 per point; 95% confidence interval, 1.4-2.5; p <.001). CONCLUSION: The development of a decreased level of consciousness within the initial hours after stroke onset, as evaluated by a simple six-point scale, is a powerful independent predictor of mortality after major anterior circulation ischemic stroke.

Age Distribution↗
PubMed2004

[How often does decreased consciousness of hypoglycaemia occur in children and adolescents with diabetes type 1 and what are its consequences?].

UNLABELLED: The inability of the patient to recognize the risk of hypoglycemia is a very frequent phenomenon, but it is also often an underestimated complication in diabetes treated with insulin. The results of DCCT trial revealed that intensification in insulin therapy increases three-fold the risk of severe hypoglycaemia. Feeling the state of hypoglycaemia is the basic defensive mechanism in patients with diabetes type 1, making possible to start the self treatment. The decreased consciousness of hypoglycaemia makes limitations to intensive insulin therapy, which main aim is to stop later complications. THE AIM OF THE STUDY was to answer the questions: 1. How often does lack of consciousness of hypoglycaemia occur in children and adolescents with diabetes type 1. 2. What are the possible factors influencing appearance of hypoglycaemia. 3. Is lack of hypoglycaemia consciousness of a risk factor for severe hypoglycaemia. MATERIAL AND METHODS: The study was carried out on 318 patients aged x=13.6 yrs (4-21), suffering from diabetes, mean 6.6 yrs (2-18). The study was retrospective taking into consideration the period from 1.01.1998 to 31.12.2002. RESULTS: In the analysis of the questionnaire assessing the occurrence of hypoglycaemia it was found that 82 patients (25.8%) have problems with feeling the state of hypoglycaemia. We analyzed the influence of time of lasting diabetes and we found that patients with a longer duration of the disease more frequently have problems with feeling hypoglycaemia, 57% patients with lack of hypoglycaemia consciousness have bad metabolic control of the disease. In the analyzed period, 64 incidences of severe hypoglycaemia in 48 patients (30 boys and 18 girls) were found. In patients with lack of consciousness of feeling hypoglycaemia the incidences of severe hypoglycaemia occurred ten times more frequently compared to patients who feel hypoglycaemia. Sleeping makes it impossible to perceive early symptoms of hypoglycaemia: in our patients 51 severe incidences (79.7%) occurred at 1.00-3.00 a.m., 6 (9.3%) occurred at daybreak and 7 (11%) in the evening. CONCLUSIONS: 1. In patients with diabetes type 1 the lack of hypoglycaemia consciousness occurs in about 25%. 2. The lack of hypoglycaemia consciousness is closely connected with time of diabetes duration and with recurrence of hypoglycaemia incidences. 3. Patients with lack of hypoglycaemia consciousness are at greater risk for severe hypoglycemia.

Adolescent↗
PubMed1996

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

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

Ambulatory Surgical Procedures↗
PubMed2005

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

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

Animals↗
PubMed1998

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

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

Consciousness↗
PubMed1999

Binding and the phenomenal unity of consciousness.

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

Awareness↗
PubMed1995

Cerebral bases of consciousness: a historical view.

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

Alcohol Amnestic Disorder↗
PubMed1994

EEG detection of nontonic-clonic status epilepticus in patients with altered consciousness.

Subtypes of status epilepticus (SE) without tonic-clonic convulsions (nontonic-clonic SE) present as altered consciousness sometimes with subtle motor activity and are important to consider in the differential diagnosis of patients with unexplained altered consciousness. Other patients may have altered consciousness with intermittent ictal activity on electroencephalography (EEG) that represents probable SE, but have other medical conditions that may be contributing to altered consciousness. EEG is the only reliable way to make the diagnosis of nontonic-clonic SE and we make emergency EEG available on a 24-h basis at our hospital. To determine how often definite or probable nontonic-clonic SE was detected by EEG we prospectively collected data on all cases where physicians ordered EEG to evaluate altered consciousness or possible SE. Out of 198 cases with altered consciousness but no clinical convulsions, 74 (37%) showed EEG and clinical evidence of definite or probable nontonic-clonic SE. Forty-two episodes (57%) were probable or definite complex partial SE, 29 (39%) were probable or definite subtle generalized SE, and three (4%) were myoclonic SE. In 23 SE cases altered consciousness was the only clinical sign at the time of diagnosis; subtle motor activity was present in 36 others. Neither clinical signs nor prior history predicted which patients showed SE on EEG. Nontonic-clonic SE followed a cerebral infarction in 16 cases. Contrary to other reports, we found no relationship between duration of SE and EEG pattern. Subtle generalized SE occurred most commonly in the setting of a diffuse brain injury rather than evolving from convulsive SE. This study demonstrates that nontonic-clonic SE is a common finding in patients with unexplained altered consciousness and EEG is necessary in the evaluation of these patients.

Adolescent↗
PubMed2005

Single-neuron theory of consciousness.

By most accounts, the mind arises from the integrated activity of large populations of neurons distributed across multiple brain regions. A contrasting model is presented in the present paper that places the mind/brain interface not at the whole brain level but at the level of single neurons. Specifically, it is proposed that each neuron in the nervous system is independently conscious, with conscious content corresponding to the spatial pattern of a portion of that neuron's dendritic electrical activity. For most neurons, such as those in the hypothalamus or posterior sensory cortices, the conscious activity would be assumed to be simple and unable to directly affect the organism's macroscopic conscious behavior. For a subpopulation of layer 5 pyramidal neurons in the lateral prefrontal cortices, however, an arrangement is proposed to be present such that, at any given moment: (i) the spatial pattern of electrical activity in a portion of the dendritic tree of each neuron in the subpopulation individually manifests a complexity and diversity sufficient to account for the complexity and diversity of conscious experience; (ii) the dendritic trees of the neurons in the subpopulation all contain similar spatial electrical patterns; (iii) the spatial electrical pattern in the dendritic tree of each neuron interacts non-linearly with the remaining ambient dendritic electrical activity to determine the neuron's overall axonal response; (iv) the dendritic spatial pattern is reexpressed at the population level by the spatial pattern exhibited by a synchronously firing subgroup of the conscious neurons, thereby providing a mechanism by which conscious activity at the neuronal level can influence overall behavior. The resulting scheme is one in which conscious behavior appears to be the product of a single macroscopic mind, but is actually the integrated output of a chorus of minds, each associated with a different neuron.

Animals↗