Current research on the neural basis of consciousness is based mainly on neuroimaging, physiology and psychophysics. This target article reviews what is known about biochemical factors that may contribute to the development of consciousness, based on loss of consciousness (i.e., coma). There are two theories of the biochemical mode of action of general anaesthetics. One is that anaesthesia is a direct (i.e., not receptor-mediated) effect of the anaesthetic on cellular neurophysiological function; the other is that some alteration of receptor function (...) occurs. General anaesthetics are mainly GABA agonists but some (such as ketamine) are glutamate antagonists. They also affect other systems, particularly cholinergic ones. There are various comas of metabolic origin. For example, a combination of small doses of the iron chelators desferrioxamine and prochlorperazine induce a profound and long lasting coma in humans. The mechanisms that might mediate this include redox mechanisms at the glutamate synapse, post-synaptic endocytosis of dopamine and iron, and intracellular iron-dopamine complexes, which are powerful dismuters of the superoxide anion. New findings in cell biology relating to endocytosis and recycling of receptors are discussed in a wider context. These biochemical events may induce coma by two mechanisms: (i) Consciousness may depend on widespread cortical (or cortico-thalamic) activation. (ii) Whereas these biochemical changes are widespread, only the changes in a subset of consciousness' neurons may count. An experimental program to distinguish between these two alternatives is proposed. (shrink)
Following coma, some patients will recover wakefulness without signs of consciousness (only showing reflex movements, i.e., the vegetative state) or may show non-reflex movements but remain without functional communication (i.e., the minimally conscious state). Currently, there remains a high rate of misdiagnosis of the vegetative state (Schnakers et. al. BMC Neurol, 9:35, 8) and the clinical and electrophysiological markers of outcome from the vegetative and minimally conscious states remain unsatisfactory. This should incite clinicians to use multimodal assessment to detect objective (...) signs of consciousness and validate para-clinical prognostic markers in these challenging patients. This review will focus on advanced magnetic resonance imaging (MRI) techniques such as magnetic resonance spectroscopy, diffusion tensor imaging, and functional MRI (fMRI studies in both “activation” and “resting state” conditions) that were recently introduced in the assessment of patients with.. (shrink)
Detecting conscious awareness in a patient emerging from a coma state is problematic, because our standard attributions of conscious awareness rely on interpreting bodily movement as intentional action. Where there is an absence of intentional bodily action, as in the vegetative state, can we reliably assume that there is an absence of conscious awareness? Recent neuroimaging work suggests that we can attribute conscious awareness to some patients in a vegetative state by interpreting their brain activity as intentional mental action. I (...) suggest that this change of focus, from the interpretation of motor behaviour as intentional bodily action to the interpretation of neural activity as intentional mental action, raises philosophical issues that affect the interpretation of the neuroimaging data. (shrink)
In this article I contend that the tendency to equate coma with anencephalia is a mistake. A key idea here is that there is a type of "mental-state" predicate that is applicable to the comatose but not to anencephalics. One of the moral implications of this is that the concept of "brain death", its alleged popularity notwithstanding, is badly confused. Also, because anencephalics have no mental life, there are few moral grounds for hesitating to use anencephalics as organ donors.
Herbert, Michael Clinicians are beginning to understand the varied outcomes following severe brain injury, one of which is post-coma unresponsiveness (PCU). However, much still needs to be done to fully comprehend this elusive state. Current clinical knowledge is outlined below.
McGovern, Kevin This article reviews three statements from the National Health and Medical Research Council on post-coma unresponsiveness (PCU). One of the functions of the NHMRC is to propose standards and guidelines for health care in Australia. The paper explores the causes and neuropathology of PCU, imaging and other tests and prognosis from unresponsiveness.
In order to better understand the functional contribution of resting state activity to conscious cognition, we aimed to review increases and decreases in fMRI functional connectivity under physiological (sleep), pharmacological (anesthesia) and pathological altered states of consciousness, such as brain death, coma, vegetative state/unresponsive wakefulness syndrome, and minimally conscious state. The reviewed RSNs were the DMN, left and right executive control, salience, sensorimotor, auditory and visual networks. We highlight some methodological issues concerning resting state analyses in severely injured brains mainly (...) in terms of hypothesis-driven seed-based correlation analysis and data-driven independent components analysis approaches. Finally, we attempt to contextualize our discussion within theoretical frameworks of conscious processes. We think that this “lesion” approach allows us to better determine the necessary conditions under which normal conscious cognition takes place. At the clinical level, we acknowledge the technical merits of the resting state paradigm. Indeed, fast and easy acquisitions are preferable to activation paradigms in clinical populations. Finally, we emphasize the need to validate the diagnostic and prognostic value of fMRI resting state measurements in non-communicating brain damaged patients. (shrink)
In this paper, the incidental clauses delimited by commas are inquired from a computational linguistic perspective. Some theoretical aspects based on grammatical criteria, and a discussion about its nature and definition are proposed. For this objective, we consider (i) the possibility that incidental clause has (or not) a syntactic function, (ii) the possibility that the incidental clauses interrupts (or not) the regular order of the sentence where it is inserted, and (iii) the different levels where the incidental clauses could be (...) situated. From these issues, a classification and a definition of incidental clauses delimited by commas are proposed, and a method for automatic detection of these expressions using the Smorph and MPS softwares are described; this method got adequate accuracy and coverage percentages. Finally the contribution of this paper for the grammatical studies and the computational linguistics are presented, and new topics for future works are proposed. (shrink)
The prospect, in terms of subjective expectations, of immortality under the no-collapse interpretation of quantum mechanics is certain, as pointed out by several authors, both physicists and, more recently, philosophers. The argument, known as quantum suicide, or quantum immortality, has received some critical discussion, but there hasn't been any questioning of David Lewis's point that there is a terrifying corollary to the argument, namely, that we should expect to live forever in a crippled, more and more damaged state, that barely (...) sustains life. This is the prospect of eternal quantum torment. Based on some empirical facts, I argue for a conclusion that is much more reassuring than Lewis's terrible scenario.1. (shrink)
In the care of patients with disorders of consciousness (DOC), some ethical difficulties stem from the challenges of accurate diagnosis and the uncertainty of prognosis. Current neuroimaging research on these disorders could eventually improve the accuracy of diagnoses and prognoses and therefore change the context of end-of-life decision making. However, the perspective of healthcare professionals on these disorders remains poorly understood and may constitute an obstacle to the integration of research. We conducted a qualitative study involving healthcare professionals from an (...) acute care university medical center. A short questionnaire captured demographic data as well as the experience of participants with DOC patients. A semi-structured interview was used to explore attitudes toward ethical issues identified in a previous literature review. Qualitative content analysis of interviews was conducted with the NVivo software. Accurate diagnosis among DOC is often regarded as a challenge, but this was generally not the case for our participants because most reported high confidence in DOC diagnoses. However, participants reported struggling with prognosis, especially because of its essential role for end-of-life decision making and communication with families. Variability of opinion between healthcare professionals was reported and identified by some as a minor issue while others stressed how families struggle with different medical opinions. End-of-life decision making encompassed a large proportion of ethical challenges in these patients, and the removal of artificial nutrition and hydration created significant discomfort in a minority of participants. The concept of futility was subject to wide-ranging understandings with both favorable and unfavorable opinions. Our data suggest that to ensure the incorporation of new evidence-based advances, attention should be directed to the real-world practices and challenges of accurate diagnosis and prognosis. Given pervasive challenges in end-of-life care, we recommend improved training of healthcare professionals in the care of patients with DOC, particularly in end-of life care, understanding the context of decision making, and determining how to optimally integrate new neuroscience research on the care of patients with DOC. (shrink)
A global workspace is a hub of binding and propagation in a population of loosely coupled signaling elements. Global workspace (GW) architectures recruit many distributed, specialized agents to help resolve focal ambiguities. In the brain, conscious experiences may reflect a global workspace function. For animals the natural world is full of fitness-related ambiguities, suggesting a general adaptive pressure for brains to resolve focal ambiguities quickly and accurately. In humans and related species the cortico-thalamic (C-T) core is believed to underlie conscious (...) aspects of perception, thinking, learning, feelings of knowing, emotions, imagery, working memory and executive control. The C-T core has many anatomical hubs, but conscious percepts are unitary and internally consistent at any given moment. The repertoire of conscious contents is a large, open set. These points suggest that a brain-based GW capacity cannot be localized in a single anatomical hub. Rather, it should be sought in a dynamic capacity for adaptive binding and propagation of neural signals over multi-hub networks. We refer to this as dynamic global workspace theory (dGW). In this view, conscious contents can arise in any region of the C-T core when multiple signal streams settle on a winner-take-all equilibrium. The resulting bound gestalt may ignite an any-to-many broadcast, lasting ~100-200 ms, and trigger widespread adaptation in established networks. Binding and broadcasting may involve theta/gamma or alpha/gamma phase coupling. Conscious contents (qualia) may reflect their sources in cortex. Sensory percepts may bind and broadcast from posterior regions, while non-sensory feelings of knowing (FOKs) may be frontotemporal. The small focal capacity of conscious contents may be the biological price to pay for global access. We propose that in the intact brain the hippocampal/rhinal complex may support conscious event organization as well as episodic memory coding. (shrink)
Notwithstanding fundamental methodological advancements, scientific information about disorders of consciousness (DOCs)—e.g. Vegetative State/Unresponsive Wakefulness Syndrome (VS/UWS) and Minimally Conscious State (MCS)—is incomplete. The possibility to discriminate between different levels of consciousness in DOC states entails treatment strategies and ethical concerns. Here we attempted to investigate Italian clinicians’ and basic scientists’ opinions regarding some issues emerging from the care and the research on patients with DOCs. From our survey emerged that Italian physicians working with patients with DOCs give a central role (...) to ethics. Current Italian regulation regarding basic research conducted in patients with DOCs apparently risks to be inadequate to support scientific advancement, and would deserve a different assessment compared to ordinary treatments. We think the results of our survey deserve attention from an international audience because they exemplify the difficulty to define a shared approach to the issues related to patients with DOCs and the necessity to better assess both the ordinary and experimental treatment of patients with DOCs at the ethical and legal level. (shrink)
The case of Terri Schiavo, a young woman who spent 15 years in a persistent vegetative state, has emerged as a watershed in debates over end-of-life care. While many observers had thought the right to refuse medical treatment was well established, this case split a family, divided a nation, and counfounded physicians, legislators, and many of the people they treated or represented. In renewing debates over the importance of advance directives, the appropriate role of artificial hydration and nutrition, and the (...) responsibilities of family members, the case also became one of history's most extensively litigated health care disputes. The Case of Terri Schiavo assembles a team of first-hand participants and content experts to provide thoughtful and nuanced analyses. In addition to a comprehensive overview, the book includes contributions by Ms. Schiavo's guardian ad litem, a neurologist and lawyer who participated in the case, and scholars who examine issues related to litigation, faith, gender, and disability. The volume also includes a powerful dissent from the views of many scholars in the bioethics community. The book is intended for students, health care professionals, policy makers, and other in search of carefully reasoned analyses of the case that will shape our view of death and end-of-life medical care for decades. (shrink)
Zum Hirntod werden zwei Fragen erneut kontrovers diskutiert: erstens, ob der Hirntod mit dem Tod gleichzusetzen ist, zweitens, wie man den Hirntod sicher diagnostiziert. Neue empirische Erkenntnisse erfordern eine neue Auseinandersetzung mit diesen Fragen: Erstens haben zahlreiche Studien ein längeres Überleben und die Integration von Körperfunktionen von hirntoten Patienten nachgewiesen. Der President's Council on Bioethics hat im Dezember 2008 eingestanden, dass die bisher vertretene Begründung für das Hirntodkriterium, nämlich die Annahme des engen zeitlichen und kausalen Zusammenhangs des Hirntodes und der (...) Desintegration der körperlichen Funktionen, empirisch widerlegt sei. Trotzdem hält der Council am Hirntodkriterium fest, stützt es aber nun auf eine neue naturphilosophische statt empirische Begründung, die den lebenden Organismus über die aktive Auseinandersetzung mit der Welt als notwendiges Kriterium für Leben bestimmt. Diese naturphilosophische Begründung ist nicht falsifizierbar und scheint den Interessen der Transplantationsmedizin geschuldet. Zweitens geben Studien mit fMRT und PET an hirntoten Patienten Anlass, an der Reliabilität der üblichen Hirntoddiagnostik zu zweifeln. Aus ethischen Gründen sollte eine Hirntoddiagnostik auf dem Stand der besten verfügbaren Technologie gesetzlich vorgeschrieben werden, also zumindest die Angiographie, in Zweifelsfällen auch fMRT oder PET. (shrink)
Einhergehend mit den Fortschritten in der Reanimationsmedizin beschäftigen sich seit den 80er Jahren viele Studien mit der prognostischen Güte von reanimations- und patientenbezogenen Akutmarkern. Generell sollen Prognosemarker die Vorhersagbarkeit des Heilungspotenzials erlauben, sie besitzen dadurch eine Steuerfunktion für das weitere Therapiekonzept. Die Wertigkeit dieser Prädiktoren verändert sich jedoch, wenn sie als Determinanten bei Non-Treatment-Entscheidungen herangezogen werden. Dies aus zwei Gründen: 1. Nach Sichtung der Literatur und eingedenk eigener Studienresultate fehlt bislang ein 100%- sicherer Prognose-Algorithmus für Patienten im posthypoxischen Koma. 2. (...) Der komatöse Patient kann an der Beurteilung der Prognoseaussagen selbst nicht teilnehmen. Es stellt sich somit die Frage: Dürfen Prognosemarker unser moralisches Handeln an der Grenze des Lebens leiten? Die Autoren bejahen diese Frage und sehen eine adäquat moralische Handlungsoption in der Durchführung einer diskurs-pragmatischen Patientenkonferenz. Den Prognosemarkern kommt hier eine Stellvertreterfunktion im Sinne eines „stillen Patientenargumentes“ zu, wodurch die potenzielle Dialogfähigkeit des Patienten als moralisches Anspruchsobjekt gewahrt wird. Im Rahmen einer diskursiven Erörterung wird dann der Einfluss der Prognosedaten an der Entscheidung gewichtet. (shrink)
One reason why the Biological Approach to personal identity is attractive is that it doesn’t make its advocates deny that they were each once a mindless fetus.[i] According to the Biological Approach, we are essentially organisms and exist as long as certain life processes continue. Since the Psychological Account of personal identity posits some mental traits as essential to our persistence, not only does it follow that we could not survive in a permanently vegetative state or irreversible coma, but it (...) would appear that none of us was ever a mindless fetus. But what happens to the organism that was a mindless fetus when the _person_ arrives on the scene?[ii] Can the acquisition of thought destroy an organism? That would certainly be news to biologists. Does one organism cease to exist with the emergence of thought and another organism, one identical to the person, take its place? (Burke,1994) That doesn’t seem much more plausible than the previous move. Should identity and Leibniz. (shrink)