Consciousness as a definition of death: its appeal and complexity

Memories without Survival: Personal Identity and the Ascending Reticular Activating System

Lockean views of personal identity maintain that we are essentially persons who persist diachronically by virtue of being psychologically continuous with our former selves. In this article, I present a novel objection to this variant of psychological accounts, which is based on neurophysiological characteristics of the brain. While the mental states that constitute said psychological continuity reside in the cerebral hemispheres, so that for the former to persist only the upper brain must remain intact, being conscious additionally requires that a structure originating in the brainstem-the ascending reticular activating system-be functional. Hence, there can be situations in which even small brainstem lesions render individuals irreversibly comatose and thus forever preclude access to their mental states, while the neural correlates of the states themselves are retained. In these situations, Lockeans are forced to regard as fulfilled their criterion of diachronic persistence since psychological continuity, as they construe it, is not disrupted. Deeming an entity that is never again going to have any mental experiences to be a person, however, is an untenable position for a psychological account to adopt. In their current form, Lockean views of personal identity are therefore incompatible with human neurophysiology.

Brain Death as the End of a Human Organism as a Self-moving Whole

The biophilosophic justification for the idea that "brain death" (or total brain failure) is death needs to support two claims: (1) that what dies in human death is a human organism, not merely a psychological entity distinct from it; (2) that total brain failure signifies the end of the human organism as a whole. Defenders of brain death typically assume without argument that the first claim is true and argue for the second by defending the "integrative unity" rationale. Yet the integrative unity rationale has fallen on hard times. In this article, I give reasons for why we should think of ourselves as organisms, and why the "fundamental work" rationale put forward by the 2008 President's Council is better than the integrative unity rationale, despite persistent objections to it.

Death by neurological criteria: expert definitions and lay misgivings

For decades, there has been persistent controversy concerning brain death, or the determination of death by neurological criteria, among physicians, philosophers, and the lay public. This article examines the various ways that brain death is conceptualized and justified, as well as the persistent questions and controversies related to brain death, particularly within pluralistic, multicultural societies. A culturally sensitive and practical way forward is proposed.

Controversies in defining and determining death in critical care

Circulatory-respiratory or brain tests are widely accepted for definition and determination of death, but have several controversial issues. Both determinations have been stimulated by organ donation, but must be valid independently of this process. Current controversies in brain death include whether the definition is conceptually coherent, whether the whole-brain or brainstem criterion is correct, whether one neurological examination or two should be required, and when to conduct the examination following therapeutic hypothermia. Controversies about the circulatory determination of death include the minimum duration of asystole that is sufficient for death to be declared, and whether the distinction between permanent and irreversible cessation of circulatory functioning is important. In addition, the goal of organ donation raises issues such as the optimal way to time and conduct the request conversation with family members of the patient, and whether the Dead Donor Rule should be abandoned.

Irreversibility: cardiac death versus brain death

The acceptance of brain death (BD) as death of the human being has been progressively accepted beginning in the early 1960s. The issue of irreversibility is directly related to the diagnosis of human death, and it is closely associated with the concept of potentiality, i.e., that some patients still have the potentiality of living. In recent years several authors have proposed to use a cardiocirculatory criterion for death determination in transplant donors. This has aroused ethical and medical controversies regarding concerns to accept that a non-heart-beating donor is really dead. We conclude that the cardiocirculatory criterion of death only assures irreversibility when asystole is prolonged enough to assure that ischemia and anoxia have destroyed the brain. On the contrary, BD fulfills both requirements for death determination: cessation of functions and irreversibility

Persistent vegetative and minimally conscious states

The diagnosis and management of patients with persistent vegetative (PVS) and minimally conscious (MCS) states entail powerful medical, ethical and legal debates. The recent description of the MCS highlights the crucial role of unexpected and well-documented recoveries of cognitive functions. Functional neuroimaging has provided new insights for assessing neuropathology and cerebral activity in these patients, providing information on the presence, degree, and location of any residual brain function in patients with PVS or MCS. We present a review on this topic, emphasizing the clinical and neuroimaging assessment of these states, with some of our recent results in this area. We conclude that the development of rehabilitation techniques for patients with PVS and others suffering long-lasting effects of brain injury is a crucial challenge for actual and future generations of neuroscientists.

Towards an effective definition of death and disorders of consciousness

There exists much controversy in providing an effective definition of human death, largely due to the lack of a rigorous separation and ordered formulation of three distinct elements: a universally accepted definition of death, the medical criterion (anatomical substrata) for determining that death has occurred, and the tests to prove that the criterion has been satisfied. The papers herein review medical standards, philosophical arguments, neurophysiological knowledge, behavioural and cognitive theory and the legal ramifications of the brain-oriented standards of death (whole brain, brainstem and higher brain). The papers examine the notion of connectivities and networks of conscious experience in order to formulate an effective definition of death, based on the basic physiopathological mechanisms of consciousness. We cannot simply differentiate and locate arousal as a function of the ascending reticular activating system, and awareness as a function of the cerebral cortex. Substantial interconnections among the brainstem, subcortical structures, and the neocortex are essential integrating components of human consciousness. This paper attempts to reconcile the brain-oriented standards that are currently inconsistent. The thread of the arguments is the basis for a standard of human death that includes consciousness as the most important function of the body, because it provides the capacity for integrating the functions of the body. The notion of consciousness as the ultimate integrative function is more consistent with the biologically-based systems than the more philosophically-based notions of personhood. Both sides of the argument are presented herein.

Brief review: the role of ancillary tests in the neurological determination of death

PURPOSE

The acceptance of brain death by society has allowed for the discontinuation of "life support" and the transplantation of organs. In Canada we accept the clinical criteria for brain death (essentially brain stem death) when they can be legitimately applied. Ancillary tests are needed when these clinical criteria cannot be applied or when there are confounders. Ancillary tests include tests of intracranial blood circulation, electrophysiological tests, metabolic studies and tests for residual vagus nerve function. The ideal confirmatory test is one which, when positive, would be incompatible with recoverable brain function (i.e., has no false positives), is not influenced by drugs or metabolic disturbances and which can be readily applied. A critical review of the various ancillary tests used to support the neurological determination of death (brain death) was undertaken.

METHODS

A literature review based on a MEDLINE search of relevant articles published between January 1966 to January 2005 was undertaken.

RESULTS

Tests of whole brain perfusion/intracranial blood circulation are the only ones that meet stated criteria.

CONCLUSIONS

At present only cerebral angiography and nuclear medicine tests of perfusion are accepted by Canadian standards, but computed tomography and magnetic resonance angiography should prove to be suitable. Transcranial Doppler studies may be suitable for specific cases once appropriate guidelines are established.