Some Issues in Contemporary Neurological Science and Technology
Adapted from a presentation at a "Works in Progress" forum sponsored by the Center for Biomedical Ethics at Stanford University on December 11, 2001.
I. The mind-brain puzzle
Modern advances in neurological science and technology pose profound challenges for our traditional concepts of the human person: they generate metaphysical and moral questions about beings at the edges of human life, from embryos that are not yet conscious, to persons who have lost their capacity for rational thought or have become permanently unconscious.
I’ll begin by framing these issues in the context of an ancient puzzle that has been the subject of much philosophical and religious debate: What is the relationship between the soul and the body (or the mind and the brain)? We take for granted the intimate connection between our minds and bodies. It’s difficult to imagine our selves as disconnected from the particular bodies we have. But we also have a strong intuition that consciousness is a truly extraordinary thing in nature.
Many people have thought that the only way to account for the qualitative distinction between brain and mind is to regard them as fundamentally different substances, one material, the other immaterial. The 17th-century philosopher Rene Descartes was one of the most famous proponents of that view, but religious traditions have affirmed similar beliefs for millennia. The attraction of such a concept is obvious: if our soul/mind is not a material thing, then it’s conceivably immortal. The soul might survive the death of the body in an afterlife, as the Jewish, Christian and Islamic religions teach. Or the soul might be reincarnated through a potentially unlimited succession of living bodies, as the Hindu or Buddhist traditions hold.
But there turn out to be serious conceptual problems with the belief that the mind and body are essentially different substances. If the soul is immaterial, then it can have no location in space, and thus cannot be contained by any physical brain or body. More importantly, an immaterial mind could never interact with material things or events like the electrical impulses and biochemical activities occurring constantly in and between our neural cells. The belief that the soul is immaterial also flies directly in the face of our daily experiences of being conscious of the physical world through our bodily senses of sight, hearing and touch. An immaterial mind could not be our mind; it would be utterly disconnected from our embodied experience and self-identity.
(Note also that immaterial ghosts/spirits could never be seen, heard or felt. On the other hand, if they’re asserted instead to be material beings, then their presence ought to be measurable through controlled scientific tests—none of which has ever proven their existence. See Schick & Vaughn 1999b.)
Modern neuroscience is systematically revealing the correlations between mental states and brain states, even if it hasn’t yet shown their causal relations nor proven that we’ll ever be able to express mental events entirely in electrical and biochemical terms. The most promising philosophical approach to the mind-brain puzzle—and one that is fully compatible with modern neuroscience—is known as "property dualism." This theory envisions the mind as an emergent property of individually unconscious neural cells when they interact in complex ways, analogous to wetness as an emergent property of water molecules, or life as an emergent property of amino acid molecules which are individually lifeless (Searle 1992; Schick & Vaughn 1999a). I cannot do justice to that theory in this short article. Suffice it to say that some appreciation of brain functioning is essential to understanding what it takes to have a mind.
II. Who or what is a person?
To be classified as a "person" normally entails having strong moral rights and legal protections, and higher moral status than living things that cannot credibly be classified as persons. But as Karen Gervais (1986) effectively argued, the more basic question here is a metaphysical or ontological one about the necessary and sufficient conditions for knowing when a particular kind of being exists or does not exist.
A. Five typical traits
According to philosopher Mary Anne Warren (1973), "the traits which are most central to the concept of personhood . . . are, very roughly, the following: 1. consciousness . . . and in particular the capacity to feel pain; 2. reasoning (the developed capacity to solve new and relatively complex problems); 3. self-motivated activity (activity which is relatively independent of either genetic or direct external control); 4. the capacity to communicate, by whatever means, messages of an indefinite variety of types . . . ; 5. the presence of self-concepts, and self-awareness. . . ."
Warren thinks that these traits comprise what we mean by a person in the full-blown sense, but that a being need not have all of these attributes in order properly to be considered a person in some sense. I think that most of us would agree with that. We might lose the ability to communicate and yet still remain the same essential person. And if self-motivated activity were truly a necessary condition for personhood, we’d all be in trouble some of the time!
But Warren seems to believe that reasoning is both a necessary and sufficient condition for personhood. This raises the intriguing possibility that some non-human animals like chimps and dolphins might qualify as persons, but also the disturbing implication that some human beings would not qualify, such as the severely retarded or demented. In other words, if we set the bar as high as Warren has, we logically exclude many vulnerable human populations from the category of persons, and thus from the rights we ascribe to persons, which is very troubling. (See Dombrowski 1997. For a fascinating study of non-human mental capacities, consult DeGrazia 1996.)
We thus need to consider whether another human capacity besides rationality could qualify as a necessary or sufficient condition for personhood. (I’ll ignore non-human animals in what follows.) One useful way to get at this is to reflect on our concepts of death:
B. Determining the death of persons
How can we know that a person has died, or when are we justified in declaring a person to be dead? Consider these contending criteria:
1. Decomposition When every last cell with a person's DNA has died (ignoring cells in donated blood and other organs): This is clearly a sufficient condition for the death of a person. It would seem utterly ridiculous as a necessary condition. But consider the Vatican’s claim that a person is fully present from conception, when there is only an undifferentiated embryo with a full complement of human DNA. Under that assumption, it’s hard to see how anything short of complete cellular decomposition would be sufficient to declare a person to be dead, since the cessation of heart, lung or brain function could not logically be sufficient conditions (Dombrowski & Deltete 2000). Moreover, in separating the mind from the organic development of the brain, the person-from-conception view seems to reflect a belief in an immaterial mind, which suffers from the fatal metaphysical flaws I mentioned earlier. These points effectively refute the claim that persons exist from conception.
2. Cessation of cardiopulmonary functions This used to be considered a sufficient condition throughout the world, and in a sense it remains so legally in the U.S. in cases when brain death is not possible to assess. It remains a necessary condition in some religions and cultures where the soul is identified with breath or the blood. Of course, the fact that we can resuscitate people with CPR after their breathing and heartbeat have stopped--and often revive them to a conscious state with their full personalities intact--proves that this criterion is not really a sufficient condition for the death of a person, and need not be considered a necessary condition. People who still believe that it is sufficient cannot also expect to be resuscitated or maintained on ventilators without contradicting themselves.
3. Whole-brain death i.e., the loss of function of the entire brain: The first clinical case of a brain-dead individual whose heart and lungs were maintained on a respirator was reported by French doctors in 1959. In 1968, an ad hoc committee at Harvard Medical School chaired by Henry Beecher recommended that doctors declare death based on the permanent loss of all brain functions (Bernat 1994; Pernick 1999). Whole-brain death is now a sufficient condition for declaring a person to be legally dead in every U.S. state. This standard conveniently incorporates two common-sense aspects of the death of a person, "the irreversible loss of the capacity for consciousness and the irreversible cessation of integrated functioning of the organism as a whole" (McMahan 1998).
4. Higher-brain/neocortical death Many philosophers have questioned, though, whether whole-brain death is a necessary condition for the death of a person (Veatch 1975, 1993; Gervais 1986; Cranford & Smith 1987; McMahan 1995). If what really matters is the permanent loss of consciousness, then in theory we could declare persons dead even if they were not whole-brain dead. This view is consistent with the idea—which I find compelling—that a person's life is coextensive with his or her capacity for experience and thought. By this definition, human beings in permanent comas and persistent vegetative states would be dead persons.
Depending on etiology, clinical diagnosis of permanent unconsciousness prior to whole-brain death can be fairly certain after three months to one year, and quite certain with positron emission tomography tests (Levy et al. 1987; Cranford & Smith 1987). To avoid the risk of abuse, e.g., when death by higher-brain standard might be declared prematurely in order to eliminate the financial burden on others of continued treatment, lawmakers could easily stipulate very conservative criteria, such as PET scans showing that the entire cerebral cortex no longer functions.
What would it mean to adopt the higher-brain standard as a sufficient condition for declaring persons to be dead?
III. Some ethical considerations under the higher-brain approach
A. Coma, PVS and anencephaly
If human beings in permanent comas or persistent vegetative states are no longer persons, then life-sustaining medical treatment is qualitatively futile for them. No one is "there" anymore to benefit from such treatment; while biological life may continue, the "subject" of that life is gone. Of course, if life-sustaining treatment were maintained in order to preserve organs for harvesting, then it would not be futile in every sense.
Two advantages of the higher-brain definition of death are: assaults producing this appalling condition could be charged as homicides; and money now spent on utterly futile treatments could be used instead to benefit living persons (Cranford & Smith 1987). But there are also some disadvantages: higher-brain death can be more difficult to diagnose than whole-brain death; and PVS individuals would temporarily continue to breathe spontaneously and have "wake-sleep" cycles after withdrawal of feeding tubes, so declaring them dead might be disturbing to caregivers--though perhaps not much more disturbing than PVS itself. At the very least, it would be important to wait until the heart stopped before burying or cremating the body! (The claim by Bernat 1994 that under the higher-brain standard we would be logically required to treat a breathing PVS human being as any other corpse is a red herring and simply not true.)
Anencephaly is a catastrophic malformation of the brain that originates in developmental errors in the early embryo, preventing the formation of a functioning cerebral cortex (Medical Task Force on Anencephaly 1990). Although anencephalic fetuses and infants usually have working brainstems (as in PVS), they permanently lack a capacity for consciousness and thus can never become persons under the higher-brain definition (Cranford & Smith 1987; Walters et al. 1997). Although they are legally alive, the case for changing the law is compelling to me, whether or not they would then be considered appropriate sources of transplant organs.
But if whole-brain death remains the legal standard, should the "dead-donor" rule be modified to permit organ harvesting prior to whole-brain death? Imagine that someone were to state in their living will that should they succumb to PVS, their body may be maintained on life-support and used not only as a source of organs but for testing drugs, training medical and nursing students on intubation and other procedures, or even dissection. This initially seemed an attractive option to me, but now I’m more troubled by it, seeing as it would set a precedent of using individuals who were not legally dead simply for the benefit of others. So I would prefer if higher-brain death became legally recognized as sufficient for declaring the death of a person, though I doubt that this will be politically possible for many years.
Do patients and surrogates have the moral right to insist on life-sustaining treatment even after permanent loss of consciousness? I tend to think not, even though stopping treatment would offend many people on religious or moral grounds. (Note that we already permit physicians to declare death by whole-brain criteria even when family members object.) But in order to limit distress to patients and surrogates who won’t accept the higher-brain criteria of personhood, it may be more compassionate not to mandate withdrawal of feeding tubes as a strict policy, but rather to educate people about the nature of PVS and the futility of treatment.
B. Moral status of human embryos and fetuses
Many empirical studies indicate that sentience is not possible before 20 weeks gestation, and may not emerge until much later. Prior to 20 weeks, although billions of neurons have already migrated to the cerebral cortex, there are almost no synaptic connections between them or with the thalamus, which mediates sensory perception. Partly because of the ambiguity of fetal EEG patterns, it’s difficult to say precisely when consciousness first occurs. But somewhere between 20 and 32 weeks gestation, the cortical neurons become capable of firing in ways that make consciousness possible. The brainstem and nervous system may function before that time, and there may be reflex reactions to stimuli, but there is no one "there" yet to experience sensory inputs—the lights are on, but nobody’s home. (Anand & Hickey 1987; Flower 1989; Morowitz & Trefil 1992) Since early embryos and fetuses cannot experience harm, they lack interests of their own which are necessary to have moral rights. Under the higher-brain standard, they do not become persons until the onset of consciousness (Steinbock 1992; Robertson 1994).
It’s worth pointing out that the criterion of neocortical functioning is distinct from viability and birth, both of which have legal significance in the U.S. Since Roe v. Wade, federal law prohibits states from giving fetuses the status of persons prior to birth, though in regulating abortion it grants states a "compelling interest" in fetal life from viability. But neither viability nor birth is directly correlated with the capacity for consciousness (Gertler 1986), and no federal or state law confers any significance on the latter.
Even if laws were changed, though, to accord late-term fetuses the rights of persons because of their capacity for consciousness, this would not entail a total ban on late-term abortions, since other laws permit the killing of persons in self-defense, and almost never require people to risk their health substantially in order to save others' lives. For example, U.S. courts have been unwilling to force people to donate bone marrow or kidneys, even if potential recipients are a perfect match and will die for lack of them (Rhoden 1994). Ninety-eight percent of abortions in this country are performed within the first 15 weeks of pregnancy anyway, and most of the rest occur when the mother’s life or health is at risk or in cases of severe fetal abnormality. However, if conscious fetuses were legally recognized as persons, a woman seeking a late-term abortion might be required to show that continuing her pregnancy posed a threat to her life or health. Federal law currently permits states to enact a similar restriction regarding viable fetuses, but doesn’t require them to do so.
The NIH Human Embryo Research Panel (1994) recommended that experiments on embryos left over from in vitro fertilization should be restricted to a period of 14 days after conception, correlated with the appearance of the "primitive streak." But the actual metaphysical and moral significance of that development is trivial. Higher-brain criteria of personhood would seem to permit such experiments well after 14 days, as well as the use of embryos and early fetuses as sources of neural cells for transplantation to treat brain diseases (Dunnett & Bjorklund 2000; Chadwick & Goode 2000; Barinaga 2000). This also has significant implications for the contemporary debate regarding "therapeutic" cloning to derive stem cells. Even the intentional creation of embryos for experimental purposes only, as long as those embryos were not sustained to the point when consciousness became possible, would not by itself constitute a violation of the rights of persons (Steinbock, 1992 Robertson 1994). Note that I have focused exclusively here on the moral status of the human embryo or fetus in itself, ignoring the value that its parents might ascribe to it. It would be clearly wrong to use an embryo or fetus even for weighty purposes without the informed consent of the parents.
IV. Brain damage, advance directives, and current best interests
At some point in progressive dementia, or as a result of a devastating stroke or head injury, the loss of memory and rational capacity can greatly alter and diminish the self, and render one incompetent to make decisions about medical treatment. Of course, one ought to remain a "moral patient" with basic rights well after one is no longer capable of being a moral agent. Ethicists rightly worry that helpless individuals could wrongly be allowed to die without consideration of what is in their own interests, whether they benefit from continued treatment, and whether life is or could be still worth living from their point of view. But other ethicists are troubled by the idea of overriding a previously competent person's preferences—e.g., not to have CPR or tube-feeding—in order to promote their best interests after they become incompetent. Let's examine closely two contending perspectives on the relative importance of consequentialist and non-consequentialist principles.
A. Rebecca Dresser and John Robertson (1989)
Incompetent patients by definition have impaired self-determination or autonomy. Yet as Dresser and Robertson pointed out, courts have granted such patients the right to refuse treatment as if they were competent. "What patients would have wanted" if they were still competent is given great weight, hence the importance of advance directives and substituted judgment.
But D & R claimed that such patients' current interests may be very different from their past preferences as competent persons. Previously, the things that mattered to them were work, family, friends, independence, and privacy; but now, "what was once of extreme importance to them no longer matters. . . . An existence that seems demeaning and unacceptable to the competent person may still be of value to the incompetent patient, whose abilities, desires, and interests have so greatly narrowed." This means that preferences stated by patients when competent may conflict with and be detrimental to their interests after they become incompetent. Also, advance directives usually don't specify conditions of incompetence in enough detail. This may indicate lack of awareness by competent persons as to how their interests can change, raising further doubt about the justification of honoring advance directives. Hence, according to D & R, using advance directives without regard to current interests is morally problematic.
Substituted judgment also risks allowing the biases of caregivers to negate patients' current interests: as competent persons, caregivers may be distressed by conditions they find degrading. In the case of Spring, dialysis for a demented elderly man was stopped upon his family's request. But the reliance on substituted judgment "ignored the possibility that in his incompetent state he obtained sufficient countervailing pleasure and satisfaction to make the benefits of continued life outweigh the discomforts of the dialysis necessary to preserve that life." Also, in the case of Hier the patient's removal of her feeding tube was seen as a "plea for privacy and personal dignity," in spite of the fact that those concerns are ones that only rational individuals can have. The court also neglected the suffering she might experience from withdrawal of her feeding tube, as well as whether she obtained some enjoyment from her life. (Note the potential need for physical or chemical restraints in such cases, though, in order to continue life-sustaining treatments.)
D & R advocated a modified "best interests" standard, focusing on patients' subjective states, quality of life, or current and future welfare, consistent with our obligations of beneficence and nonmaleficence. "The question is not how a competent person would feel in such states, but whether these experiences are of value to a person in the incompetent person's situation. The important question is whether patients who cannot experience the richness of normal life still have experiences that make continued existence from their own perspective better than no life at all." This approach would also permit non-treatment to occur, though, "when the patient cannot reasonably be said to have any continued interest in living because her level of awareness is so minimal that the patient is unable to appreciate being alive." Thus withholding or withdrawing life-sustaining treatments could be justified even in cases where the treatment itself would not cause suffering.
B. Nancy Rhoden (1990)
Rhoden objected to the exclusive focus on present best interests advocated by D & R, primarily because it undermines respect for the preferences of previously competent persons as reflected in advance directives and the values they expressed to loved ones. "Under a present-oriented view, we would respect choice as long as the person was competent, but then, once his powers dimmed, we would rethink it if treatment was still potentially efficacious. . . . [T]hen the competent patient's 'right' to refuse treatment will be upheld only for the [period in which] she remains competent. After that, the treatment decision will be made on the basis of the objectively assessed present interests of the incompetent. Taken to an extreme, this could mean that a Jehovah's Witness could refuse a blood transfusion until he 'bled out' and became incompetent, after which he could be transfused." Or surgery might be performed on a Christian Scientist to preserve his incompetent self, despite his directive (consistent with his religion) when previously competent to refuse all surgery.
Against D & R's criticism of advance directives and substituted judgment, Rhoden claimed that we’re obliged to uphold the wishes of previously competent persons even when they conflict with the interests of their presently incompetent selves. "The competent person's primacy derives from his status as moral agent. Moral agency is inherently future-directed, and the future may, unfortunately, encompass one's incompetency. Prior directives are the tools for projecting one's moral and spiritual values into the future." For an incompetent person, former values are still important because they reflect autonomous choices. "Something is wrong . . . when we treat formerly competent patients as if they were never competent. Someone who makes a prior directive sees herself as the unified subject of a human life. She sees her concern for her body, her goals, or her family as transcending her incapacity."
A person who creates a living will or otherwise communicates her preferences, goals and values to her family or friends "imposes upon others a prima facie duty to honor" those choices. "Viewing the patient only in the present divides her from her history, her values, and her relationships--from all those things that made her a moral agent. . . . If a person has stated, 'Treat me, when incompetent, as if my competent values still hold,' respect for persons demands that we do so." Our duties can be "backward-looking," fulfilled or violated in relation to persons as they were. Thus unlike D & R, Rhoden saw an important similarity between living wills and testamentary wills or bequests. Breaching either one can be seen as breaking promises toward previously competent persons.
However, in the absence of living wills there could still be a need to guard against family biases creeping into substituted judgment, especially when they conflict with apparent current interests (a point noted by D & R). And even Rhoden seemed to think that there are some preferences of competent patients that should not be honored, such as a hypothetical case she mentions where an intellectual demands not to be treated if he becomes even slightly impaired mentally. But then, Rhoden would add that we should never promise to honor such a demand in the first place.
Unfortunately some advance directives focus exclusively on terminal illness and permanent unconsciousness, ignoring matters of quality of life for conscious but incompetent patients who may not be terminally ill. Competent patients should be encouraged to write advance directives that reflect a nuanced understanding of the choices that their caregivers might face if they become incompetent (King 1996). Patients might be asked, "If you reach a point when you’re no longer able to care for yourself or tell us what you want, yet you still seem to enjoy living, should we keep you alive even if the treatments cause you some discomfort? Would you want to be on a respirator or feeding tube if it allowed you to remain in conscious contact with your family and friends?"
An expression of values and preferences under such conditions should reduce the likelihood of a conflict between previously competent persons' stated wishes and assessments of their best interests by proxies and caregivers. D & R have helpfully reminded us that we should avoid assuming that the loss of our capacity to reason or communicate would necessarily result in a miserable existence: as a demented person, we may no longer care about many abilities that we now treasure as essential to our self-identity and self-respect, and so would not perceive their loss as tragic or undignified. But as Rhoden argued, if we promise to uphold the values and preferences of rational and informed persons, then we must keep those promises when they become incompetent, even if we think it would be better for them if we chose otherwise.
Human beings can only sensibly said to be persons to the extent that they are capable of conscious experience. That capacity first emerges in the human fetus between 20 and 32 weeks gestation, and can be irreversibly lost if the cerebral cortex permanently stops working, even if the brainstem continues to function with respirator support. Thus, early abortions, experiments on human embryos and early fetuses, and withdrawal of feeding tubes from PVS individuals do not in themselves represent violations of the rights of persons.
Although rationality is usually seen to be the sine qua non of personhood, granting the highest degree of moral status only to rational beings would entail morally unacceptable implications for infants, the demented, and severely retarded people. Human beings with the capacity for consciousness ought to be regarded as persons—metaphysically and morally—even if they can’t reason or communicate.
But it is also important to uphold the values and preferences of formerly rational people after they become incompetent—even if their previously stated wishes conflict with what caregivers later to be in their best interests—as long as those wishes were made with an adequate appreciation of the quality of life that incompetent people are capable of enjoying. Rational agents should not simply assume that a demented life—whether their own or someone else’s—is no longer worth sustaining.
References and other recommended readings
Anand, K. and P. Hickey, 1987. "Pain and Its Effects in the Human Neonate and Fetus," New England Journal of Medicine, November 19.
Barinaga, Marcia, 2000. "Fetal Neuron Grafts Pave the Way for Stem Cell Therapies," Science, February 25.
Bernat, James, 1994. Ethical Issues in Neurology.
Chadwick, Derek and Jamie Goode, eds., 2000. Neural Transplantation in Neurodegenerative Disease: Current Status and New Directions.
Cranford, Ronald and David Smith, 1987. "Consciousness: The Most Critical Moral (Constitutional) Standard for Human Personhood," American Journal of Law & Medicine 13/2-3.
DeGrazia, David, 1996. Taking Animals Seriously: Mental Life and Moral Status.
Dombrowski, Daniel, 1997. Babies and Beasts: The Argument from Marginal Cases.
________ and Robert Deltete, 2000. A Brief, Liberal, Catholic Defense of Abortion.
Dresser, Rebecca and John Robertson, 1989. "Quality of Life and Non-Treatment Decisions for Incompetent Patients: A Critique of the Orthodox Approach," Law, Medicine & Health Care, Fall.
Dunnett, Stephen and Anders Bjorklund, eds., 2000. Functional Neural Transplantation II: Novel Cell Therapies for CNS Disorders (Progress in Brain Research, vol. 127).
Flower, Michael, 1989. "Neuromaturation and the Moral Status of Human Fetal Life," in Edd Doerr and James Prescott, eds., Abortion Rights and Fetal "Personhood."
Gertler, Gary, 1986. "Brain Birth: A Proposal for Defining When a Fetus Is Entitled to Human Life Status," Southern California Law Review 59.
Gervais, Karen, 1986. Redefining Death.
King, Nancy, 1996. Making Sense of Advance Directives, revised edition.
Levy, David et al., 1987. "Differences in Cerebral Blood Flow and Glucose Utilization in Vegetative Versus Locked-in Patients," Annals of Neurology 22/6, December.
McMahan, Jeff, 1995. "The Metaphysics of Brain Death," Bioethics, April.
________, 1998. "Brain Death, Cortical Death, and Persistent Vegetative State," in Helga Kuhse and Peter Singer, eds., A Companion to Bioethics.
Medical Task Force on Anencephaly, 1990. "The Infant with Anencephaly," New England Journal of Medicine, March 8.
Morowitz, Harold and James Trefil, 1992. The Facts of Life: Science and the Abortion Controversy.
Multi-Society Task Force on PVS, 1994. "Medical Aspects of the Persistent Vegetative State," New England Journal of Medicine, May 26 and June 2.
National Institutes of Health, Human Embryo Research Panel, 1994. Report, volume 1.
Pernick, Martin, 1999. "Brain Death in a Cultural Context: The Reconstruction of Death, 1967-1981," in Stuart Youngner et al., eds., The Definition of Death: Contemporary Controversies.
Rhoden, Nancy, 1990. "The Limits of Legal Objectivity," North Carolina Law Review, June.
Robertson, John, 1994. Children of Choice: Freedom and the New Reproductive Technologies.
Schick, Jr., Theodore and Lewis Vaughn, 1999a. Doing Philosophy.
________, 1999b. How to Think about Weird Things, second edition.
Searle, John, 1992. The Rediscovery of the Mind.
Steinbock, Bonnie, 1992. Life before Birth: The Moral and Legal Status of Embryos and Fetuses.
Veatch, Robert, 1975. "The Whole-Brain-Oriented Concept of Death: An Outmoded Philosophical Formulation," Journal of Thanatology 3.
________, 1993. "The Impending Collapse of the Whole-Brain Definition of Death," Hastings Center Report, July-August.
Walters, James et al., 1997. "Anencephaly: Where Do We Now Stand?" Seminars in Neurology 17/3.
Warren, Mary Anne, 1973. "On the Moral and Legal Status of Abortion," The Monist 57/1.
________, 1997. Moral Status: Obligations to Persons and Other Living Things.
Wikler, Daniel, 1988. "Not Dead, Not Dying? Ethical Categories and Persistent Vegetative State," Hastings Center Report, February-March.
This article is copyright by David L. Perry. None of his views should necessarily be construed to represent those of the Markkula Center for Applied Ethics or Santa Clara University.
David Perry was the Director of Ethics Programs, Markkula Center for Applied Ethics, and Lecturer in Religious Studies.