Stem-cell research aimed at regenerating nerve cells in the human brain is moving forward. Researchers have already isolated a particular gene that directs certain stem cells to turn into cerebral cortex cells. These are the cells comprising the outer layer of the cerebrum, the upper part of the brain largely responsible for cognition. Researchers have also been able to “reawaken” the generative powers of stem cells that lie dormant in the brain stem, the lower part of the brain that controls autonomic functions such as breathing and heart rate. They have even begun to transplant stem cells into the brains of stroke victims.
These and other breakthroughs of the past year alone point to the imminent possibility of being able to regenerate the cerebral cortex or brain stem of a human brain that has become nonfunctional due to trauma, diseases such as Parkinson’s and Alzheimer’s, or even old age. Predictably, this progress will raise serious ethical challenges.
So far, most of the ethical discussion surrounding cloning and stem-cell research has focused on the morality of cloning entire humans or on whether the process of organ cloning leads to the destruction of a human being. However, the use of stem cells to generate or regenerate the human brain raises other very serious ethical challenges about which there has been little or no discussion. To name one, what implications might such technological advances have on our current definition of clinical death? A related issue concerns the ethics of regenerating the brain of a patient who, by current medical and legal standards, would be declared clinically dead. This article will raise potential problems and suggest possible ways of addressing them.
The Current Definition of Clinical Death
In 1968, an ad hoc committee of the Harvard Medical School published a landmark article describing what it called “irreversible coma” and proposed that this state be identified with clinical death. The criteria the committee proposed was a permanently nonfunctioning brain, including both the upper and lower brain. This definition—which subsequently replaced the earlier definition found in Black’s Law Dictionary that defined death as the complete cessation of circulation and respiration—became the accepted statutory definition of clinical death.
The reasons the Harvard committee gave to justify the new definition were pragmatic and technology-driven. It maintained that because of new life-support technologies, patients whose hearts continued to beat but whose intellects were permanently destroyed due to irreversible brain damage were futilely taking up scarce hospital facilities. Second, obsolete criteria for defining death caused shortages of obtaining vital organs for transplantation. The new definition was intended to circumvent these practical problems by permitting patients to be pronounced dead while their hearts were still beating.
However, as advances in stem-cell research proceed to the point of being able to regenerate nerve cells, the Harvard definition of irreversible coma may itself be rendered obsolete, because this new technology would permit repair of damaged brain matter.
According to the Harvard definition, to be in an irreversible coma, a patient must lack spontaneous respiration. That is, a patient who is breathing on a respirator must not be able to breathe on his or her own when the respirator is turned off. However, if the nerve cells in the damaged region that control breathing (the brain stem) could be regenerated, spontaneous breathing could be restored. Thus a patient without any upper or lower brain functions (that is, having a totally nonfunctioning brain) could still not be “clinically dead” as defined by the Harvard committee. With the advent of new stem-cell technology, the loss of brain function would no longer be permanent (as required by the Harvard definition) insofar as the damage to the brain stem that prevents spontaneous respiration could be repaired.
Of course, the patient’s surrogate might choose not to repair the brain-stem damage and hence not restore spontaneous respiration. Instead, the surrogate might choose to remove the patient from the respirator and “let nature take its course.” But this would be passive euthanasia (allowing the patient to die), which would already presuppose that the patient was not clinically dead in the first place. Therefore, in any event, the advent of stem-cell technology for regenerating brain cells would make the Harvard definition of clinical death obsolete.
Moreover, in an age of stem-cell technology for repair or replacement of diverse body parts (for example, kidneys and hearts), the Harvard committee’s rationale for requiring loss of spontaneous respiration as a standard of clinical death would also be obsolete. According to this rationale, organ donors unable to breathe on their own could be pronounced dead while they continued to breathe artificially on a respirator. In this way, the donor’s organs could be kept vital up to the moment they were harvested. However, with the ability to regenerate new organs using stem-cell technology, a definition of death justified by its utility for organ transplantation would no longer be necessary, since traditional organ transplantation itself would be rendered obsolete. The cloning of organs from stem cells derived from the patient’s own body avoids the life-threatening consequence of organ rejection, which arises when an organ is transplanted from one patient’s body into another’s.
Accordingly, the advent of stem-cell technology would leave us with a need for further redefinition of clinical death. What might this new definition include?
The Cerebrum as the Locus of Personal Identity
As discussed, such a definition could no longer include loss of spontaneous respiration as a condition of clinical death. The locus of functionality might then shift to the upper brain: the cerebrum. However, in this case, the use of stem cells to regenerate damaged (cerebral cortical) brain cells would add a different wrinkle to that of applying such technology to the brain stem: the cerebral cortex appears to be more closely linked to personal identity. For one, it seems to be where memories are stored. Hence the complete obliteration of the cerebrum as is the case in brain death is likely to mean the obliteration of all past memories.
As David Hume expressed, “Had we no memory we never shou’d have any notion of causation, nor consequently of that chain of causes and effects, which constitute our self or person.” That is, the sequence of all of our life experiences that make us who we are would be lost.
Consequently, insofar as the cerebrum contains the storage areas of a person’s memories and insofar as this area is destroyed, it would make sense to speak about the loss of the person as such. To the extent that this loss is complete and permanent, we could then say that the person is forever gone and therefore has “died.”
Of course, this is not how we presently speak about death. We would now speak of patients without cognitive function but who still have lower brain functions as being in a “persistent vegetative state” as distinct from being clinically dead. However, in a culture in which brain-stem functions such as respiration could be readily repaired by means of regenerating the damaged nerve cells in the brain stem, this distinction would appear to be one without a practical difference. With the availability of such technology, the practical difference between a living, breathing person and simply a breathing body would appear to lie in the status of the upper brain, the presumed locus of cognition and memory.
Just for the Memories
The precise mechanisms by which memories are stored in the brain are still not known. But if we could indulge our imaginations for a moment and suppose that these mechanisms were someday known, then it might be possible to make a sort of “backup copy” of this stored information in case the regions of the brain that store such information have been destroyed. We might then be able to regenerate the nerve cells in the damaged regions using stem-cell technology and copy the backed-up information to the restored brain, thereby reviving the person. With the advent of such memory restoration technology, we might then redefine death in terms of destruction of the memory-storage regions of the brain in the absence of a backup copy.
More realistically (at least at this juncture in time), we may soon be able to regenerate the cerebral cortex without salvaging the memories that were lost when the original cellular damage occurred. Regeneration of some regions of the cerebrum, in particular the hippocampus, might repair the capacity to create and store new memories (since the hippocampus appears to play a pivotal role in the processing of information for storage). However, this repair would not itself reinstall the former memories, which would have been “wiped out” with the destruction of the (entire) cortex.
This would leave us in a curious situation. The body of a former person might remain biologically intact while attached to a ventilator. Even with a totally nonfunctional brain, it might be possible to restore spontaneous respiration and regenerate a new cerebrum. Presumably, this new brain would be devoid of all previous memory stores, including skill sets that have been acquired over time and through practice. However, if a somatic stem cell such as one from the skin of the body that would house the new brain were utilized in regenerating the cerebrum, it would be a genetically identical brain to that which previously occupied the cranial cavity of this body.
In such a case, would we have revived the same person or a different person? This individual would have the same body, a genetically identical brain, and therefore similar capacities for thinking and reasoning (to the extent that these capacities are genetically determined). So, it would appear that we would have some cogent reasons in favor of calling this the same person. On the other hand, the newly revived individual would lack “that chain of causes and effects, which constitute our self or person.”
While the emergent culture would need to decide this question, my sense is that the revived individual might best be perceived and treated as a different person, not least of all because we should not expect this individual to be the same—to act, think, feel, and relate in precisely the same ways as the previous self. For that matter, in such a case, it might be best not to revive the individual in the first place and instead to face the somber truth that the unique person that once was the former self is now permanently and irrevocably clinically dead.