Because technology can substitute for many brain functions (spontaneous respiration, cardiovascular support, and neuroendocrine regulation), a more refined definition that emphasizes functions that cannot be replaced through technology may be appropriate. In fact, we are replacing brain stem functions with ever-increasing success. (Youngner and Bartlett 1983)
Future medical technology may enable us to keep the brain stem alive or replace it entirely, thus preventing brain-stem death. (Ray 1991)
The British brain death policy requires only that the brain stem has been destroyed to declare death, and many commentators have noted that it is technically possible to substitute for brain stem function with intensive monitoring (Youngner and Bartlett 1983)). Prolonged survival of a patient with a mechanical brain stem, but otherwise intact cognition, would show the inadequacy of a brain stem definition, and perhaps also of the whole brain definition which implicitly asserts the pivotal role of the brain stem.
The remediation of damage to the cerebral hemispheres is currently beyond our abilities, but the discovery of the special malleability of fetal brain tissue, and the ability to stimulate neural cell growth and division with neurotrophic chemicals or gene therapy, raises the possibility that patients with extensive brain damage, sufficient to currently be considered dead, at least by higher-brain standards, may be able to returned to some degree of function (Tuszynski and Gage 1995; Valouskova and Galik 1995; Olson 1993). Of course, they will probably continue to be disabled in many ways, and have lost much of their memory. The question these technologies may raise is how much of one's motor skills, memory and cognition one may lose to be treated as dead, "socially dead" or "sick enough to not require further medical treatment or feeding," if those abilities can eventually be restored. McMahan asserts that the complete replacement of the cerebral tissues would constitute a new person:
Replacement of the (cerebral) tissues through the transplantation of new hemispheres might make consciousness possible, but this would not count as receiving the same mind, even if the new hemispheres were perfect duplicates of those destroyed. There would be a new and different mind. (McMahan 1995: 105)
The subjective experience of such a person would presumably be the same as an infant; the slow creation of meaning, acquisition of linguistic skills, and construction of a self-concept.
We might deal with such eventualities the way we deal with brain dead pregnant women, from whom we also have the possibility of bringing forth new life if we continue to maintain their socially dead bodies. Generally, in the United States, we would honor prior expressed wishes of such women to be maintained to term, and some would support the rights of husbands to make this decision without their wives' prior expressed wishes. On the other hand, we also honor the patient's or surrogate's request to perform an abortion on pregnant women in PVS on the grounds that the rights of the real or prior persons trump those of the potential persons. Since potential people don't have rights, the former person or their surrogates could request that the remediative techniques not be used to develop a new potential person.
Perhaps similarly we could add another layer of complexity to advance directives, asking if patients would want their brains to be used by a new tenant. The legal question is whether this successor would be the owner of the previous tenant's property, be married to their successor's spouse, be liable for the successor's crimes, and so on. The social life and death concept advanced above suggests they should not be held to be the same person.
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