Molecular machines can build cells from scratch, as dividing cells demonstrate. They can also build organs and organ systems from scratch, as developing embryos demonstrate. Physicians will be able to use cell repair technology to direct the growth of new organs from a patient's own cells. This gives modern physicians great leeway in biostasis procedures: even if they were to damage or discard most of a patient's organs, they would still do no irreversible harm. Future colleagues with better tools will be able to repair or replace the organs involved. Most people would be glad to have a new heart, fresh kidneys, or younger skin.
But the brain is another matter. A physician who allows the destruction of a patient's brain allows the destruction of the patient as a person, whatever may happen to the rest of the body. The brain holds the patterns of memory, of personality, of self. Stroke patients lose only parts of their brains, yet suffer harm ranging from partial blindness to paralysis to loss of language, lowered intelligence, altered personality, and worse. The effects depend on the location of the damage. This suggests that total destruction of the brain causes total blindness, paralysis, speechlessness, and mindlessness, whether the body continues to breathe or not.
As Voltaire wrote, "To rise again — to be the same person that you were—you must have your memory perfectly fresh and present; for it is memory that makes your identity. If your memory be lost, how will you be the same man?" Anesthesia interrupts consciousness without disrupting the structure of the brain, and biostasis procedures must do likewise, for a longer time. This raises the question of the nature of the physical structures that underlie memory and personality.
Neurobiology, and informed common sense, agree on the basic nature of memory. As we form memories and develop as individuals, our brains change. These changes affect the brain's function, changing its pattern of activity: When we remember, our brains do something; when we act, think, or feel, our brains do something. Brains work by means of molecular machinery. Lasting changes in brain function involve lasting changes in this molecular machinery — unlike a computer's memory, the brain is not designed to be wiped clean and refilled at a moment's notice. Personality and long-term memory are durable.
Throughout the body, durable changes in function involve durable changes in molecular machinery. When muscles become stronger or swifter, their proteins change in number and distribution. When a liver adapts to cope with alcohol, its protein content also changes. When the immune system learns to recognize a new kind of influenza virus, protein content changes again. Since protein-based machines do the actual work of moving muscles, breaking down toxins, and recognizing viruses, this relationship is to be expected.
In the brain, proteins shape nerve cells, stud their surfaces, link one cell to the next, control the ionic currents of each neural impulse, produce the signal molecules that nerve cells use to communicate across synapses, and much, much more. When printers print words, they put down patterns of ink; when nerve cells change their behavior, they change their patterns of protein. Printing also dents the paper, and nerve cells change more than just their proteins, yet the ink on the paper and the proteins in the brain are enough to make these patterns clear. The changes involved are far from subtle. Researchers report that long-term changes in nerve cell behavior involve "striking morphological changes" in synapses: they change visibly in size and structure.
"Memory and personality do not waft away on the last breath as a patient expires The patterns of mind are destroyed only when and if the attending physicians allow the patient's brain to undergo dissolution."
It seems that long-term memory is not some terribly delicate pattern, ready to evaporate from the brain at any excuse. Memory and personality are instead firmly embodied in the way that brain cells have grown together, in patterns formed through years of experience. Memory and personality are no more material than the characters in a novel; yet like them they are embodied in matter. Memory and personality do not waft away on the last breath as a patient expires. Indeed, many patients have recovered from so-called "clinical death," even without cell repair machines to help. The patterns of mind are destroyed only when and if the attending physicians allow the patient's brain to undergo dissolution. This again allows physicians considerable leeway in biostasis procedures: typically, they need not stop metabolism until after vital functions have ceased.
It seems that preserving the cell structures and protein patterns of the brain will also preserve the structure of the mind and self. Biologists already know how to preserve tissue this well. Resuscitation technology must await cell repair machines, but biostasis technology seems well in hand.
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