Long before neuroscientists took the first tentative steps toward brain-tissue transplants (let alone dared to think about whole-brain transplants), mischievous philosophers were plumbing the consequences of such 21st century surgery. "In a brain-transplant operation, is it better to be the donor or the recipient?" these wags asked. To put it another way, if you and Tom manage to swap brains, who is now the real you? The man with your brain attached to Tom's body or the man with Tom's brain joined to your body?

The real you, it can be argued, is the man with Tom's body; he's the one who knows the most intimate and embarrassing details of your life. The man with your former body may now have a bum knee, but he won't know why (that misguided dive you took playing touch football to impress your girlfriend in 1971). Summing up his own theoretical musings about the wisdom of a brain swap, Tufts University philosopher Daniel Dennett concluded that it was not an even exchange. "It was clear that my current body and I could part company, but not likely that I could be separated from my brain," he wrote. "The rule of thumb [is] that in a brain-transplant operation, one want[s] to be the donor, not the recipient."

Whole-brain transplants are still science fiction. "I never like to say that something's impossible," says Dr. Evan Snyder, a neuroscientist at Harvard Medical School and Children's Hospital in Boston. "I've been burned too many times by categorically ruling something out. And yet I can't imagine that 20 years from now human-brain transplants will be possible. The connections required are just too complex; they number in the millions. But the future of brain-cell transplants--that's another matter."

So far, medical science has had only mixed results with brain-cell transplants. Take the treatment of Parkinson's disease, for example, a condition that is gradually depriving more than 1 million Americans of their ability to move and speak. The disease is caused by the slow deterioration of brain cells that produce dopamine, a chemical essential for the transmission of messages from the brain to the rest of the body. A decade ago, Swedish researchers started implanting dopamine-producing cells from human fetuses into the brains of Parkinson's patients. The treatment improved the mobility of many of the patients but usually only partly and in some cases not at all. Even if the treatment becomes more successful (and the ethically charged issue of mining aborted fetuses is overcome), it can hardly become routine. For each patient, cells from as many as 15 fetuses must be harvested and transplanted almost immediately. MORE>>

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