The world’s first full head transplant could take place as soon as 2017 if the controversial plans by Italian neuroscientist Dr Sergio Canavero come to pass. Wheelchair-bound Valery Spiridonov, who has the muscle-wasting Werdnig Hoffman disease, has volunteered to have his head transplanted onto a healthy body in a day-long operation.

The proposed surgery is highly controversial and its feasibility has been questioned by experts. But Dr Canavero’s plans also raise complex philosophical and ethical issues. A natural question is whether a living person with Spridinov’s head and someone else’s body would be the same person as Spridinov. In interviews, Spridinov has made it clear that he sees the proposed procedure as a way for him to live on with a new and healthy body.

A different perspective would be that Spridinov is a head-donor rather than the recipient of a new body. He is donating his head to someone else who will live the rest of his life with Spridinov’s head but won’t be the same person as Spridinov. On this account, Spridinov is signing his own death warrant by volunteering for the surgery.

Despite the advanced science involved, the issues the proposed surgery raises aren’t new. Writing in the 17th century, English philosopher John Locke claimed that sameness of person is fundamentally a matter of mental continuity. He illustrated his point by means of a famous thought experiment: imagine that the soul of a prince, carrying consciousness of the prince’s past life, were to enter the body of a cobbler. Everyone can see, Locke contends, that the person with the cobbler’s body and the prince’s consciousness would be the prince and not the cobber. It would be just to punish this person for the prince’s past misdeeds but not the cobbler’s.

Locke’s view continues to be highly influential today, but it is assumed by most philosophers that the seat of consciousness is the brain rather than the soul. A modern variation on Locke’s example, devised by American philosopher Sydney Shoemaker, involves transplantation of the brain rather than the soul. If Mr Brown’s brain were transplanted into Mr Robinson’s de-brained skull, the resulting person – Shoemaker calls him Mr Brownson – would look like Robinson but would in fact be Brown as long as he is aware of Brown’s past as his own past.

Locke’s theory can be seen as justifying Spridinov’s view of Dr Canavero’s procedure. Spridinov’s head is where his brain is. Since his brain is the seat of his mental life, the person with Spridinov’s head and someone else’s body would be mentally continuous with Spridinov and so would be him.

However, there is no guarantee that things will turn out this way. Another possibility is that the surgery will wipe out Spridinov’s memories. The person who wakes from head transplant surgery might have no consciousness of Spridinov’s past and no sense of himself as Spridinov. If this were to happen Spridinov would no longer exist on Locke’s view. Instead, the surgery would bring into existence a new person who happens to have with Spridinov’s head.

Locke’s theory has recently come under fire from philosophers who call themselves “animalists”. They hold that each of us is a human animal, and the person who emerges from the surgery is the same person as Spridinov just as long as he is the same human animal as Spridinov. Unlike Locke, animalists think that this is a physical rather than a mental or psychological matter. Our mental lives can be disrupted without calling into question our continued existence.

Even from an animalist perspective, there is a case for saying that if any person wakes up from the surgery that person will be Spridinov. A human animal can arguably survive the loss of its limbs and most of its internal organs as long as its head and brain are kept alive and functional. The whole body isn’t required. For animalists, as for Locke, Spridinov might be right to think that he is being offered a new body rather than certain death. But sameness of person might be seen as being of little value without the mental continuity.

If what matters to Spridinov is mental continuity as well as having a healthy body then it will not be possible to determine whether the surgery is successful in these terms until after the event. The impact of head transplants on our mental lives remains unknown.

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Quassim Cassam is Professor of philosophy at University of Warwick.

This article was originally published on The Conversation.

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