thesis

moved, so that the transplant takes. There would then appear to be two separate living per-
sons. Since both are controlled by hemispheres originating from the original person p,… we
would expect each publicly to affirm such apparent memories and to behave as if he had p’s
character… But they cannot both be p. For if they were, they would both be the same person as
each other, and clearly they are not—they have now distinct mental lives. The operation would
therefore create at least one new person–we may have our views about which (if either) resul-
tant person p is, but we could be wrong… However much we knew in such a situation about
what happens to the parts of a person’s body, we would not know for certain what happens to
the person.
This intriguing argument draws two potential replies. One may be brought out by an
analysis of the results of commissurotomy operations carried out during the 1960s and 1970s
as a last resort cure for chronic epilepsy (Sperry 1968). The operation involved severing the
corpus callosum bundle of 200 million nerve fibres linking the brain’s two hemispheres re-
sulting in an almost 9 complete lateral localisation of information processing.
Since language control ordinarily resides almost entirely in the left hemisphere, only the
left side of the brain can be directly interrogated about its phenomenology, which it claims it
continues to have. And there is a debate as to whether the right hemisphere should be con-
sidered a conscious subject too, which would imply that two streams of consciousness now
occupy a single human skull. Eccles’ view is as follows (1977, 326–8):
The rigorous testing of the subjects who have been subjected to section of the corpus callosum
has revealed that conscious experiences of the subject arise only in relationship to neural ac-
tivities in the dominant [left] hemisphere… We can regard the minor [right] hemisphere as
having a status superior to that of the non-human primate brain… It has many skills,… but it
gives no conscious experience to the subject… Moreover there is no evidence that this brain
has some residual consciousness of its own…
One can tell from Eccles’ wording (“it gives no conscious experience to the subject”) that
9 It is still possible for information to pass between the hemispheres by longer routes, such as via
the thalamus, hypothalamus or cerebellum.
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