I have heard that some scientists think that some of the mental functions happen outside the brain.
But even so if the brain is damaged and it is the focal point of my personalty/spirit entery into the world then wouldn't that cause a severe personality change also? Also brain damage doesn't really account for personality change completely because it has to be there in the first place to come out, and people's personalities are more than just one sided.
It was also believed that the bumble be should not be able to fly, until someone realized that not everything was taken into account. We know so little about our bodies these don't even count as edcated guesses, even from a specialist.