The brain preserves the psychological values, memories and thoughts of a person. The brain theory claims that the two person stages belong to the same person if they are parts of a chain of psychologically continuous person stages, and if the same brain is involved. The idea that we can know who we are even without seeing our bodies supports brain continuity. In the case of Julia North, when the brain of Julia was transformed in the body of Mary Frances, Mary remembers Julia's experiences, her pain and sorrow and initially even has her personality. The fact that when the brain gets damaged the personality of the person undergoes a change proves that brain continuity is necessary for identity. The brain theory seems more plausible compared to the soul theory because the soul theory claims that "Same Soul Same Body", which might be the right argument but the concept of soul is so complicated that it is almost unexplainable. As compared to that the brain theory claims "Same Brain Same Body", which is not that difficult to explain as science has proved that there exists a brain in a human body. The memory theory does not seem appealing to me as I have this concept in mind that memories are part of the brains. Whenever we cannot remember something the first thought that runs in our mind is that something is wrong with our brains. The only reason that Mary Frances had the memories of Julia is because memories are associated with brains and she had the brains of Julia. There are thousands of incidents where people lose their memories because of brain damages or some complications in the brain. So I feel that memories, being part of the brain, the memory theory does not play an important role in identifying one's personal identity.
There are many objections to the brain theory that claim that brain continuity is not necessary for personal identity. One such argument is brain duplication where a duplicate of your brain is made which consists of exactly the same memories and same thoughts like you and is placed in the body of two other people, both of these person will be you but they would not be the same person, which is against the concept if brain continuity.
