Many people believe that a person is the brain or some part of the brain. You may be one of them. Paul Weiss writes this about the rapid change of the molecular particles that make up the brain cells.
“Recent studies on the turnover of the molecular population within a given nerve [brain] cell have indicated that ... their macromolecular contingent is renewed about ten thousand times in a lifetime.” [In other words, the matter making up each brain cell is completely renewed every three days.]
~Paul Weiss, “The Living System: Determinism Stratified,” in Arthur Koestler and J.R. Smythies, eds., Beyond Reductionism (London: Hutchinson, 1969), p. 13.
This means that your brain—that mass of matter which is contained in your skull today—is not the same brain that was in your skull last week.
The brain is used by the self; the brain is not the self. Of course, the brain is a very special part of the body—you, the self, use it to direct and control the rest of the body machine. It also serves to carry and process information coming from the different parts of the body and the external environment to you. But you are not your brain. You are the user of your brain.