The brain is the central processing unit of the body and plays a key role in translating the content of the mind (your thoughts, feelings, attitudes, beliefs, memories and imagination) into complex patterns of nerve cell firing and chemical release. These complex patterns of nerve cell firing and chemical release are called neurosignatures, and they intimately affect the physiology and biochemistry of the body.
When your personality starts, when you come into being, the mind also comes into being, because you are the mind itself. The one who is speaking to me just now is the mind speaking, and it originates the moment the Mr. so-and-so that you are originates. When did you originate? How did you come into being?