Where does the brain end and the soul begin? I figure that our brain is not what is giving us our agency, since it is subject to outside stimuli, such as medication. People do not choose their brain, so how can they be responsible for what the brain does? I think this is where the soul enters the picture. It should be a person’s soul that provides agency. It just seems to me, however, that one can control what the soul does by manipulating the brain. If someone takes depression medication, which balances the brain, which cause the person to commit less sin, is it really that person’s agency and/or soul that is the reason for this reduction of sin? Aren’t we therefore judged for the actions of our brain?
I think that some definitions would be in order at this point. We consider the brain to be the physical, material entity that harbors our thoughts, emotions, etc., and that provides subconscious control and regulation to all body processes and functions.
The mind is a non-material concept, which is the thought function of the brain. The mind includes stored information, concepts or ideas, emotions and feelings, and registers pain.
The soul is an entity comprised of the body and the spirit.
When a person dies, the brain, along with the rest of the body becomes lifeless and will decay with time. However, at death, when the spirit leaves the body, the mind accompanies it. The thinking part of a person existed with the pre-mortal spirit and continues to exist with the post-mortal spirit.
Now we must define agency. One definition of an agent is a person who acts for and in behalf of another, such as an insurance agent. The insurance agent, for instance, has authority to commit the company that he represents to the obligations of an insurance policy. In sports, a free agent, is a player who may contractually obligate himself to a team of his choice. He is, if you will, an agent unto himself.
In a religious setting a free agent is one responsible for his own behavior. So in a general sense, agency implies responsibility for action, words and thoughts.
The Lord said unto Enoch: Behold these thy brethre; they are the workmanship of min own hands, and I gave unto them their knowledge, in the day I created them; and in the Garden of Eden, gave I unto man his agency (Moses 7:32).
So man became responsible for his own actions when the Lord placed before him conflicting commandments that caused him to exercise his agency by choosing one or the other.
You are right in stating that our brain does not give us our agency. That responsibility for our own actions is given to us by God, to whom we are responsible for its use. We can damage the brain by ingesting drugs, for instance. We are then responsible for the thoughts and actions that brought such damage about, and we are responsible for the consequences of such actions.