Consider the following two scenarios happening to the same person.

1) Two people come to the door and inform them that they have won a cruise. Six months later they are on a ship and having a great time.

2) Two terrorists come to the door and kidnap them. Six months later they are in a foreign prison and are feeling depressed.

If a medical researcher measured the brain chemicals of the person in both situations, they would would see in the second case what medical people usually refer to as a chemical imbalance.

But what created the differences was what they thought or felt about the situation they were in. Your beliefs affect your thoughts which affect your feelings. You are constantly creating your next moment, which then becomes the present, then the past. Each moment can be a reaction to a past incident, or a creation of a new response.

People who think that the brain creates thought have it backwards. You, as a spirit, are creating your mind using the brain a switchboard. And ultimately all matter is created moment to moment by all the spirits in this universe.