If you think something through (make mind pictures or a movie of something), you open up a new path in the brain. This new path is a real path with real biochemical and electrical changes in the brain; the same as though you had done whatever it is that you practised in the mind. One could, therefore, also say that the brain does not distinguish between something that has happened and something which you have practised step-by-step and vividly in your mind.