I see your point msharmony.
Consider that the brain is needed in order for it to gain experience and receive stimuli.
Without the brain first, no stimuli can be assessed to form an experience to register or act upon.
Your original query was
and does the behavior manipulate the brain or is the brain manipulating the behavior?
Consider this...
If someone that is very active and outspoken has a stroke that shuts down the brain's abilities their behavior changes no matter how ingrained it used to be.
A person that is in a brain dead coma has no behavior except to just lie there.
Amnesia victims have completely different behaviors while suffering memory loss.
Personally, I have behaved against my environment and conditioning as a willful choice. I see other people do it as well.
Think of the brain as a kind of computer in the sense that it has sensors and actuators.
It pulls in sensory data, processes it and sends out commands to the actuators.
The sensory data may be the same for all the computers(brains) in the area but the processing that initiates the commands to the actuators has differences. That is why one person may react differently to a similar environment or stimuli.
We are learning creatures. This means that we associate similar stimuli with previous actions. Experience is nothing more than memory. Behavior is the repetition of actions from memory based on reoccurring stimuli.
If new stimuli is sensed in a new environment the brain substitutes similar actions based on previous memory. If it works, the brain catalogs the stimuli/action protocol for future reference but if it doesn't work, the brain initiates new behavior attempting a desired outcome.
Even reflex is merely the sensor sending a signal to the brain and the body reacting to that stimuli.
If you touch a hot pan, you react by pulling your hand away. If your hand is numb and the nerves are unresponsive you will not pull your hand away until you sense the situation with another receptor. Which then, tells your brain to move your hand away.