You might find the quote from my post over here: Where is the line drawn between manifestations of belief and accepted root assumptions? - #23 by Christopher helpful, Doreen.
I’ll re-quote it here:
In somewhat the same manner, your physical brain is a doorway that triggers activity in your mind. Your beliefs then are largely responsible for the areas of the brain that you activate, and for the resulting nonphysical action of the mind.
Session 671, Chapter 20, The Nature of Personal Reality
This particular excerpt was actually pretty eye-opening for me in helping me understand the mind/brain relationship… which helped me with my original struggle from that topic.
The beliefs (mind) can affect the brain, which then once more affects the mind.