What person X experiences is experienced by X’s gandhabba (mental body). Specifically, it is the hadaya vatthu of the gandhabba where thoughts are generated. That hadaya vatthu overlaps the heart (not in the heart).
In order to generate thoughts, the hadaya vatthu MUST first get a sense input from one of the six senses (five physical senses and the mana indriya that is located in the brain).
Therefore, if the brain in not active, the hadaya vatthu does not get any sense input, and thus cannot generate any thoughts.
When one is unconscious, one’s brain does not function. That is why one does not generate any thoughts while unconscious.
During deep sleep also parts of the brain are inactive. That is why we don’t generate thoughts during sleep, especially while in deep sleep called the REM state.
I have given an analogy to explain this in #8 and #9 of the following post:
“Our Mental Body – Gandhabba”
I see that the linking tool is not working. Here is the web address for that post: