This is in response to Matthew Apler's book The God Part of the Brain. In it he biologically explains spiritual experiences, and accurately so. However, he then makes the conclusion based on this that because a spiritual experience has a physical explanation, it has no truth to it.
If a psychological mechanism can exist to alter reality in order to increase the survival of an individual (as he argues is the purpose of the transcendental mechanism).
Then, the transcendenal mechanism may be an illusion.
and, the ego mechanism may be an illusion.
If the ego mechanism and the transcendenal mechansim are mutually exclusive.
It is impossible to determine if the transcendental reality is the illusion or if the ego reality is the illusion.
As for the experience itself is concerned.
There is no defnite way to dtermine if any experience has truth in itself because experiences are only within one's own realm of consciousness.
Thus, the explanation of a physical mechanism behind an epxerience cannot disqualify the truth of that experience.