Halcon: Then the brain, a very physical thing with all its chemical reactions, cannot be the ultimate determiner of which metaphysical phenomena is real or not.
I agree, but that isn't the point I was making. I am saying that, if thoughts and feelings are metaphysical, then the only source of metaphysics that we have been able to confirm is the brain. If there are other sources of metaphysics, we would need to identify them, and this would need to be corroborated. By definition, this cannot be done. Until we can confirm those other sources, the only one we can be sure of is the brain and the rest are conjecture.
Halcon: Good questions, if the brain can't, who or what makes the ultimate decision on wether something like desire, longing, melancholy is actually real?
Those would be emotions, which can be described as states of mind. Humans share many of these to such an extent that we can categorize them and recognize them in ourselves and others. I don't know about an ultimate decision, but it would be difficult to find people who do not experience these feelings in the same fashion.
Gods, on the other hand, do not share this consistency of experience and description. Across societies and nations, people can agree on how it feels to be happy or sad. Even animals seem to express these in a very consistent and similar fashion. Not so with deities. What might the difference be?