Anyway, if "qualia" are brain states, then the question "how do qualia depend on brain states" is trivially answered.
It still makes sense to ask what these "brain states" actually are, physically. Since we seem to have direct experiential access to them as part of our subjective phenomenology, this suggests on Occamian grounds that they should not be as physically or ontologically complex as neurophysical brain states. The alternative would be for biological brains to be mysteriously endowed with ontologically basic properties (as if they had tiny XML tags attached to them) which makes no sense at all.
It still makes sense to ask what these "brain states" actually are, physically
I would agree that it makes sense to ask what sorts of brain states are associated with what sorts of subjective experiences, and how changes in brain states cause and are caused by those experiences, and what sorts of physical structures are capable of entering into those states and what the mechanism is whereby they do so. Indeed, a lot of genuinely exciting work is being done in these areas by neurologists, neurobiologists, and similar specialists as we speak.
[Cross-posted.]
1. Defining the problem: The inverted spectrum
A. Attempted solutions to the inverted spectrum.
B. The “substitution bias” of solving the “easy problem of consciousness” instead of the “hard problem.”
2. The false intuition of direct awareness
A. Our sense that the existence of raw experience is self-evident doesn’t show that it is true.
B. Experience can’t reveal the error in the intuition that raw experience exists.
C. We can’t capture the ineffable core of raw experience with language because there’s really nothing there.
D. We believe raw experience exists without detecting it.
3. The conceptual economy of qualia nihilism pays off in philosophical progress
4. Relying on the brute force of an intuition is rationally specious.
Against these considerations, the only argument for retaining raw experience in our ontology is the sheer strength of everyone’s belief in its existence. How much weight should we attach to a strong belief whose validity we can't check? None. Beliefs ordinarily earn a presumption of truth from the absence of empirical challenge, but when empirical challenge is impossible in principle, the belief deserves no confidence.