Of course the brain states will be part of the picture, but if one of the many kinds of externalism or disjunctivism is correct, the bounds of the mental will extend far beyond the bounds of the brain.
And this shouldn’t be scary or worrying for physicalism, because physics is most likely blind to the boundaries of human bodies. If say, knowing that p has different causal efficacy than mere believing that p, then we should expect that the underlying causal story is not going to be merely a story of impingements on and effects of the brain. The type-type physicalist project should be updated to include these insights.
L. Miracchi