The difficulty with the theory of the subject is that one can speculate about it in three very different ways.   The clinical approach, whether psychoanalytic, behavioral or Jungian-mystical, entails observing and interpreting symptoms, projections and so on.  The neurobiological approach seeks to understand what's happening in the physical substrate.  And then there are speculative approaches - what kind of thing (or non-thing) is the subject, are there other types of subject in nature, is the subject basically isomorphic with computation and so on