And God continues to live in the gaps...
(Not saying you are advocating the existence of an astral brain, but I'll comment anyway.) Invoking the existence of an astral brain seems a logical resolution to the issue if it can be proven that a) an astral plane exists and b) an astral brain can develop. However, creating a logically progressive explanation for some phenomenon or other doesn't make it factual, no matter how logical. Quantifiable proof for the existence of an astral brain (let alone an astral plane) would certainly be a swell addition to the science of neurology (and physics). Otherwise, we are left to conclude, based upon the available evidence, that conciousness does not leave the substance of the brain. As in Eos of Eons saying that without a brain we have no conciousness. That doesn't mean that conciousness cannot exist outside the physical structure of the brain, but the likelihood is, to the best of our knowledge, less probable than the more evidenced explanation.
And the God of the gaps lives on...