I've had repeated NDE's consistently over the course of several years, due to my heavy experimentation with dissociatives. So I've pretty much seen it all, heaven and hell both. That's what led me to believe in the existence of the immortal soul.
It's not surprising that certain chemical events in the brain correspond to certain experiences of the soul. In fact, it's exactly what I'd expect. The body and spirit go together; you can't have one without the other. Even when your body dies, the physical elements of it remain because the cosmos as a whole remains--and at that point your soul is released from the limits of the body and you are brought into the presence of the divine (which is not necessarily a good thing, since evil people cannot cope with the presence of God).
Based on my experiences, I'd hypothesize that there are certain aspects of brain chemistry that are responsible for keeping the soul "tied" to the body, and that certain drugs or circumstances (such as NDE's) can cause those chemical "ties" to weaken, thus allowing Out-of-Body Experiences, or in the case of brain death, the final OBE, in which you don't come back!
The reason I think that the usual "scientific" model (which it ain't) of consciousness is wrong, the one that denies the existence of the soul, is that I've experienced access to knowledge I couldn't possibly have while out of the body. The closer I've ventured to death, the more of the mind of God I've encountered. There is some research into this (for instance, having people leave their body to remotely view an object out of their reach and then report back on it afterwards), but it's a difficult thing to subject to experiment. For those of us who have had the experiences, however, we'll remain convinced.