It depends on who you ask and how they view the concept of dreaming.

Some will say dreaming occurs on another plane of existence others say it's simply inside the brain. But that old argument goes way back to the basic idea of the afterlife and consciousness being interdependent from the body.

In my honest opinion and from barebones research (really all thats currently available) it is suggestable that a OBE is simply a different form of transition into the dream state. Most OBE'rs don't transition into the dream like normal WILD dreamers, most likein Raduga book will use some form of phantom wiggling or imagined movement, whereas note most WILD'ers will use things like Mnemonic or Visualization.

I believe that this difference in technique stimulates different areas of the brain, of course it would have to use different areas. Visualization comes from different areas of the brain then say Proprioception (the sensation of the body moving) this much is obvious. But when it comes to dreaming we also know that Lucid Dreamers have greater activity in areas of their brain that Non-LDers do, which would be as expected. Most research cites increase beta wave activity in the frontal lobe, among other places that see to corrospond to areas previously believed to be responsible for consciousness.

We know it's possible for the visual part of a dream to form without a dreamer, I suggest the reverse is true aswell, in that it's possible for the dreamer to decouple from reality but to have no visual. Note again that the former tends to occur with visualization techniques and the latter with phantom wiggling. Such an event would likely cause the brain to compensated by drawing reality as it would immediately assume it is still awake.