http://www.wired.com/wiredscience/2013/04/consciousness-after-death/all/

Wired: Couldn’t the experiences just reflect some extremely subtle type of brain activity?

Parnia: When you die, there’s no blood flow going into your brain. If it goes below a certain level, you can’t have electrical activity.
It takes a lot of imagination to think there’s somehow a hidden area of your brain that comes into action when everything else isn’t working.

These observations raise a question about our current concept of how brain and mind interact. The historical idea is that electrochemical processes in the brain lead to consciousness. That may no longer be correct, because we can demonstrate that those processes don’t go on after death.

There may be something in the brain we haven’t discovered that accounts for consciousness, or it may be that consciousness is a separate entity from the brain.