During meditation, part of the parietal lobe, towards the top and rear of the brain, was much less active than when the volunteers were merely sitting still. With a thrill, Newberg and d'Aquili realised that this was the exact region of the brain where the distinction between self and other originates.
The limbic system is a part of the brain that dates from way back in our evolution. Its function nowadays is to monitor our experiences and label especially significant events, such as the sight of your child's face, with emotional tags to say "this is important". During an intense religious experience, researchers believe that the limbic system becomes unusually active, tagging everything with special significance.
So it seems that transcendental experience is all in internal metadata, and mystical experiences are just normal experiences with a "THIS IS IMPORTANT" bit set. Which makes sense.
And then there's Michael Persinger of Laurentian University, Ontario, who has developed a helmet that magnetically induces mystical experiences.
Through trial and error and a bit of educated guesswork, he's found that a weak magnetic field... rotating anticlockwise in a complex pattern about the temporal lobes will cause four out of five people to feel a spectral presence in the room with them... What people make of that presence depends on their own biases and beliefs. If a loved one has recently died, they may feel that person has returned to see them. Religious types often identify the presence as God. "This is all in the laboratory, so you can imagine what would happen if the person is alone in their bed at night or in a church, where the context is so important," he says. Persinger has donned the helmet himself and felt the presence, though he says the richness of the experience is diminished because he knows what's going on.
Of course, religious folks are not too keen on the idea that mystical experience is a purely physical phenomenon, and are quick to draw a distinction between "legitimate" mystical states and "illegitimate" ones (such as those induced by drugs or Dr. Persinger's magnetic helmet).