A fascinating experiment in neurotheology where Dr. Michael Persinger of Laurentian University, Canada put an apparatus on people's heads to stimulate the temporal lobe.
The temporal lobe is active when people experience what they term as 'spiritual experiences' - increased sensitivity correlates to increased religious tendencies, and generally, the more intense an experience, the more sensitive one's temporal lobe.
Persinger introduced a current into the temporal lobe of this 'helmet', which participants reported as a feeling that someone was next to them in the room. Richard Dawkins, professor at Oxford and famed atheist (writer of The God Delusion), famously, did not experience anything, and scored very low on a scale of temporal lobe sensitivity. People with temporal lobe epilepsy are prone to these kind of experiences.
Scientific American, October 2007 - "Searching for God in the Brain" - http://www.sciam.com/article.cfm?id=searching-for-god-in-the-brain&print=true
Persinger, M.A. "Religious and mystical experiences as artifacts of temporal lobe function: a general hypothesis." Percept Mot Skills. 1983 Dec;57(3 Pt 2):1255-62