In his controversial 1976 book, The Origin of Consciousness in the Breakdown of the Bicameral Mind, Julian Jaynes, a Princeton psychologist, argued that the brain activity of ancient people - those living roughly 3,500 years ago, prior to early evidence of consciousness such as logic, reason, and ethics - would have resembled that of modern schizophrenics.

Jaynes maintained that, like schizophrenics, the ancients heard voices, summoned up visions, and lacked the sense of metaphor and individual identity that characterizes a more advanced mind. He said that some of these ancestral synaptic leftovers are buried deep in the modern brain, which would explain many of our present-day sensations of God or spirituality. [via, img]