Excerpted from The God Gene: How Faith Is Hardwired into Our Genes with permission of Doubleday.

What role does turning on one area of the brain and turning off another play in heightened spirituality and mystical experiences? When I described Newberg and d'Aquili's results to Gerald Edelman, he responded: "That's because a mystic is just a man trying to think like a dog." ...Edelman's theory holds that humans have two layers of mental life: core or primary consciousness, and secondary or higher consciousness. Core consciousness, the formation of scenes from sensory data, is evident in most animals, whereas secondary consciousness, which involves self-awareness, is, as far as we know, uniquely human. Thus, "thinking like a dog" is shorthand for a shift in the balance between primary and secondary consciousness. The part of the brain responsible for primary consciousness, according to Edelman, is the thalamocortical loop, consisting of the cortex and the thalamus-precisely the same area as the "attention association area" that showed increased activity in the Buddhist monks studied by Newberg and d'Aquili. With these ideas in mind, the SPECT scan results can be interpreted according to the following scenario. As the Buddhists meditate, they consciously attempt to clear their minds of thoughts and emotions. To do so, they send signals through the thalamus to the cortex, the seat of the will. As more and more of the brain's energy is directed toward this area, output to other regions is decreased through the process that neurobiologists call deafferentation. It would be like simultaneously turning on all the air conditioners in a house; the flow of power to the other appliances would be decreased. As more and more neural activity is directed to the thalamocortical loop, less and less is available for the orientation association area. The result was a loss of the usual sense of self and space that is conveyed by the posterior parietal lobes. As a result, the Buddhist meditators' brains could no longer tell where their bodies began and the outside world ended. They lost secondary consciousness even though primary consciousness-awareness-was normal or even heightened. Initially, this deafferentation evidence in the Buddhists was mild-a slight dreaminess. But as the meditation deepened and the power shortage became more acute, the orientation area began to send out SOS calls to the limbic system, thereby activating the cingulate gyrus. The limbic system, especially the hypothalamus, in turn called up the thalamocortical loop, telling it to find out what was going on-which made it work all the harder, resulting in even more deafferentation of the posterior parietal lobe. Soon the neural phones were buzzing off the hooks with back-and-forth calls about the emergency situation in the orientation association area. Ironically, each call made the situation even more serious as the wires became more and more overloaded. As Newberg and d'Aquili elegantly describe the situation, "A reverberating circuit is established in the brain, with a stream of neural impulses gathering strength and resonance as they race again and again along their neural speedway, fostering deeper and deeper levels of meditative calm with every pass." This is how the Buddhist meditators were able, in Edelman's more prosaic words, to "think like dogs." By focusing all of their mental energy on primary consciousness, they decreased their secondary consciousness to the point of losing the usual sense of self. They became one with the world and the world became one with them-all through the redirection of a few nanovolts of electrochemical energy.

The effects of spiritual activity on the brain are not limited to Buddhist meditators. Newberg and d'Aquili have also used SPECT imaging to study Franciscan nuns immersed in prayer and observed very similar changes in their scans. The main difference was that the sisters described their peak moment as a "tangible sense of the closeness of God and a mingling with Him," rather than as a "Ztt" experience like the Buddhists. Although SPECT has never been used on Muslims at Mecca or Jews at the Western Wall, it is likely that their brains go through similar changes.