One of the most widespread beliefs held by the religious concerns something called the soul
. As a concept, it spawns credulity in ghosts
, out-of-body experiences
, and incubuses
like Christianity's Holy Ghost. Literally, this concept haunts the human mind.
Is there any truth to these beliefs?
"If minds were leaving bodies, one would expect that there would be minds out of their bodies everywhere. You’d think that there’d be a mix-up occasionally and one or two souls or astral bodies would come back to the wrong physical bodies, or at least get their silver cords tangled up. One would expect some minds to get lost and never find their way back to their bodies. There should be at least a few mindless bodies wandering or lying around, abandoned by their souls as unnecessary baggage. There should also be a few confused souls who don’t know who they are because they’re in the wrong bodies." The Skeptic's Dictionary
Contrastingly, if minds weren't leaving bodies, we'd expect to see that phenomena like OBEs might be able to be induced by natural stimuli or pathological conditions of the brain.
And in fact, OBE-like experiences have been induced by stimulation of the brain. OBE-like experience has also been induced through stimulation of the posterior part of the right superior temporal gyrus in a patient. Positron-emission tomography (PET Scanning) was also used in this study to identify brain regions affected by this stimulation. (N Engl J Med. 2007 Nov 1;357(18):1829–33
In another study of OBEs occurring during near-death experiences, it was found possible to reliably elicit experiences similar to OBEs by stimulating the right temporal-parietal junction (TPJ; a region where the temporal lobe and parietal lobe of the brain come together). OBEs have been correlated with the presence of lesions in the right TPJ region and they can reliably be induced by electrical stimulation of this region in epilepsy patients. (Brain, 127(Pt 2), 243–258
; Nature, 419(6904), 269–270
And researchers have replicated OBEs using magnetic stimulation of the right temporal lobe of the brain, which is known to be involved in visuo-spatial functions, multi-sensory integration and the construction of the sense of the body in space. (Neuropsychiatric Practice and Opinion, 13(4), 521–522
Other contributing factors have been correlated to some degree. One that I'm particularly interested but needs more work is the possibility of low O2 or high CO2 levels in the brain during cardiac arrest, partially matching reports by people who have experienced gravity-induced loss of consciousness. The bottom line however is that while there isn't a comprehensive explanation for out-of-body experiences, these phenomena have been closely tied to the physiology of the brain's neurons. The corollary this is, if phenomena such as out-of-body experiences are all linked to the brain itself, then you cannot have a mind without a brain.
Yet belief in bodiless minds persists today and is even widespread, largely in the form of religion. Christianity alone is based largely upon it in the form of the Holy Ghost. Christians actually still believe that a spirit can exist, but can impregnate a woman. This was a common illusion up until the last hundred years ago from the general populace as well, with the spirit being referred to as an Incubus
. Since the beginning of the 20th century though, reports of incubi began being replace by reports of women claiming to have been impregnated during alien abductions. Why? Who knows. But you needn't worry: spirits, ghosts, incubi, and extraterrestrial rapists need not haunt you.