The near-death experience is a complex set of phenomena and a single account will not capture all its components. One recent theory is that the basic arousal systems beginning in the midbrain may account for many of the components of the near-death experience. Of interest is the locus coeruleus, a midbrain region involved in the release of noradrenaline. Noradrenaline is known to be involved in arousal related to fear, stress, and hypercarbia, and is highly connected to regions that mediate emotion and memory, including the amygdala and hippocampus. Indeed, stimulation of the noradrenaline system has been shown to enhance and consolidate memory, and plays a critical role in the sleep-wake cycle, including REM sleep. Along with basic midbrain systems, such as the periaqueductal gray, a region involved in opioid analgesia and basic fear responses, and the ventral tegmental area, which is a core dopamine reward area, the noradrenaline system may be part of a basic set of systems that directly or indirectly evoke positive emotions, hallucinations and other features of the near-death experience.
Taken together, the scientific evidence suggests that all aspects of the near-death experience have a neurophysiological or psychological basis: the vivid pleasure frequently experienced in near-death experiences may be the result of fear-elicited opioid release, while the life review and REM components of the near-death experience could be attributed to the action of the locus coeruleus- noradrenaline system. Out-of-body experiences and feelings of disconnection with the physical body could arise because of a breakdown in multisensory processes, and the bright lights and tunneling could be the result of a peripheral to fovea breakdown of the visual system through oxygen deprivation. A priori expectations, where the individual makes sense of the situation by believing they will experience the archetypal near-death experience package, may also play a crucial role. If one challenge of science is to demystify the world, then research should begin to test these and other hypotheses. Only then will discussion of near-death experiences move beyond theological dialogue and into the lawful realm of empirical neurobiology.
Friday, September 30, 2011
There is nothing paranormal about near-death experiences.
Mobbs and Watt argue that neuroscience can explain seeing bright lights, meeting the dead, or being convinced you are one of them, suggesting that there is nothing paranormal about these experiences. Instead, near-death experiences are the manifestation of normal brain function gone awry, during a traumatic, and sometimes harmless, event. They engage several basic features of near death experiences (awareness of being dead, out of body experiences, tunnel of light, meeting deceased people, euphoric emotions) and note the brain regions whose perturbation by electrical stimulation or ischemic strokes can induce each phenomenon. Some can be observed in normal individuals under particular conditions of sensory stimulation (I've done posts on the Blanke experiments on out of body experiences). Their arguments are of the "may be" or "could be" sort, and their summary seems to to be particularly vague hand waving...