The Near-Death Experience (NDE)
A scientific model of what happens in the brain in the moments before death
Posted May 3, 2017
Defining the near-death experience
NDEs are vivid and realistic, sometimes profound life-changing experiences reported by people who have been either physiologically close to death, as in cardiac arrest or other life-threatening medical conditions or emergencies, or by people who believed that death was imminent (Greyson 1999). The majority of persons who experience a life-threatening illness or injury do not report NDEs while a significant percentage—possibly the majority—of persons who report NDEs are never at risk of dying (Roberts & Owen 1988). Features commonly described by persons who report having NDEs include a sense of “being outside of one’s body,” profound feelings of peace, the feeling of “moving through” a dark tunnel, the sensation of “seeing” a bright light, experiencing a vivid review of life memories (the so-called “life review”), and “encounters” with deceased relatives, loved ones or supernatural beings. Although the same features are reported in many NDEs no particular feature is universally described by all NDE experiencers and each NDE is unique in terms of both the features it contains, the relative complexity of features, and the sequence or “pattern” in which visual imagery or other features are experienced or recalled. Near-death experiencers often report significant changes in values and beliefs, including increased spirituality, greater concern for others, a heightened sense of purpose and appreciation of life, and decreased fear of death.
New technologies are changing understandings of death and 'brain death'
Rapid advances in resuscitation, life-support, and functional brain imaging technologies are changing understandings of death and brain death, and providing new insights into neural mechanisms associated with minimally conscious states (MCS) and persistent vegetative states. These findings may help clarify neural mechanisms underlying near-death experiences (NDE) reported by persons who regain normal conscious functioning following brief or prolonged periods of loss of consciousness. Recent innovations in resuscitation technology that involve cooling the body to very low temperatures following cardiac arrest have significantly extended the viable limit of resuscitation, and, by definition, the threshold beyond which critical functions in the body and brain cannot be restored (Parnia & Young, 2013).
Decades of research have so far failed to resolve medical and philosophical questions pertaining to “brain death.” Currently accepted tests for determining brain death are based on measures of brainstem activity only, do not distinguish whole brain death from brainstem death, and are based on the findings of a single study published in the 1970s that have never been replicated. Subsequent studies have established that EEG activity continues in approximately 20% of “brain dead” patients (Grigg, Kelly, Celesia, Ghobrial, & Ross, 1987), brainstem evoked potentials remain in 5% (Faco, 2002), cerebral blood flow is detectable in 5% (Flowers & Patel, 2000), and pathologic destruction is not seen in at least 10% of cases where normal blood circulation has been maintained more than 24 hours after brain death (Schroder, 1983; Walker, Diamond, & Moseley, 1975). These findings imply that current methods used to ascertain brain death may not provide the information needed to confirm irreversible loss of all clinical function of the entire brain. This issue has direct bearing on near-death research since in the majority of persons who report near-death experiences it is not possible to measure brain function during a period of documented loss of consciousness.
A Surge in Brain Activity and Increased Brain-heart Coherence Take Place at Near Death
An important unanswered question is whether brain activity necessary and sufficient for complex conscious experience takes place at near death. Recent research findings using specialized EEG recording techniques and novel data analysis methods support that a surge of highly coherent brain electrical activity takes place in humans and rodents in the moments immediately before death. These findings also suggest that the mammalian brain is highly activated at near death as evidenced by the ordered release of neurotransmitters in multiple brain regions, and a previously unreported surge in neurophysiological coherence between the cortex and heart at multiple frequency bands in the final moments of life.
A Testable Neural Model of the Near-death Experience
Experiences that take place near death, in dreams, or in altered states retrospectively interpreted as NDEs reflect the activity of dynamically inter-connected networks involved in the generation, encoding, decoding, and interpretation of mental imagery. In a paper published in March, 2017 I proposed a multi-factorial model in which a variety of physiological or psychological factors result in the activation of dynamically inter-connected networks resulting in phenomenal content retrospectively interpreted as NDEs. According to the model physiological or psychological factors affect brain network activity until a critical threshold is reached resulting in the activation of releaser mechanisms.
Depending on specific physiological or psychological factors that ultimately activate inter-connected networks, and the degree to which two or more networks are coupled, disparate networks are more or less available to operate as potential releasers at different moments in time. Flexible coupling of dynamic networks results in a potentially unlimited number of unique permutations of NDE content, including mental imagery of greater or lesser emotional intensity or complexity, longer or shorter duration or apparent duration, and greater or lesser degrees of variation in features. The content of a unique NDE is determined by the properties of brain networks involved, modulatory effects of neurotransmitters on network activity, changes in brain electrical or metabolic activity, and changes in coherence relationships within or between discrete networks or groups of dynamically inter-connected networks within the brain and possibly also between the heart and brain (Borjigin et al., 2013; Li et al. 2015). Permutations of network activity that are more likely to occur because of a high degree of inter-connectivity may correspond to more frequently reported NDE features or recurring hierarchic sequences of features in response to traumatic experiences or during dreams or altered states of consciousness.
Lake, J. The Near-death Experience: A testable Neural Model, Psychol of Consciousness: Theory, Research and Practice March, 2017, http://psycnet.apa.org/index.cfm?fa=buy.optionToBuy&id=2016-45628-0014(1): 115-134.