Near-death experiences (NDEs) have long captivated human curiosity, blending the boundaries between science, spirituality, and philosophy. These profound episodes, often reported by individuals who have faced life-threatening situations, are characterized by vivid visions, feelings of peace, and out-of-body experiences. A groundbreaking study published in Nature Reviews Neurology by researchers from the University of Liège, led by Šarlotė Maršal (angl. Charlotte Martial), offers a comprehensive neuroscientific model to explain the complex interplay of psychological and physiological processes behind NDEs. This article delves into the mechanisms driving these experiences, exploring neurotransmitter activity, brain network changes, and evolutionary perspectives, while addressing their implications for understanding consciousness.
What Are Near-Death Experiences?
Near-death experiences are episodes of altered consciousness that occur during critical physiological crises, such as cardiac arrest, severe trauma, or extreme hypoxia. Individuals often report a range of phenomena, including:
- Seeing a bright light or tunnel
- Experiencing out-of-body sensations
- Feeling profound peace or euphoria
- Encountering deceased loved ones or spiritual entities
- Reviewing one’s life in a panoramic memory
These experiences, while deeply personal, share common features across cultures and contexts, suggesting a universal underlying mechanism. The study by Šarlotė Maršal (angl. Charlotte Martial) and colleagues, including Paulina Fritz and Olivia Gosseries, proposes that NDEs arise from a cascade of neurophysiological and psychological processes triggered by life-threatening conditions.
The Neuroscientific Model of NDEs
The research introduces the Neurophysiological Evolutionary Psychological Theory Understanding Near-Death Experience (NEPTUNE) model, which integrates findings from neuroscience, psychology, and evolutionary biology. This model posits that NDEs result from a combination of:
- Neurophysiological Changes: Alterations in brain activity, neurotransmitter release, and cerebral blood flow.
- Psychological Processes: Cognitive and emotional responses, including dissociation and top-down processing.
- Evolutionary Mechanisms: Survival strategies rooted in phylogenetically preserved threat responses.
Neurophysiological Mechanisms
During critical conditions like cardiac arrest, the brain undergoes significant stress due to impaired cerebral blood flow, leading to systemic hypotension, hypoxia, and hypercapnia. These conditions cause:
- Hypoxia and Hypercapnia: Reduced oxygen and elevated carbon dioxide levels result in acidosis, altering brain pH and neuronal excitability (Hansen, 1985).
- Neurotransmitter Dysregulation: A surge in key neurotransmitters, including serotonin, dopamine, glutamate, norepinephrine, GABA, acetylcholine, and endorphins, activates specific neural circuits.
- Neuronal Hyperexcitability: Increased excitability in brain regions like the temporoparietal junction and visual cortex contributes to vivid perceptions (Blanke & Arzy, 2005).
Role of Serotonin
Serotonin plays a pivotal role in NDEs, particularly through its interaction with 5-HT1A and 5-HT2A receptors. The activation of 5-HT2A receptors, also implicated in psychedelic experiences, may explain the hallucinatory aspects of NDEs, such as tunnels of light or encounters with spiritual entities (Timmermann et al., 2018). Serotonin’s calming effects, mediated by 5-HT1A receptors, may contribute to the profound peace reported by experiencers (Carhart-Harris & Nutt, 2017).
Glutamate and NMDA Receptors
Glutamate, a primary excitatory neurotransmitter, interacts with NMDA receptors, which are critical for synaptic plasticity and memory formation. Dysregulation of glutamate during hypoxia may mimic the effects of dissociative drugs like ketamine, contributing to out-of-body experiences and altered self-perception (Jansen, 1989).
Norepinephrine and Emotional Arousal
Norepinephrine, released during stress, enhances memory consolidation and emotional arousal. This may explain why NDE memories are vivid and enduring, even in clinically unconscious states (McGaugh, 2004).
Endorphins and Euphoria
Endorphins, released during extreme stress, contribute to feelings of euphoria and pain suppression, aligning with the serene and blissful sensations reported in NDEs (Sotelo et al., 1995).
Psychological Mechanisms
From a psychological perspective, NDEs are influenced by top-down processes, where cognitive expectations and prior beliefs shape the experience. Dissociation, a state of disconnection from one’s body or reality, is a key feature, potentially serving as a coping mechanism during life-threatening situations (Greyson, 2000). Non-pathological traits like fantasy proneness may also amplify the intensity of NDEs (Martial et al., 2018).
Evolutionary Perspective
The NEPTUNE model suggests that NDEs may have evolutionary roots as a survival mechanism. In situations where fight-or-flight responses are not viable, the brain may enter a dissociative state, akin to thanatosis (playing dead) observed in animals. This state, mediated by serotonin and other neurotransmitters, reduces pain perception and promotes psychological resilience, potentially aiding survival in extreme conditions (Peinkhofer et al., 2021).
Brain Activity During NDEs
Studies on the dying brain reveal surges of electrical activity, particularly gamma oscillations, which are associated with heightened consciousness and interhemispheric connectivity (Borjigin et al., 2013). These surges, observed in both human and animal models, occur even in states of clinical unconsciousness, suggesting that the brain remains highly active during the dying process (Xu et al., 2023).
EEG Signatures and Consciousness
Electroencephalogram (EEG) studies during cardiac arrest and syncope-induced unresponsiveness show patterns resembling REM sleep, characterized by frontal-parietal beta-theta networks (Martial et al., 2024). These findings align with the entropic brain hypothesis, which links increased brain activity complexity to expanded consciousness (Carhart-Harris, 2018).
Comparative Insights: Psychedelics and NDEs
The phenomenological similarities between NDEs and psychedelic experiences, particularly those induced by DMT or psilocybin, provide valuable insights. Both states involve ego dissolution, vivid imagery, and mystical sensations, likely driven by serotonin 2A receptor activation (Timmermann et al., 2018). Research on endogenous DMT, a hallucinogenic compound, suggests its potential role in NDEs, though its presence in the human brain remains debated (Dean et al., 2019).
Implications for Consciousness Research
NDEs offer a unique window into the nature of consciousness, particularly in near-death states before brain death. The persistence of vivid experiences during clinical unconsciousness challenges traditional views of consciousness as solely dependent on intact brain function. The NEPTUNE model supports theories like integrated information theory, which posits that consciousness arises from complex neural interactions (Koch et al., 2016).
Challenges and Future Directions
Studying NDEs poses methodological challenges, including the retrospective nature of reports and variability in clinical conditions. Future research should focus on:
- Real-time neuroimaging during critical states
- Standardized scales, such as the NDE-C scale, for quantifying experiences (Martial et al., 2020)
- Cross-species studies to explore evolutionary mechanisms
Interdisciplinary approaches combining neuroscience, psychology, and philosophy will be crucial for unraveling the mysteries of NDEs.
The neuroscientific model of near-death experiences presented by Šarlotė Maršal (angl. Charlotte Martial) and colleagues marks a significant step toward demystifying these profound phenomena. By integrating neurophysiological, psychological, and evolutionary perspectives, the NEPTUNE model offers a comprehensive framework for understanding NDEs. As research progresses, these insights may not only illuminate the mechanisms of NDEs but also deepen our understanding of consciousness itself.