Fascination with near-death experiences, often featuring white light, encounters with deceased loved ones and auditory phenomena, has permeated our cultural consciousness. The prevalence of these shared elements has prompted researchers to explore the possibility that a form of consciousness persists even after cardiac function has ceased.

A link to consciousness
The journal Proceedings of the National Academy of Sciences recently published a study offering the suggestion that a burst of activity in the brain during its final moments may be linked to consciousness.

University of Michigan Associate Professor Jimo Borjigin spearheaded the research, which built upon animal studies conducted approximately a decade earlier in partnership with George Mashour, the founder and director of the Michigan Center for Consciousness Science.

Studies in animals and humans detailed comparable surges of gamma brain waves after experiencing oxygen deprivation due to cardiac arrest. Mashour noted that the study provided valuable insights into the neurophysiological mechanisms underlying such phenomena. “How vivid experience can emerge from a dysfunctional brain during the process of dying is a neuroscientific paradox,” he added.

The researchers examined four hospital patients who succumbed to cardiac arrest while in a comatose state and under EEG monitoring. After receiving permission from the patients' families, the individuals were taken off life support.

Two of the patients exhibited a surge in gamma wave activity – a rapid brain signal associated with consciousness – and an increased heart rate upon the removal of ventilator support. The activity was detected in the brain's "hot zone," an area implicated in dreaming, epilepsy-related visual hallucinations and altered states of consciousness. This area is found at the intersection between the occipital, parietal and temporal lobes...

Brain function around the time of cardiac arrest is poorly understood. While the loss of overt consciousness is invariably associated with cardiac arrest, it is unclear whether patients can possess covert consciousness during the dying process. Near-death experiences (NDE) (1), reported to be highly lucid, “realer than real,” and common to people from diverse cultural and religious backgrounds (2, 3), have been described by 10 to 20% of cardiac arrest survivors (2–4). Indeed, it has been claimed (3, 5) that these episodes occur during clinical death even during electrical quiescence of the electroencephalogram (EEG). NDE represent a biological paradox that challenges our fundamental understanding of the dying brain, which is widely believed to be nonfunctioning under such conditions.

Elevation of high-frequency oscillations, a candidate marker of consciousness (6), has been reported previously in patients dying from critical illnesses (7–9). In healthy animals, our group reported that sudden termination of cardiac function or acute asphyxia stimulated high levels of gamma activities, including a global increase of functional and directed connectivity in gamma oscillations (10, 11). To date, however, no studies have reported neural correlates in dying humans that might account for the subjective percepts reported by near-death experiencers (1, 3, 12). The goal of this study was to identify neural correlates of the dying process.

Visual consciousness is classically associated with two distinct streams: the ventral stream coursing through the occipitotemporal (OT) junction that mediates visual object recognition, and the dorsal stream coursing through the occipitoparietal (OP) junction that serves nonconscious visually guided actions (13). A part of the dorsal stream also projects to the medial temporal lobe flowing through the temporoparietal (TP) junction mediating visuospatial processing (13). Importantly, visual sensations can be elicited by the stimulation of both occipital and parietal cortices in the absence of an external visual stimulus (14), and both temporal and parietal cortices function as early gatekeepers of perceptual awareness (15). Thus, activation of the temporo–parietal–occipital (TPO) junctions provides a key gateway for visuospatial processing in normal human brain (13). Critically, during dreaming, high-frequency activity within posterior cortical areas has been shown to predict perceptual content experienced by healthy subjects (16). Because this posterior cortical zone activated in dreaming (16) largely overlaps with that identified in waking (13), the TPO junctions are considered a “hot zone” for the neural correlates of consciousness (6). Internal perception of bright light or familiar faces reported by survivors of clinical death (3) suggests a preserved capacity in the dying brain to process internally generated vision. It remains to be determined if the posterior cortical regions are activated in the dying human brain.

These findings prompted us to investigate the neural activity of the brain in the dying patients before and after clinical withdrawal of ventilatory support. Specifically, we examined EEG signals, by applying the computational tools used in our previous study of dying animals (10), with a focus on the following features: temporal dynamics of EEG power, local and long-range phase-amplitude coupling between low- and high-frequency oscillations, and functional and directed cortical connectivity across all frequency bands. All analyses were conducted with close attention to parallel changes of electrocardiogram (ECG) signals, as reported previously...