Abstract
The neurophysiological footprint of brain activity after cardiac arrest and during near-death experience (NDE) is not well understood. Although a hypoactive state of brain activity has been assumed, experimental animal studies have shown increased activity after cardiac arrest, particularly in the gamma-band, resulting from hypercapnia prior to and cessation of cerebral blood flow after cardiac arrest. No study has yet investigated this matter in humans. Here, we present continuous electroencephalography (EEG) recording from a dying human brain, obtained from an 87-year-old patient undergoing cardiac arrest after traumatic subdural hematoma. An increase of absolute power in gamma activity in the narrow and broad bands and a decrease in theta power is seen after suppression of bilateral hemispheric responses. After cardiac arrest, delta, beta, alpha and gamma power were decreased but a higher percentage of relative gamma power was observed when compared to the interictal interval. Cross-frequency coupling revealed modulation of left-hemispheric gamma activity by alpha and theta rhythms across all windows, even after cessation of cerebral blood flow. The strongest coupling is observed for narrow- and broad-band gamma activity by the alpha waves during left-sided suppression and after cardiac arrest. Albeit the influence of neuronal injury and swelling, our data provide the first evidence from the dying human brain in a non-experimental, real-life acute care clinical setting and advocate that the human brain may possess the capability to generate coordinated activity during the near-death period.
Highlights
Near-death experience (NDE) has been reported in situations where the brain transitions toward death
We analyzed four time windows of interest: (1.) The interictal interval (II) window captures activity from 385 to 415 s after the clinical seizure. (2.) The left suppression (LS) window targets global spectral power from 510 to 540 s at the midpoint between suppression of left and bilateral hemispheric activity. (3.) The bilateral suppression (BS) window spans an interval between suppression of bilateral hemispheric activity and clinical cardiac arrest from 690 to 720 s. (4.) The final window includes the post-cardiac arrest period from 810 to 840 s at the midpoint between cardiac arrest and the end of the EEG recording
When bilateral hemispheric activity ceases, there is a temporary increase in absolute narrow- and broad-band gamma power, which declines after clinical cardiac arrest
Summary
Near-death experience (NDE) has been reported in situations where the brain transitions toward death. Subjective descriptions of this phenomenon are described as intense and surreal and include a panoramic life review with memory recalls, transcendental and out-of-body experiences with dreaming, hallucinations and a meditative state (Vanhaudenhuyse et al, 2007). Neural oscillations provide a temporal frame for information processing of perception, consciousness and memory during waking, dreaming and meditation (Llinás and Paré, 1991; Llinas and Ribary, 1993; Llinás et al, 1998; Lutz et al, 2004; Beauregard and Paquette, 2008; Fries, 2009). A similar inhibitory function has been suggested for delta band activity, which may suppress networks that are not essential for task accomplishment (Harmony, 2013). Memory flashbacks during recall of NDEs have been linked with oscillatory activity, similar to real life memory recall (Chawla et al, 2009, 2017; Palmieri et al, 2014)
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