Continuous electroencephalography (EEG) recordings revealed the human brain may be capable of generating coordinated activity during the transition period to death, even after the suppression of neuronal activity in both hemispheres following cardiac arrest, according to research published recently in Frontiers in Aging Neuroscience.
Following cardiac arrest and during near-death experience (NDE), there is a lack of understanding of the neurophysiological processes in the dying human brain. Experimental animal studies have shown increased gamma-band activity following cardiac arrest, but to date, no studies have investigated this in humans.
Subjective descriptions of the NDE sometimes include memory-recalled panoramic life review. “It is hypothesized that the brain may generate a memory replay within this ‘unconscious’ phase with an increase in oscillatory activity,” the researchers stated.
The objective of this study was to report on the first continuous EEG recording from the human brain in the transition phase to death.
The current study was a case report of an 87-year-old male presented to the emergency department after falling. The patient had a Glasgow Coma Scale (GCS) of 15, but his score quickly declined to 10 as he experienced anisocoria, an unequal pupil size, and a bilateral reaction to light.
Computerized tomography (CT) scans helped confirm the patient experienced bilateral acute subdural hematomas (SDH). A left decompressive craniotomy was performed to remove the hematoma. After 2 days of remaining stable in the intensive care unit, EEG showed the patient continued to decline due to non-convulsive status epilepticus in the left hemisphere.
Following, the EEG showed a burst suppression patterns over both hemispheres along with ventricular tachycardia with apneustic respirations and clinical cardiorespiratory arrest. This led the patient’s family to sign a “Do-Not-Resuscitate (DNR),” which stopped further treatment until he passed away.
The researchers analyzed 4 time windows of interest during the transition period to death: The interictal interval (II) — 385-415 seconds after clinical seizure; The left suppression (LS) window — 510-540 seconds between suppression of left and bilateral hemispheric activity; The bilateral suppression (BS) window — 690-720 seconds where the bilateral hemispheric activity ceased and clinical cardiac arrest occurred; and The post-cardiac arrest (post-CA) period — 810-840 seconds between cardiac arrest and the end of the EEG recording.
“Spectral analysis revealed a surge in absolute gamma power after suppression of neuronal activity in both hemispheres, followed by a marked decrease after cardiac arrest,” the researchers noted.
Notably, a decrease in delta brainwaves was observed between the II and LS window, which declined even more following the post-CA window. Between LS and BS time windows, delta activity declined at 42% and 27.6%, respectively. Delta brainwaves did experience a mild increase of 37.3% during the post-CA time window.
Researchers said these findings suggest that, “an intricate interplay between low- and high-frequency bands takes place after gradual cessation of cerebral activity and lasts into the period when cerebral blood flow is ceased (post cardiac arrest).”
Several case study limitations were noted: the patient’s post-traumatic brain suffered hemorrhage, swelling, and seizures possibly influencing brain activity; anesthesia-induced loss of consciousness altering neuronal oscillations; dissociative drugs and psychosis linked to a surge in gamma synchronization; significant doses of anticonvulsant medication; asphyxia and hypercapnia; no EEG baseline was recorded for comparison; it is unknown if stereotyped neuronal activity patterns are conserved during the transition phase to death.
The human brain may engage a series of stereotyped activity patterns during death.
“Given that cross-coupling between alpha and gamma activity is involved in cognitive processes and memory recall in healthy subjects, it is intriguing to speculate that such activity could support a last ‘recall of life’ that may take place in the near-death state,” the researchers concluded.
Vicente R, Rizzuto M, Sarica C, et al. Enhanced interplay of neuronal coherence and coupling in the dying human brain. Front Aging Neurosci. Published online February 22, 2022. doi:10.3389/fnagi.2022.813531