Illustration by Hyunock Nam, NIH
When caring for patients on life support and in a comatose state, I would often question the types of thoughts they could be having. Were they able to hear me? Sense my touch? Dream or Imagine? Were they, in some way, aware of their surroundings? Despite being comatose and having no way to communicate their needs, we provided compassion, dignity and respect, trusting that our care might bring some measure of comfort. In the final moments, as their breathing slowed and the heart finally stopped beating, another deeper question arose: Does the brain fall into a period of silence immediately at the moment of death, or is there still some form of consciousness?
Researchers have discovered some new findings that indicate that there may be moments of brain activity during the process of dying/transition from life to death. In an article (Xu 2023) in the Proceedings of the National Academy of Sciences, it was reported that in select patients, there was a transient surge of organised bursts of electrical activity shortly after the cessation of life support (ventilator withdrawal), triggered by global hypoxia and intensifying with cardiac deterioration. These findings do not indicate that humans are consciously aware of anything or that they are reliving memories as they die; however, they do imply that the brain does not totally cease functioning at the same time the heart stops.
Death is most often defined as the irreversible loss of both circulation and brain function. For a long time, it was believed that as soon as the supply of oxygen to the brain ceased, the activity of the brain would also fade very quickly. But in previous studies using animals, there have been some unexpected results; they identified that there were temporary bursts of fast brainwaves(called gamma oscillations) that occurred shortly after cardiac arrest. These waves are normally linked to attention, memory and conscious thinking. This means that the brain is still functioning before someone dies.
In order to evaluate the possibility of the same thing taking place in humans, Xu and her co-authors performed an electroencephalogram (EEG) study on four patients who were in a coma and at the end of life in an intensive care unit. All four patients had had their EEG activity continuously monitored while life support was being maintained. With the consent of families, doctors continued recording as life support was withdrawn.
The authors of the study observed that in two of the four patients (both of whom had had a history of seizures), there were rapid and obvious bursts of gamma activity (>25 Hz, including gamma1 25-55 Hz and gamma2 80-150 Hz) shortly after cessation of the mechanical ventilator as the oxygen level of the patient dropped and cardiac deterioration occurred.
Additionally, the brainwaves in both of the patients did not reflect random brain activity; instead, they showed signs of coordination across different brain regions, including heightened local connectivity in the temporo-parieto-occipital (TPO) "hot zones" areas (associated with conscious processing) and increased global/interhemispheric connectivity (e.g., posterior brain regions with the prefrontal cortex), patterns similar to those waking states and dreaming. In addition, there was also enhanced cross-frequency coupling, where gamma waves were modulated by slower rates of oscillation (theta, alpha, beta, etc.).
Despite these findings, the authors noted that the EEG measurements cannot tell us what a patient may or may not have experienced at the time of death. Since neither of the two patients survived, it is impossible to tell if either of them was aware of their circumstances.
Dr George Mashour, co-author and anaesthesiologist at the University of Michigan, explained that while the brain “may remain active and coordinated during the transition from life to death,” this does not mean conscious experience is present. The rapid bursts of electrical activity that were observed in the two patients may simply reflect a response of the brain to extreme physiological stress or oxygen deprivation.
The authors of the research paper believe that these surges of gamma activity in brain regions associated with consciousness and senses (which can relate to out-of-body feelings in people with seizures) might help explain certain aspects of Near-Death Experiences (NDEs), such as some individuals' reports of vivid visual experiences or feelings of peace, reported by some after surviving cardiac arrest. But since the patients did not survive to share what they felt, there is no evidence these brain changes cause conscious experience, and the surges could just be the result of the brain responding to low oxygen or stress. So any connection to NDEs is speculative and requires more research.
Most experts agree that this study is small in size (only four patients, with surges observed in just two) and therefore must be interpreted carefully. However, the data support the growing concept that death may be more complex physiologically than previously believed.
The results of this study serve to emphasise to physicians and families who are facing decisions regarding end-of-life care to continue to support ethical research designed to enhance our understanding of the behaviour of the brain during the transition from life to death.
There are many aspects related to the neurologic implications of death which remain unknown; however, it appears very clear that death (neurologically) is not a sudden event but is rather a gradual process.
Reference:
Xu, G., Mihaylova, T., Li, D., Tian, F., Farrehi, P. M., Parent, J. M., Mashour, G. A., Wang, M. M., & Borjigin, J. (2023). Surge of neurophysiological coupling and connectivity of gamma oscillations in the dying human brain. Proceedings of the National Academy of Sciences of the United States of America. https://doi.org/10.1073/pnas.2216268120