Much of life remains mysterious to even the greatest scientific minds, but what happens at the point of death is also shrouded in mystery. As you’d expect, researching the effects of termination on a person is fraught with difficulties, both practical and ethical, but a new study, published in the Annals of Neurology, provides some fascinating insights into the neurobiology of dying.
Not only do animal and human brains perish in a similar fashion, but there’s a noticeable period wherein restoring brain function is, hypothetically, possible. This reminds us that the ultimate aim of such work isn’t merely to peer into the final moments of a person’s life, but to understand how to save them from death at the very last moment.
This pioneering, first-of-its-kind study, by scientists working at Charité – Berlin University of Medicine and the University of Cincinnati, assessed patients who had suffered from “devastating brain injury” through various means, including horrific traffic accidents, strokes, and cardiac arrests. This resulted in the activation of a Do Not Resuscitate-Comfort Care order, followed by the withdrawal of any mechanical breathing apparatus.
Much of what we know about brain death in this regard comes from earlier studies conducted on animals throughout the 20th century.
The brain is deprived of oxygen as the body’s cardiovascular system grinds to a halt. A condition known as cerebral ischemia kicks in, wherein the lack of necessary chemical components leads to “complete electrical inactivity” in the brain.
This so-called cerebral silencing is thought to occur in order for the starving neurons to conserve their energy – in vain, if death is knocking. All-important ions leak from brain cells, as supplies of adenosine triphosphate – the compound that stores and transports energy around the body – run low.
Tissue recovery becomes impossible. “Massive, irreversible injury of these cells develops within <10 minutes when circulation completely ceases,” the team explain in their paper.
The team wished to know more about the specifics in humans, much of which remained enigmatic. With proper legal consent from the families of the patients – who weren’t necessarily going to die – the neurological activity of their brains were carefully monitored using a variety of electrode strips or arrays as events proceeded.
First, in 8-out-of-9 patients, the equipment picked up on the flaring of the brain cells as they tried to stop the inevitable. As this happens across the entire brain simultaneously without spreading gradually, it was termed a “nonspreading depression”.
This was then succeeded by a “spreading depolarization” (SD). Sometimes colloquially referred to as a “brain tsunami”, this involved a huge release of thermal energy as the electrochemical balances that keep brain cells alive and well break down, leading to their toxification and destruction. Then, as the patients’ oxygen levels drop precipitously, electrical activity is silenced across the brain.
Death washes over them, but, as their work revealed, it may one day not be as inevitable as it is now.
“Spreading depolarization marks the onset of the toxic cellular changes that eventually lead to death, but is not a marker of death per se, since depolarization is reversible – up to a point – with restoration of energy supply,” lead author Professor Jens Dreier, of Charité’s Center for Stroke Research, told IFLScience.
This paper’s data, then, demarcates the point at which cellular resurrection remains possible. There’s a lot more research to be done before this can become a reality, though: Dreier notes that SD is only just beginning to be understood. Like death itself, this neurological facet of it is a “complex phenomenon” for which “there are no easy answers”.