Back in 2018, researchers were able to study the moment brain death becomes irreversible in the human body for the first time, observing the phenomenon in several Do Not Resuscitate patients as they died in hospital.

For years, scientists have researched what happens to your brain when you die, but despite everything we've found out, progress has been stymied by an inability to easily monitor human death – since physicians are conventionally obliged to prevent death if they can, not monitor it as it takes hold.

What this means is most of our understanding of the processes involved in brain death come from animal experiments, strengthened with what we can glean from the accounts of resuscitated patients disclosing their near-death experiences.

But in 2018, an international team of scientists made a breakthrough.

In animals, within 20 to 40 seconds of oxygen deprivation, the brain enters an 'energy-saving mode' where it becomes electrically inactive and neurons cease communicating with one another.

After a few minutes, the brain begins to break down as ion gradients in cells dissipate, and a wave of electrochemical energy – called a spreading depolarisation (or 'brain tsunami') spreads throughout the cortex and other brain regions, ultimately causing irreversible brain damage.

But a team led by neurologist Jens Dreier from Universitätsmedizin Berlin in Germany – who monitored these processes taking place in nine patients with devastating brain injuries (under Do Not Resuscitate – Comfort Care orders) – say the tsunami of brain death may actually be capable of being stopped.

"After circulatory arrest, spreading depolarisation marks the loss of stored electrochemical energy in brain cells and the onset of toxic processes that eventually lead to death," Dreier explained at the time.

"Importantly, it is reversible – up to a point – when the circulation is restored."

Using neuro-monitoring technology called subdural electrode strips and intraparenchymal electrode arrays, the researchers monitored spreading depolarisation in the patients' brains, and they suggest it's not a one-way wave – as long as circulation (and thus oxygen supply) can be resumed to the brain.

"Anoxia-triggered [spreading depolarisation] is fully reversible without any signs of cellular damage, if the oxidative substrate supply is re-established before the so-called commitment point, defined as the time when neurons start dying under persistent depolarisation," the authors explained in their paper.

For patients at risk of brain damage or death incurred through cerebral ischemia or other kinds of stroke, the findings could one day be a life-saver, although the researchers explain a lot more work is needed before physicians will be able to take advantage of these discoveries.

"There are no direct implications for patient care today," Dreier said, pointing out more observations will be essential to understand what's really going on here.

"Knowledge of the processes involved in spreading depolarisation is fundamental to the development of additional treatment strategies aimed at prolonging the survival of nerve cells when brain perfusion is disrupted."

The findings were reported in Annals of Neurology.

A version of this article was first published in March 2018.