Do Our Brains Replay Our Most Important Memories as We Die?

In February 2022, a surprising new study provided a never-before-seen view into the dying brain.

An unusual medical case report recorded for the first time the brain activity of a patient before, during and after a cardiac arrest. The study’s authors made a connection between these characteristic activity patterns, the accounts of people who have undergone near-death experiences (NDEs) and wider neuroimaging studies to hypothesize that the brain activity might be indicative of a “last recall” of a life’s memories. Let’s take a deep dive into these findings.

An unusual case study

Perhaps the oddest thing about the paper’s analysis of brain activity before and after death is that it has never been done before. “I was also very, very surprised when the neurosurgeon contacted me and told me, look, I have these recordings, and we think they are unique,” says Dr. Raul Vicente, head of the computational neuroscience lab at the University of Tartu and a co-author on the study.

Vicente is a physicist by training but has spent the last 15 years working with neuroscientists, an arrangement that meant he was picked out by Dr. Ajmal Zemmar, a neurosurgeon based at the University of Louisville who treated the patient, to analyze the data.

When we consider the unusual circumstances around the end of the patient’s life, Vicente says, it’s easier to understand why the study’s data is unique. The 87-year-old patient involved had been admitted to hospital, where he exhibited tremors and twitches that were possible signs of status epilepticus – a long-lasting seizure that can cause permanent brain damage and death. To ascertain in more detail what was going on in the patient’s brain, Zemmar’s team wired the patient up to an electroencephalography (EEG) rig. Electrodes were placed across the patient’s scalp in a classic “10-20 system” arrangement that assures equal spacing of electrodes. During the EEG recording process, the patient went into cardiac arrest.

After consulting with the patient’s family and noting his do not resuscitate (DNR) status, no further treatment was given to the patient, who then passed away.

In virtually any other clinical situation, there would be little reason to attach a full EEG rig to a dying patient, meaning the only existing comparable data comes from more limited EEG data recorded from patients in palliative care. The full setup used in Vicente and colleagues’ study is unique in its depth and its recording of the last minutes of a person’s life.

The why and how of brain activity

The researchers’ next task was to analyze this one-of-a-kind dataset. The main feature of the data, says Vicente, was an increasing level of gamma wave activity in the moments before the patient went into cardiac arrest. Vicente is also first to say that, with a sample size of just one, the rest of the study’s conclusions must necessarily rely on other sources of information.

Of the brain activities that involve a spike of gamma activity, Vicente notes, “one of them is storage of information or recall of information or memories.” Our ability to tie such cognitive activities to particular brain waves comes from decades of electrophysiology work that has built up a picture of what brain activity does during, for example, behavioral tasks, even if the why or how of these signatures remains unclear.

But death is, by definition, both a once-in-a-lifetime event and one that offers little chance for post-game analysis or feedback. Luckily, however, there is a wide pool of evidence from individuals who have approached death’s door without passing through.

Exploring near-death experiences

These are people who have undergone near-death experiences (NDEs). “What is consistently reported,” says Vicente, “is that these patients also have flashbacks of memory. They recollect important experiences in their lives.”

As opposed to the current study’s as-low-as-it-goes n number, there are thousands of data points from people who were interviewed after, for example, being resuscitated post-cardiac arrest. “Around 10-20% of people who undergo NDEs report this flashback of memories and recollection or recall of life experiences or family,” Vicente adds.

Vicente says that, by putting these different strands of evidence together, one might hypothesize that the increase in gamma activity is the “neurophysiological substrate” of the experience of people who have NDEs.

What the study may provide is one of the few glimpses we will ever get into the last seconds of the brain’s function. A brief, yet vivid window into the highs and lows of existence, which squeezes decades into seconds and allows the mind to view the landscape of life from a final peak perspective.

But that’s just one interpretation.

The limitations of understanding the brain

What the study highlights on a deeper level are the limitations of the tools we currently use to analyze the data our brains produce. While gamma activity may increase during recall, it is also increased by other cognitive activities, so we can only speculate that memory recall is what the dying patient’s brain was doing.

That’s even assuming the gamma increase was due to cognitive changes. Vicente mentions that the paper highlights several different possible confounding factors in their study alone that could have influenced their findings – perhaps the patient’s lack of oxygen or increase in CO₂ levels were to blame for his high gamma activity. With such a small sample size, there is little way to work out whether the interpretation above is actually borne out by the data.

Techniques like EEG and magnetic resonance imaging (MRI) can prove powerful when they are given adequate data to play with. Vicente highlights innovative work into the content of dreams. Here, researchers used data taken from lucid dreamers capable of guiding their dreams. By looking at the brain activity produced when lucid dreamers thought of a particular scenario, they were eventually able to train a model to predict what a non-lucid dreamer was imagining in their own sleep. “It's not that you can recover the content perfectly,” says Vicente, “But I think accuracy is good enough as to claim that some very gross aspects of some subjective experiences, such as dreams, can be recovered to some degree.”

As our technology advances, perhaps techniques like MRI and EEG will be able to make more and more accurate predictions from smaller study sample sizes. But as a recent review of MRI research highlighted, many funded neuroimaging studies use sample sizes that are too small and underpowered. Vicente’s study is a reminder both of the human brain’s complexity and how limited we are in our ability to understand and decode it ‒ for now.

Reference: https://www.frontiersin.org/articles/10.3389/fnagi.2022.813531/full

Raul Vicente was speaking to Ruairi J Mackenzie, Senior Science Writer for Technology Networks