This transcript has been edited for clarity.
Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I’m Dr F. Perry Wilson of the Yale School of Medicine.
All the participants in the study I am going to tell you about this week died. And three of them died twice. But their deaths provide us with a fascinating window into the complex electrochemistry of the dying brain. What we might be looking at, indeed, is the physiologic correlate of the near-death experience.
The concept of the near-death experience is culturally ubiquitous. And though the content seems to track along culture lines – Western Christians are more likely to report seeing guardian angels, while Hindus are more likely to report seeing messengers of the god of death – certain factors seem to transcend culture: an out-of-body experience; a feeling of peace; and, of course, the light at the end of the tunnel.
As a materialist, I won’t discuss the possibility that these commonalities reflect some metaphysical structure to the afterlife. More likely, it seems to me, is that the commonalities result from the fact that the experience is mediated by our brains, and our brains, when dying, may be more alike than different.
We are talking about this study, appearing in the Proceedings of the National Academy of Sciences, by Jimo Borjigin and her team.
Dr. Borjigin studies the neural correlates of consciousness, perhaps one of the biggest questions in all of science today. To wit,
The study in question follows four unconscious patients –comatose patients, really – as life-sustaining support was withdrawn, up until the moment of death. Three had suffered severe anoxic brain injury in the setting of prolonged cardiac arrest. Though the heart was restarted, the brain damage was severe. The fourth had a large brain hemorrhage. All four patients were thus comatose and, though not brain-dead, unresponsive – with the lowest possible Glasgow Coma Scale score. No response to outside stimuli.
The families had made the decision to withdraw life support – to remove the breathing tube – but agreed to enroll their loved one in the study.
The team applied EEG leads to the head, EKG leads to the chest, and other monitoring equipment to observe the physiologic changes that occurred as the comatose and unresponsive patient died.
As the heart rhythm evolved from this:
PNAS
To this:
PNAS
And eventually stopped.
But this is a study about the brain, not the heart.
Prior to the withdrawal of life support, the brain electrical signals looked like this:
PNAS/F. Perry Wilson, MD, MSCE
What you see is the EEG power at various frequencies, with red being higher. All the red was down at the low frequencies. Consciousness, at least as we understand it, is a higher-frequency phenomenon.
Right after the breathing tube was removed, the power didn’t change too much, but you can see some increased activity at the higher frequencies.
PNAS/F. Perry Wilson, MD, MSCE
But in two of the four patients, something really surprising happened. Watch what happens as the brain gets closer and closer to death.
PNAS/F. Perry Wilson, MD, MSCE
Here, about 300 seconds before death, there was a power surge at the high gamma frequencies.
PNAS/F. Perry Wilson, MD, MSCE
This spike in power occurred in the somatosensory cortex and the dorsolateral prefrontal cortex, areas that are associated with conscious experience. It seems that this patient, 5 minutes before death, was experiencing something.
But I know what you’re thinking. This is a brain that is not receiving oxygen. Cells are going to become disordered quickly and start firing randomly – a last gasp, so to speak, before the end. Meaningless noise.
But connectivity mapping tells a different story. The signals seem to have structure.
Those high-frequency power surges increased connectivity in the posterior cortical “hot zone,” an area of the brain many researchers feel is necessary for conscious perception. This figure is not a map of raw brain electrical output like the one I showed before, but of coherence between brain regions in the consciousness hot zone. Those red areas indicate cross-talk – not the disordered scream of dying neurons, but a last set of messages passing back and forth from the parietal and posterior temporal lobes.
PNAS
In fact, the electrical patterns of the brains in these patients looked very similar to the patterns seen in dreaming humans, as well as in patients with epilepsy who report sensations of out-of-body experiences.
It’s critical to realize two things here. First, these signals of consciousness were not present before life support was withdrawn. These comatose patients had minimal brain activity; there was no evidence that they were experiencing anything before the process of dying began. These brains are behaving fundamentally differently near death.
But second, we must realize that, although the brains of these individuals, in their last moments, appeared to be acting in a way that conscious brains act, we have no way of knowing if the patients were truly having a conscious experience. As I said, all the patients in the study died. Short of those metaphysics I alluded to earlier, we will have no way to ask them how they experienced their final moments.
Let’s be clear: This study doesn’t answer the question of what happens when we die. It says nothing about life after death or the existence or persistence of the soul. But what it does do is shed light on an incredibly difficult problem in neuroscience: the problem of consciousness. And as studies like this move forward, we may discover that the root of consciousness comes not from the breath of God or the energy of a living universe, but from very specific parts of the very complicated machine that is the brain, acting together to produce something transcendent. And to me, that is no less sublime.
Dr. Wilson is an associate professor of medicine and director of Yale’s Clinical and Translational Research Accelerator, Yale University, New Haven, Conn. His science communication work can be found in the Huffington Post, on NPR, and on Medscape. He tweets @fperrywilson and his new book, How Medicine Works and When It Doesn’t, is available now. Dr. Wilson has disclosed no relevant financial relationships.