Category Archives: consciousness

Darwin’s Neuroscientist: Gerald M. Edelman, 1929-2014

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Dr. Gerald M. Edelman, 1929-2014.

“The brain is wider than the sky.
For, put them side by side,
The one the other will include,
With ease, and you beside.”

Dr. Gerald M. Edelman often used these lines from Emily Dickinson to introduce the deep mysteries of neuroscience and consciousness. Dr. Edelman (it was always ‘Dr.’), who has died in La Jolla, aged 84, was without doubt a scientific great. He was a Nobel laureate at the age of 43, a pioneer in immunology, embryology, molecular biology, and neuroscience, a shrewd political operator, and a Renaissance man of striking erudition who displayed a masterful knowledge of science, music, literature, and the visual arts who at one time could have been a concert violinist. He quoted Woody Allen and Jascha Heifetz as readily as Linus Pauling and Ludwig Wittgenstein, a compelling raconteur who loved telling a good Jewish joke just as much as explaining the principles of neuronal selection. And he was my mentor from the time I arrived as a freshly minted Ph.D. at The Neurosciences Institute in San Diego, back in 2001. His influence in biology and the neurosciences is inestimable. While his loss marks the end of an era, his legacy is sure to continue.

Gerald Maurice Edelman was born in Ozone Park, New York City, in 1929, to parents Edward and Anna. He trained in medicine at the University of Pennsylvania, graduating cum laude in 1954. After an internship at the Massachusetts General Hospital and three years in the US Army Medical Corp in France, Edelman entered the doctoral program at Rockefeller University, New York. Staying at Rockefeller after his Ph.D. he became Associate Dean and Vincent Astor Distinguished Professor, and in 1981 he founded The Neuroscience Institute (NSI). In 1992 the NSI moved lock, stock, and barrel into new purpose-built laboratories in La Jolla, California, where Edelman continued as Director for more than twenty years. A dedicated man, he continued working at the NSI until a week before he died.

In 1972 Edelman won the Nobel Prize in Physiology or Medicine (shared independently with Rodney Porter) for showing how antibodies can recognize an almost infinite range of invading antigens. Edelman’s insight, the principles of which resonate throughout his entire career, was based on variation and selection: antibodies undergo a process of ‘evolution within the body’ in order to match novel antigens. Crucially, he performed definitive experiments on the chemical structure of antibodies to support his idea [1].

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Dr. Edelman at Rockefeller University in 1972, explaining his model of gamma globulin.

Edelman then moved into embryology, discovering an important class of proteins known as ‘cell adhesion molecules’ [2]. Though this, too, was a major contribution, it was the biological basis of mind and consciousness – one of the ‘dark areas’ of science, where mystery reigned – that drew his attention for the rest of his long career. Over more than three decades Edelman developed his theory of neuronal group selection, also known as ‘neural Darwinism’, which again took principles of variation and selection, but here applied them to brain development and dynamics [3-7]. The theory is rich and still underappreciated. At its heart is the realization that the brain is very different from a computer: as he put it, brains don’t work with ‘logic and a clock’. Instead, Edelman emphasized the rampantly ‘re-entrant’ connectivity of the brain, with massively parallel bidirectional connections linking most brain regions. Uncovering the implications of re-entry remains a profound challenge today.

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The campus of The Neuroscience Institute in La Jolla, California.

Edelman was convinced that scientific breakthroughs require both sharp minds and inspiring environments. The NSI was founded as a monastery of science, supporting a small cadre of experimental and theoretical neuroscientists and enabling them to work on ambitious goals free from the immediate pressures of research funding and paper publication. This at least was the model, and Edelman struggled heroically to maintain its reality in the face of increasing financial pressures and the shifting landscape of academia. That he was able to succeed for so long attests to his political nous and focal determination as well as his intellectual prowess. I remember vividly the ritual lunches that exemplified life at the NSI. The entire scientific staff ate together at noon every day (except Fridays), at tables seemingly designed to hold just enough people so that the only common topic could be neuroscience; Edelman, of course, held court at one table, brainstorming and story-telling in equal measure. The NSI itself is a striking building, housing not only experimental laboratories but also a concert-grade auditorium. Science and art were, for Edelman, two manifestations of a fundamental urge towards creativity and beauty.

Edelman did not always take the easiest path through academic life. Among many rivalries, he enjoyed lively clashes with fellow Nobel laureate Francis Crick who, like Edelman himself, had turned his attention to the brain after resolving a central problem in a different area of biology. Crick once infamously referred to neural Darwinism as ‘neural Edelmanism’ [8], a criticism which nowadays seems less forceful as attention within neurosciences increasingly focuses on neuronal population dynamics (just before his death in 2004, Crick met with Edelman and they put aside any remaining feelings of enmity). In 2003 both men published influential papers setting out their respective ideas on consciousness [9, 10]; these papers put the neuroscience of consciousness at last, and for good, back on the agenda.

The biological basis of consciousness had been central to Edelman’s scientific agenda from the late 1980s. Consciousness had long been considered beyond the reach of science; Edelman was at the forefront its rehabilitation as a serious subject within biology. His approach was from the outset more subtle and sophisticated than those of his contemporaries. Rather than simply looking for ‘neural correlates of consciousness’ – brain areas or types of activity that happen to co-exist with conscious states – Edelman wanted to naturalize phenomenology itself. That is, he tried to establish formal mappings between phenomenological properties of conscious experience and homologous properties of neural dynamics. In short, this meant coming up with explanations rather than mere correlations, the idea being that such an approach would demystify the dualistic schism between ‘mind’ and ‘matter’ first invoked by Descartes. This approach was first outlined in his book The Remembered Present [5] and later amplified in A Universe of Consciousness, a work co-authored with Giulio Tononi [11]. It was this approach to consciousness that first drew me to the NSI and to Edelman, and I was not disappointed. These ideas, and the work they enabled, will continue to shape and define consciousness science for years to come.

My own memories of Edelman revolve entirely around life at the NSI. It was immediately obvious that he was not a distant boss who might leave his minions to get on with their research in isolation. He was generous with his time. I saw him almost every working day, and many discussions lasted long beyond their allotted duration. His dedication to detail sometimes took the breath away. On one occasion, while working on a paper together [12], I had fallen into the habit of giving him a hard copy of my latest effort each Friday evening. One Monday morning I noticed the appearance of a thick sheaf of papers on my desk. Over the weekend Edelman had cut and paste – with scissors and glue, not Microsoft Word – paragraphs, sentences, and individual words, to almost entirely rewrite my tentative text. Needless to say, it was much improved.

The abiding memory of anyone who has spent time with Dr. Edelman is however not the scientific accomplishments, not the achievements encompassed by the NSI, but instead the impression of an uncommon intellect moving more quickly and ranging more widely than seemed possible. The New York Times put it this way in a 2004 profile:

“Out of free-floating riffs, vaudevillian jokes, recollections, citations and patient explanations, out of the excited explosions of example and counterexample, associations develop, mental terrain is reordered, and ever grander patterns emerge.”

Dr. Edelman will long be remembered for his remarkably diverse scientific contributions, his strength of character, erudition, integrity, and humour, and for the warmth and dedication he showed to those fortunate enough to share his vision. He is survived by his wife, Maxine, and three children: David, Eric, and Judith.

Anil Seth
Professor of Cognitive and Computational Neuroscience
Co-Director, Sackler Centre for Consciousness Science
University of Sussex

This article has been republished in Frontiers in Conciousness Research doi: 10.3389/fpsyg.2014.00896

References

1 Edelman, G.M., Benacerraf, B., Ovary, Z., and Poulik, M.D. (1961) Structural differences among antibodies of different specificities. Proc Natl Acad Sci U S A 47, 1751-1758
2 Edelman, G.M. (1983) Cell adhesion molecules. Science 219, 450-457
3 Edelman, G.M. and Gally, J. (2001) Degeneracy and complexity in biological systems. Proc. Natl. Acad. Sci. USA 98, 13763-13768
4 Edelman, G.M. (1993) Neural Darwinism: selection and reentrant signaling in higher brain function. Neuron 10, 115-125.
5 Edelman, G.M. (1989) The remembered present. Basic Books
6 Edelman, G.M. (1987) Neural Darwinism: The Theory of Neuronal Group Selection. Basic Books, Inc.
7 Edelman, G.M. (1978) Group selection and phasic re-entrant signalling: a theory of higher brain function. In The Mindful Brain (Edelman, G.M. and Mountcastle, V.B., eds), MIT Press
8 Crick, F. (1989) Neural edelmanism. Trends Neurosci 12, 240-248
9 Edelman, G.M. (2003) Naturalizing consciousness: a theoretical framework. Proc Natl Acad Sci U S A 100, 5520-5524
10 Crick, F. and Koch, C. (2003) A framework for consciousness. Nature Neuroscience 6, 119-126
11 Edelman, G.M. and Tononi, G. (2000) A universe of consciousness : how matter becomes imagination. Basic Books
12 Seth, A.K., Izhikevich, E.I, Reeke, G.N, and Edelman, G.M. (2006) Theories and measures of consciousness: An extended framework. Proc Natl Acad Sci U S A 103, 10799-804

 

Accurate metacognition for visual sensory memory

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I’m co-author on a new paper in Psychological Science – a collaboration between the Sackler Centre (me and Adam Barrett) and the University of Amsterdam (where I am a Visiting Professor).  The new study addresses the continuing debate about whether the apparent rich content of our visual sensory scenes is somehow an illusion, as suggested by experiments like change blindness.  Here, we provide evidence in the opposite direction by showing that metacognition (literally, cognition about cognition) is equivalent for different kinds of visual memory, including visual ‘sensory’ memory which reflects brief, unattended, stimuli.  The results indicate that our subjective impression of seeing more than we can attend to is not an illusion, but is an accurate reflection of the richness of visual perception.

Accurate Metacognition for Visual Sensory Memory Representations.

The capacity to attend to multiple objects in the visual field is limited. However, introspectively, people feel that they see the whole visual world at once. Some scholars suggest that this introspective feeling is based on short-lived sensory memory representations, whereas others argue that the feeling of seeing more than can be attended to is illusory. Here, we investigated this phenomenon by combining objective memory performance with subjective confidence ratings during a change-detection task. This allowed us to compute a measure of metacognition-the degree of knowledge that subjects have about the correctness of their decisions-for different stages of memory. We show that subjects store more objects in sensory memory than they can attend to but, at the same time, have similar metacognition for sensory memory and working memory representations. This suggests that these subjective impressions are not an illusion but accurate reflections of the richness of visual perception.

The 30 Second Brain

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This week I’d like to highlight my new book, 30 Second Brain,  published by Icon Books on March 6th.  It is widely available in both the UK and the USA.  To whet your appetite here is a slightly amended version of the Introduction.

[New Scientist have just reviewed the book]

Understanding how the brain works is one of our greatest scientific quests.  The challenge is quite different from other frontiers in science.  Unlike the bizarre world of the very small in which quantum-mechanical particles can exist and not-exist at the same time, or the mind-boggling expanses of time and space conjured up in astronomy, the human brain is in one sense an everyday object: it is about the size and shape of a cauliflower, weighs about 1.5 kilograms, and has a texture like tofu.  It is the complexity of the brain that makes it so remarkable and difficult to fathom.  There are so many connections in the average adult human brain, that if you counted one each second, it would take you over 3 million years to finish.

Faced with such a daunting prospect it might seem as well to give up and do some gardening instead.  But the brain cannot be ignored.  As we live longer, more and more of us are suffering  – or will suffer – from neurodegenerative conditions like Alzheimer’s disease and dementia, and the incidence of psychiatric illnesses like depression and schizophrenia is also on the rise. Better treatments for these conditions depend on a better understanding of the brain’s intricate networks.

More fundamentally, the brain draws us in because the brain defines who we are.  It is much more than just a machine to think with. Hippocrates, the father of western medicine, recognized this long ago:  “Men ought to know that from nothing else but the brain come joys, delights, laughter and jests, and sorrows, griefs, despondency, and lamentations.” Much more recently Francis Crick – one of the major biologists of our time  – echoed the same idea: “You, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behaviour of a vast assembly of nerve cells and their associated molecules”.  And, perhaps less controversially but just as important, the brain is also responsible for the way we perceive the world and how we behave within it. So to understand the operation of the brain is to understand our own selves and our place in society and in nature, and by doing so to follow in the hallowed footsteps of giants like Copernicus and Darwin.

But how to begin?  From humble beginnings, neuroscience is now a vast enterprise involving scientists from many different disciplines and almost every country in the world.  The annual meeting of the ‘Society for Neuroscience’ attracts more than twenty thousand (and sometime more than thirty thousand!) brain scientists each year, all intent on talking about their own specific discoveries and finding out what’s new.  No single person – however capacious their brain – could possible keep track of such an enormous and fast-moving field.  Fortunately, as in any area of science, underlying all this complexity are some key ideas to help us get by.  Here’s where this book can help.

Within the pages of this book, leading neuroscientists will take you on a tour of fifty of the most exciting ideas in modern brain science, using simple plain English.  To start with, in ‘Building the brain’ we will learn about the basic components and design of the brain, and trace its history from birth (and before!), and over evolution.  ‘Brainy theories’ will introduce some of the most promising ideas about how the brain’s many billions of nerve cells (neurons) might work together.  The next chapter will show how new technologies are providing astonishing advances in our ability to map the brain and decipher its activity in time and space.  Then in ‘Consciousness’ we tackle the big question raised by Hippocrates and Crick, namely the still-mysterious relation between the brain and conscious experience – how does the buzzing of neurons transform into the subjective experience of being you, here, now, reading these words? Although the brain basis of consciousness happens to be my own particular research interest, much of the brain’s work is done below its radar – think of the delicate orchestration of muscles involved in picking up a cup, or in walking across the room.  So in the next chapter we will explore how the brain enables perception, action, cognition, and emotion, both with and without consciousness.  Finally, nothing – of course – ever stays the same. In the last chapter – ‘the changing brain –we will explore some very recent ideas about how the brain changes its structure and function throughout life, in both health and in disease.

Each of the 50 ideas is condensed into a concise, accessible and engaging ’30 second neuroscience’.  To get the main message across there is also a ‘3 second brainwave’, and a ‘3 minute brainstorm’ provides some extra food for thought on each topic. There are helpful glossaries summarizing the most important terms used in each chapter, as well as biographies of key scientists who helped make neuroscience what it is today.  Above all, I hope to convey that the science of the brain is just getting into its stride. These are exciting times and it’s time to put the old grey matter through its paces.

Update 29.04.14.  Foreign editions now arriving!

30SecBrainMontage

The limpid subtle peace of the ecstatic brain

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In Dostoevsky’s “The Idiot”, Prince Mychkine experiences repeated epileptic seizures accompanied by “an incredible hitherto unsuspected feeling of bliss and appeasement”, so that “All my problems, doubts and worries resolved themselves in a limpid subtle peace, with a feeling of understanding and awareness of the ‘Supreme Principal of life’”. Such ‘ecstatic epileptic seizures’ have been described many times since (usually with less lyricism), but only now is the brain basis of these supremely meaningful experiences becoming clear, thanks to remarkable new studies by Fabienne Picard and her colleagues at the University of Geneva.

Ecstatic seizures, besides being highly pleasurable, involve a constellation of other symptoms including an increased vividness of sensory perceptions, heightened feelings of self-awareness – of being “present” in the world – a feeling of time standing still, and an apparent clarity of mind where all things seem suddenly to make perfect sense. For some people this clarity involves a realization that a ‘higher power’ (or Supreme Principal) is responsible, though for atheists such beliefs usually recede once the seizure has passed.

In the brain, epilepsy is an electrical storm. Waves of synchronized electrical activity spread through the cortex, usually emanating from one or more specific regions where the local neural wiring may have gone awry.  While epilepsy can often be treated by medicines, in some instances surgery to remove the offending chunk of brain tissue is the only option. In these cases it is now becoming common to insert electrodes directly into the brains of surgical candidates, to better localize the ‘epileptic focus’ and to check that its removal would not cause severe impairments, like the loss of language or movement.  And herein lie some remarkable new opportunities.

Recently, Dr. Picard used just this method to record brain activity from a 23-year-old woman who has experienced ecstatic seizures since the age of 12. Picard found that her seizures involved electrical brain-storms centred on a particular region called the ‘anterior insula cortex’.  The key new finding was that electrical stimulation of this region, using the same electrodes, directly elicited ecstatic feelings – the first time this has been seen. These new data provide important support for previous brain-imaging studies which have shown increased blood flow to the anterior insula in other patients during similar episodes.

The anterior insula (named from the latin for ‘island’) is a particularly fascinating lump of brain tissue.  We have long known that it is involved in how we perceive the internal state of our body, and that these perceptions underlie emotional experiences. More recent evidence suggests that the subjective sensation of the passing of time depends on insular activity.  It also seems to be the place where perceptions of the outside world are integrated with perceptions of our body, perhaps supporting basic forms of self-consciousness and underpinning how we experience our relation to the world.  Strikingly, abnormal activity of the insula is associated with pathological anxiety (the opposite of ecstatic ‘certainty’) and symptoms of depersonalization and derealisation, where the self and world are drained of subjective reality (the opposite of ecstatic perceptual vividness and enhanced self-awareness). Anatomically the anterior insula is among the most highly developed brain regions in humans when compared to other animals, and it even houses a special kind of ‘Von Economo’ neuron. These and other findings are motivating new research, including experiments here at the Sackler Centre for Consciousness Science, which aim to further illuminate the role of the insula in the weaving the fabric of our experienced self. The finding that electrical stimulation of the insular can lead to ecstatic experiences and enhanced self-awareness provides an important advance in this direction.

Picard’s work brings renewed scientific attention to the richness of human experience, the positive as well as the negative, the spiritual as well as the mundane. The finding that ecstatic experiences can be induced by direct brain stimulation may seem both fascinating and troubling, but taking a scientific approach does not imply reducing these phenomena to the buzzing of neurons. Quite the opposite: our sense of wonder should be increased by perceiving connections between the peaks and troughs of our emotional lives and the intricate neural conversations on which they, at least partly, depend.

Interoceptive inference, emotion, and the embodied self

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ImageSince this is a new blog, forgive a bit of a catch up.  This is about a recent Trends Cognitive Sciences opinion article I wrote, applying the framework of predictive processing/coding to interoception, emotion, and the experience of body ownership.  There’s a lot of interest at the moment in understanding how interoception (the sense of the internal state of the body) and exteroception (everything else) interact.  Hopefully this will contribute in some way.  The full paper is here.

Interoceptive inference, emotion, and the embodied self

ABSTRACT:  The concept of the brain as a prediction machine has enjoyed a resurgence in the context of the Bayesian brain and predictive coding approaches within cognitive science. To date, this perspective has been applied primarily to exteroceptive perception (e.g., vision, audition), and action. Here, I describe a predictive, inferential perspective on interoception: ‘interoceptive inference’ conceives of subjective feeling states (emotions) as arising from actively-inferred generative (predictive) models of the causes of interoceptive afferents. The model generalizes ‘appraisal’ theories that view emotions as emerging from cognitive evaluations of physiological changes, and it sheds new light on the neurocognitive mechanisms that underlie the experience of body ownership and conscious selfhood in health and in neuropsychiatric illness.

As always, a pre-copy-edited version is here.

Predictive processing, sensorimotor theory, and perceptual presence

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I have a new ‘Discussion’ paper just out in the journal Cognitive Neuroscience. Right now there is just the target paper – eventually it will appear with published commentaries and my response.  The basic idea is to bring together, in a formal theoretical framework, ideas from Bayesian predictive processing and ‘enactive’ sensorimotor theory.  The new theory explains ‘perceptual presence’ in terms of the counterfactual richness of predictive representations, and it can also explain the absence of such presence in important cases like synaesthesia.

A predictive processing theory of sensorimotor contingencies: Explaining the puzzle of perceptual presence and its absence in synaesthesia

(A pre-copy-edit version can be obtained here)

ABSTRACT: Normal perception involves experiencing objects within perceptual scenes as real, as existing in the world. This property of “perceptual presence” has motivated “sensorimotor theories” which understand perception to involve the mastery of sensorimotor contingencies. However, the mechanistic basis of sensorimotor contingencies and their mastery has remained unclear. Sensorimotor theory also struggles to explain instances of perception, such as synaesthesia, that appear to lack perceptual presence and for which relevant sensorimotor contingencies are difficult to identify. On alternative “predictive processing” theories, perceptual content emerges from probabilistic inference on the external causes of sensory signals, however this view has addressed neither the problem of perceptual presence nor synaesthesia. Here, I describe a theory of predictive perception of sensorimotor contingencies which (i) accounts for perceptual presence in normal perception, as well as its absence in synaesthesia, and (ii) operationalizes the notion of sensorimotor contingencies and their mastery. The core idea is that generative models underlying perception incorporate explicitly counterfactual elements related to how sensory inputs would change on the basis of a broad repertoire of possible actions, even if those actions are not performed. These “counterfactually-rich” generative models encode sensorimotor contingencies related to repertoires of sensorimotor dependencies, with counterfactual richness determining the degree of perceptual presence associated with a stimulus. While the generative models underlying normal perception are typically counterfactually rich (reflecting a large repertoire of possible sensorimotor dependencies), those underlying synaesthetic concurrents are hypothesized to be counterfactually poor. In addition to accounting for the phenomenology of synaesthesia, the theory naturally accommodates phenomenological differences between a range of experiential states including dreaming, hallucination, and the like. It may also lead to a new view of the (in)determinacy of normal perception.

Near-death experiences: The brain’s last hurrah

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Brain scan MRI

We have all wondered what it will be like to die, and what – if anything – might happen afterwards. The prospect of no longer existing seems so difficult to accept that cultures throughout history have developed spiritual and religious beliefs about the persistence of consciousness after the body’s physical demise. Back in the 17th Century, Rene Descartes famously proposed that ‘mind stuff’ (res cogitans) has a separate form of existence from ‘material stuff’ (res extensa), thus introducing the thorny problem of how they might interact, and whether one might exist without the other.

Beliefs about persisting consciousness have been reinforced by reports of unusual ‘near death experiences’ which often involve the feeling that the soul has left the body and is approaching another reality characterized by bright light and blissful feelings. Now neuroscience has got in on the act, with a remarkable study by Jimo Borjigin and colleagues from the University of Michigan showing a transient surge in brain activity after the heart stops.

Most neuroscientists would be very sceptical of claims that consciousness of any sort could exist independently of a living brain. There is a growing consensus that consciousness, like life, weather, and cricket, is just another part of the natural world – albeit one that is reluctant to divulge its secrets. But it is unwise to dismiss reports of near-death experiences, which are usually reported after traumatic life-threatening events like heart attacks. What’s impressive is that these experiences are very consistent across individuals and even across cultures. I take this to mean that the people actually do have the experiences they say they have.

The challenge for science is to explain how the brain can generate these kinds of unusual experiences without assuming that consciousness can exist independently of the brain. Take the related phenomenon of ‘out of body experiences’, in which people experience themselves as being spatially separated from their body. The fact that people reliably report these events (sometimes as part of near-death experiences) does not mean their conscious self must literally leave their body to float around somewhere near the ceiling. We now know that similar experiences can be induced by electrically stimulating particular parts of the brain, or even by the clever use of virtual reality technology.

Some estimates suggest that up to 1 in 5 cardiac arrest survivors have near-death experiences, and given the traumatic contexts in which they occur it’s not surprising that they are sometimes interpreted as ‘proof’ of heaven or of some sort of afterlife. In reality, though, all aspects of these experiences can likely be explained just in terms of normal brain functions gone awry. Out-of-body experiences depend on the brain making the best guess of where its body is, based on sensory inputs. The so-called “tunnel of light” is not a stairway to heaven: it is probably caused by reduced blood flow to the retina and visual cortex (as occurs at high G-forces for test pilots). Abnormal activation of different brain regions, similar to what happens when dreaming, could account for re-experienced memories. Even strange phenomena like an awareness of being dead or seeing other apparently dead people can be related to similar delusions and hallucinations in other clinical conditions.

Despite all this, little has been known about what happens in the brain immediately after the heart stops beating. To address this, Borjigin’s team induced heart attacks in anesthetized rats and, surprisingly, found that brain activity continued after cardiac arrest, with some features actually becoming more prominent in the subsequent 30 seconds. Although these results are from rats and (fortunately) not people, they suggest the brain may have a final electrical ‘hurrah’ as it shuts down. If the same thing happens in humans, it might account for some other aspects of near-death experiences, like heightened alertness.

Looking ahead, the Michigan team’s work lays new foundations for a deeper scientific understanding of the unusual changes in the brain that accompany some of our more remarkable experiences. It also underlines that death is not an event but rather a process, something I became personally aware of while sitting with my father as he died earlier this year.

What is it like to die? We still don’t know, but now there is even less reason to invoke the paranormal, supernatural, or theological in shaping an explanation. And to me this only increases the wonder of life and of all the experiences it holds, even as it comes to an end.

Note:  This post first appeared in The Guardian on Aug 15, 2013.