Philosophers, psychologists, neuroscientists, plant biologists and novelists have all grappled with the mysteries of conscious experience, to an uncertain end.
If you have access to Nature, you can also read this review by Christoph Koch on its website.
Humans and other animals have subjective inner mental lives, seeing, smelling, imagining, remembering and feeling emotions such as anger and boredom. These experiences are innate but remain utterly unpredictable on the basis of the physical sciences — nothing explains how living matter can love or hate, daydream about sex, or fear for the future.
As journalist Michael Pollan recounts in A World Appears, the use of a handful of organic compounds can demonstrate that these sensations are constructs shaped and formed by the brain — and that these sensations can be expanded considerably. “In small doses, psychedelics smudge the pane of normal perception,” he notes. “The experience defamiliarizes everyday consciousness, allowing us to see it freshly.”What is the future of intelligence? The answer could lie in the story of its evolution
The author’s own experiences with psychedelics were what initiated his exploration of consciousness. A World Appears is a beautifully crafted, personal account of his five-year-long quest to understand how scientists, philosophers and novelists explore the nature of conscious experience.
The modern era of consciousness research began in the early 1990s. Researchers sought to tackle what philosopher David Chalmers called the ‘hard problem’ of consciousness: the challenge of explaining why any physical process — be it neurons firing at particular frequencies or the transmission of information through specific regions of the brain — should ‘feel’ like anything at all.
Researchers began trying to identify the brain circuits and cells that lead to the experience of consciousness in mammals. They focused on the neocortex, the brain’s outermost layer, which is often assumed to be responsible for consciousness.
Although this lofty goal of identifying brain circuits is yet to be achieved, in parallel, scientists have developed formal, empirically testable theories that relate consciousness to underlying neural circuits. Pollan focuses on two of them: integrated information theory and global neuronal workspace theory. I have skin in the game, having long backed one of these theories, so I will refrain from saying anything more except that they remain disputed and that Pollan interviewed me several times for this book. But Pollan’s heart isn’t in theories — he prefers the buzz of lived qualitative experience to the bloodless abstract quantities needed to construct mathematical models.
Staying stable
A World Appears starts with the topic of sentience — effectively the feeling of being alive, or proto-consciousness. Pollan, a lifelong gardener and plant lover, interviews philosopher Paco Calvo and two plant biologists, Stefan Mancuso and František Baluška. They argue that plants are sentient, can be anaesthetized and can solve problems — and that they must therefore be considered intelligent. Perhaps, Pollan muses, neurons are not needed for sentience. Their importance might be overestimated because of how crucial the brain is for humans.How does the brain control consciousness? This deep-brain structure
Pollan also talks to Karl Friston, the architect of the ‘free energy’ principle. This idea suggests that all organisms are constantly monitoring their internal and external environment for deviations from their ‘set points’, like glorified thermostats. Bacteria, plants and animals all try to infer the hidden causes of their sensory inputs to better predict what is likely to happen in the future. Consciousness, according to this theory, is “felt uncertainty”.
Inspired by many such conversations (and the consumption of magic mushrooms), Pollan comes away with the conviction that all creatures are endowed with some measure of sentience. Perhaps life and consciousness are intimately intertwined. This would force a considerable revision of the contemporary, brain-centric view of consciousness.
The next stop in Pollan’s investigation is emotion — feelings that are ‘embodied’, or rooted in bodily sensations. Emotions come with positive and negative associations, such as feeling pain or pleasure, cold or hot, and hungry or full. He speaks to neuroscientist Antonio Damasio and psychoanalyst Mark Solms, who introduce him to the idea that the source of these feelings is the upper brainstem. This brain region evolved early in evolutionary history, implying that consciousness does not depend on the neocortex, which evolved later. Both researchers, like Friston, link consciousness to an organism’s need for a stable internal environment and the ability to adapt to ever-changing circumstances — information that is relayed through the brainstem’s interoceptive neurons, which process signals from the whole body.
Robots or self-driving cars likewise need to monitor their internal and external environments and react to deviations from the norm. Accordingly, Damasio and, independently, Solms are trying to engineer a conscious artificial-intelligence agent by giving it preferences (to keep operating temperatures consistent) and simple goals (to reduce uncertainty by building a model of its environment), and eventually plan to embed it into a robot.
This embodied approach stands in marked contrast to the disembodied neural networks that power current cutting-edge AI programs, such as large language models, which some researchers suggest are on the threshold of becoming conscious. Yet, without a generally accepted theory of consciousness — and given humanity’s propensity to attribute agency to inanimate objects — how would we know? As Pollan trenchantly remarks, asking the model itself “won’t work when the AI has been trained on pretty much everything that’s been said and written about consciousness”. He challenges researchers to remove all reference to consciousness from the data set on which an AI program is trained to see if it can still discuss consciousness convincingly.
Pollan is sceptical of the idea that “there are no obvious barriers to building conscious AI systems”. To him, too many emotions — such as fear, desire and disgust — are anchored in bodily sensations to be credibly reproduced by computer software.AI models were given four weeks of therapy: the results worried researchers
Next, the author explores thought — “the actual contents of our consciousness”. As he complains, the dominant theories of consciousness have little to say about the fragmentary images, words, flashes of memories, ruminations and other flotsam that make up our stream of consciousness. He dives into the work of nineteenth-century psychologist William James, who grappled with the impossibility of studying thoughts in an impartial manner, given that the act of studying is itself a conscious process. It’s harder than one might think, Pollan realizes, to answer the question “What am I thinking?”.
He takes part in an experiment using the descriptive experience sampling strategy proposed by psychologist Russell Hurlburt. This method involves wearing an earpiece for several days that beeps at random times. When it goes off, Pollan has to write down, with as much precision as he can muster, the content of his mental experience at that precise moment. In lengthy follow-up interviews, Hurlburt tries to extract Pollan’s inner experience from these entries. Yet Pollan finds that isolating a single moment of thought proves to be elusive and unsatisfactory, like grasping at a ripple on the surface of a stream.
Pollan interviews novelist Lucy Ellmann, whose stream-of-consciousness-style book Ducks, Newburyport (2019) spans some 1,000 pages. The book unfolds in a single sentence, capturing the inner experiences of an ordinary woman and mother as she lives her life, even when they are full of non sequiturs, random snippets of observations, thoughts and memories. Pollan conveys the frustration of examining one’s own experience effectively — a self-referential loop similar to the ouroboros, a serpent eating its own tail. He concludes that, frustratingly, introspection is the closest we can get to the perception of thinking.
Impulse control
Finally, Pollan arrives at the most refined form of adult human consciousness — the self. This is the ‘I’ that perceives, thinks, experiences, knows and acts. It is the carrier of the behavioural traits and memories that make me, me, and you, you. The self is impossible to pin down and is deemed illusory in many religious and philosophical traditions.
He speaks to developmental psychologist Alison Gopnik who argues that young children have ‘lantern consciousness’ — a panoramic view of the world that allows them to take in “information and sensation from all around them all the time”. As we develop, this slowly turns into ‘spotlight consciousness’, which enables teenagers and adults to focus for a protracted amount of time on a singular task, be it a computer game or homework. This transition goes hand in hand with the emergence of the ‘self’ — the process of attaining self-discipline and becoming self-confident. Possessing a sense of self enables us to get ready in the morning, write book reviews and save for a distant retirement, none of which a young child can do independently.Great power and great responsibility: how consciousness changes the world
The self can also be dysfunctional. Narcissism, an over-inflated sense of self, is evident in many authoritarian leaders. The opposite, an underdeveloped sense of self, leads to self-belittlement, low self-esteem and chronic shame.
Remarkably, the sense of self can be lost (and found again) spontaneously, during religious, meditative or near-death experiences — or when using psychedelics. While tripping, Pollan perceives himself dissolving into a cloud of blue Post-it notes. His ability to distinguish between his self and the world fades and his individual consciousness seems to merge with a universal mind. Thomas Metzinger, a philosopher and author of Being No One (2004), refers to such mystical experiences as ‘pure awareness’. Many individuals throughout the ages who have encountered mystical experiences consider them to be one of the most meaningful experiences of their lives, conveying an overwhelming sense of having accessed what the writer Aldous Huxley, in The Doors of Perception (1954), called mind at large.
After arduously seeking an understanding of the relationship between the mind and the body, Pollan arrives at a Socratic ‘I know that I don’t know’ conclusion. His quest ends at a silent retreat in the Sangre de Cristo mountains in Colorado — appreciating the miracle of being conscious.
Having dedicated much of my professional life to the pursuit of consciousness and its basis in the brain, I am witness to empirical progress in the field. Yet, I loved this literary account of Pollan’s inconclusive yet insightful journey of discovery. And I am sympathetic to his attitude. The mind remains unfathomable — at least this side of death.
Nature 650, 546-548 (2026)
doi: https://doi.org/10.1038/d41586-026-00448-5
Competing Interests
C.K. has a financial interest, and holds an executive position, at Intrinsic Powers, Inc., a company whose purpose is to develop a device to assess the presence of consciousness in behaviorally unresponsive patients.