How to Change Your Mind

by Michael Pollan

  But the default mode network doesn’t only exert top-down control over material arising from within; it also helps regulate what is let into consciousness from the world outside. It operates as a kind of filter (or “reducing valve”) charged with admitting only that “measly trickle” of information required for us to get through the day. If not for the brain’s filtering mechanisms, the torrent of information the senses make available to our brains at any given moment might prove difficult to process—as indeed is sometimes the case during the psychedelic experience. “The question,” as David Nutt puts it, “is why the brain is ordinarily so constrained rather than so open?” The answer may be as simple as “efficiency.” Today most neuroscientists work under a paradigm of the brain as a prediction-making machine. To form a perception of something out in the world, the brain takes in as little sensory information as it needs to make an educated guess. We are forever cutting to the chase, basically, and leaping to conclusions, relying on prior experience to inform current perception.

  The mask experiment I attempted to perform during my psilocybin journey is a powerful demonstration of this phenomenon. At least when it is working normally, the brain, presented with a few visual clues suggesting it is looking at a face, insists on seeing the face as a convex structure even when it is not, because that’s the way faces usually are.

  The philosophical implications of “predictive coding” are deep and strange. The model suggests that our perceptions of the world offer us not a literal transcription of reality but rather a seamless illusion woven from both the data of our senses and the models in our memories. Normal waking consciousness feels perfectly transparent, and yet it is less a window on reality than the product of our imaginations—a kind of controlled hallucination. This raises a question: How is normal waking consciousness any different from other, seemingly less faithful productions of our imagination—such as dreams or psychotic delusions or psychedelic trips? In fact, all these states of consciousness are “imagined”: they’re mental constructs that weave together some news of the world with priors of various kinds. But in the case of normal waking consciousness, the handshake between the data of our senses and our preconceptions is especially firm. That’s because it is subject to a continual process of reality testing, as when you reach out to confirm the existence of the object in your visual field or, upon waking from a nightmare, consult your memory to see if you really did show up to teach a class without any clothes on. Unlike these other states of consciousness, ordinary waking consciousness has been optimized by natural selection to best facilitate our everyday survival.

  Indeed, that feeling of transparency we associate with ordinary consciousness may owe more to familiarity and habit than it does to verisimilitude. As a psychonaut acquaintance put it to me, “If it were possible to temporarily experience another person’s mental state, my guess is that it would feel more like a psychedelic state than a ‘normal’ state, because of its massive disparity with whatever mental state is habitual with you.”

  Another trippy thought experiment is to try to imagine the world as it appears to a creature with an entirely different sensory apparatus and way of life. You quickly realize there is no single reality out there waiting to be faithfully and comprehensively transcribed. Our senses have evolved for a much narrower purpose and take in only what serves our needs as animals of a particular kind. The bee perceives a substantially different spectrum of light than we do; to look at the world through its eyes is to perceive ultraviolet markings on the petals of flowers (evolved to guide their landings like runway lights) that don’t exist for us. That example is at least a kind of seeing—a sense we happen to share with bees. But how do we even begin to conceive of the sense that allows bees to register (through the hairs on their legs) the electromagnetic fields that plants produce? (A weak charge indicates another bee has recently visited the flower; depleted of nectar, it’s probably not worth a stop.) Then there is the world according to an octopus! Imagine how differently reality presents itself to a brain that has been so radically decentralized, its intelligence distributed across eight arms so that each of them can taste, touch, and even make its own “decisions” without consulting headquarters.

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  WHAT HAPPENS WHEN, under the influence of psychedelics, the usually firm handshake between brain and world breaks down? No one thing, as it turns out. I asked Carhart-Harris whether the tripping brain favors top-down predictions or bottom-up sensory data. “That’s the classic dilemma,” he suggested: whether the mind, unconstrained, will tend to favor its priors or the evidence of its senses. “You do often find a kind of impetuousness or overzealousness on the part of the priors, as when you see faces in the clouds.” Eager to make sense of the data rushing in, the brain leaps to erroneous conclusions and, sometimes, a hallucination results. (The paranoid does much the same thing, ferociously imposing a false narrative on the stream of incoming information.) But in other cases, the reducing valve opens wide to admit lots more information, unedited and sometimes welcome.

  People who are color-blind report being able to see certain colors for the first time when on psychedelics, and there is research to suggest that people hear music differently under the influence of these drugs. They process the timbre, or coloration, of music more acutely—a dimension of music that conveys emotion. When I listened to Bach’s cello suite during my psilocybin journey, I was certain I heard more of it than I ever had, registering shadings and nuances and tones that I hadn’t been able to hear before and haven’t heard since.

  Carhart-Harris thinks that psychedelics render the brain’s usual handshake of perception less stable and more slippery. The tripping brain may “slip back and forth” between imposing its priors and admitting the raw evidence of its senses. He suspects that there are moments during the psychedelic experience when confidence in our usual top-down concepts of reality collapses, opening the way for more bottom-up information to get through the filter. But when all that sensory information threatens to overwhelm us, the mind furiously generates new concepts (crazy or brilliant, it hardly matters) to make sense of it all—“and so you might see faces coming out of the rain.

  “That’s the brain doing what the brain does”—that is, working to reduce uncertainty by, in effect, telling itself stories.

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  THE HUMAN BRAIN is an inconceivably complex system—perhaps the most complex system ever to exist—in which an order has emerged, the highest expression of which is the sovereign self and our normal waking consciousness. By adulthood, the brain has gotten very good at observing and testing reality and developing reliable predictions about it that optimize our investments of energy (mental and otherwise) and therefore our chances of survival. Uncertainty is a complex brain’s biggest challenge, and predictive coding evolved to help us reduce it. In general, the kind of precooked or conventionalized thinking this adaptation produces serves us well. But only up to a point.

  Precisely where that point lies is a question Robin Carhart-Harris and his colleagues have explored in an ambitious and provocative paper titled “The Entropic Brain: A Theory of Conscious States Informed by Neuroimaging Research with Psychedelic Drugs,” published in Frontiers in Human Neuroscience in 2014. Here, Carhart-Harris attempts to lay out his grand synthesis of psychoanalysis and cognitive brain science. The question at its heart is, do we pay a price for the achievement of order and selfhood in the adult human mind? The paper concludes that we do. While suppressing entropy (in this context, a synonym for uncertainty) in the brain “serves to promote realism, foresight, careful reflection and an ability to recognize and overcome wishful and paranoid fantasies,” at the same time this achievement tends to “constrain cognition” and exert “a limiting or narrowing influence on consciousness.”

  After a series of Skype interviews, Robin Carhart-Harris and I were meeting for the first time, in his fifth-floor walk-up in an
unposh section of Notting Hill, a few months after the publication of the entropy paper. In person, I was struck by Robin’s youthfulness and intensity. For all his ambition, his affect is strikingly self-effacing and does little to prepare you for his willingness to venture out onto intellectual limbs that would scare off less intrepid scientists.

  The entropy paper asks us to conceive of the mind as an uncertainty-reducing machine with a few serious bugs in it. The sheer complexity of the human brain and the greater number of different mental states in its repertoire (as compared with other animals) make the maintenance of order a top priority, lest the system descend into chaos.

  Once upon a time, Carhart-Harris writes, the human or protohuman brain exhibited a much more anarchic form of “primary consciousness,” characterized by “magical thinking”—beliefs about the world that have been shaped by wishes and fears and supernatural interpretation. (In primary consciousness, Carhart-Harris writes, “cognition is less meticulous in its sampling of the external world and is instead easily biased by emotion, e.g., wishes and anxieties.”) Magical thinking is one way for human minds to reduce their uncertainty about the world, but it is less than optimal for the success of the species.

  A better way to suppress uncertainty and entropy in the human brain emerged with the evolution of the default mode network, Carhart-Harris contends, a brain-regulating system that is absent or undeveloped in lower animals and young children. Along with the default mode network, “a coherent sense of self or ‘ego’ emerges” and, with that, the human capacity for self-reflection and reason. Magical thinking gives way to “a more reality-bound style of thinking, governed by the ego.” Borrowing from Freud, he calls this more highly evolved mode of cognition “secondary consciousness.” Secondary consciousness “pays deference to reality and diligently seeks to represent the world as precisely as possible” in order to minimize “surprise and uncertainty (i.e. entropy).”

  The article offers an intriguing graphic depicting a “spectrum of cognitive states,” ranging from high-entropy mental states to low ones. At the high-entropy end of the spectrum, he lists psychedelic states; infant consciousness; early psychosis; magical thinking; and divergent or creative thinking. At the low-entropy end of the spectrum, he lists narrow or rigid thinking; addiction; obsessive-compulsive disorder; depression; anesthesia; and, finally, coma.

  Carhart-Harris suggests that the psychological “disorders” at the low-entropy end of the spectrum are not the result of a lack of order in the brain but rather stem from an excess of order. When the grooves of self-reflective thinking deepen and harden, the ego becomes overbearing. This is perhaps most clearly evident in depression, when the ego turns on itself and uncontrollable introspection gradually shades out reality. Carhart-Harris cites research indicating that this debilitating state of mind (sometimes called heavy self-consciousness or depressive realism) may be the result of a hyperactive default mode network, which can trap us in repetitive and destructive loops of rumination that eventually close us off from the world outside. Huxley’s reducing valve contracts to zero. Carhart-Harris believes that people suffering from a whole range of disorders characterized by excessively rigid patterns of thought—including addiction, obsessions, and eating disorders as well as depression—stand to benefit from “the ability of psychedelics to disrupt stereotyped patterns of thought and behavior by disintegrating the patterns of [neural] activity upon which they rest.”

  So it may be that some brains could stand to have a little more entropy, not less. This is where psychedelics come in. By quieting the default mode network, these compounds can loosen the ego’s grip on the machinery of the mind, “lubricating” cognition where before it had been rusted stuck. “Psychedelics alter consciousness by disorganizing brain activity,” Carhart-Harris writes. They increase the amount of entropy in the brain, with the result that the system reverts to a less constrained mode of cognition.*

  “It’s not just that one system drops away,” he says, “but that an older system reemerges.” That older system is primary consciousness, a mode of thinking in which the ego temporarily loses its dominion and the unconscious, now unregulated, “is brought into an observable space.” This, for Carhart-Harris, is the heuristic value of psychedelics to the study of the mind, though he sees therapeutic value as well.

  It’s worth noting that Carhart-Harris does not romanticize psychedelics and has little patience for the sort of “magical thinking” and “metaphysics” that they nourish in their acolytes—such as the idea that consciousness is “transpersonal,” a property of the universe rather than the human brain. In his view, the forms of consciousness that psychedelics unleash are regressions to a “more primitive” mode of cognition. With Freud, he believes that the loss of self, and the sense of oneness, characteristic of the mystical experience—whether occasioned by chemistry or religion—return us to the psychological condition of the infant on its mother’s breast, a stage when it has yet to develop a sense of itself as a separate and bounded individual. For Carhart-Harris, the pinnacle of human development is the achievement of this differentiated self, or ego, and its imposition of order on the anarchy of a primitive mind buffeted by fears and wishes and given to various forms of magical thinking. While he holds with Aldous Huxley that psychedelics throw open the doors of perception, he does not agree that everything that comes through that opening—including the “Mind at Large” that Huxley glimpsed—is necessarily real. “The psychedelic experience can yield a lot of fool’s gold,” he told me.

  Yet Carhart-Harris also believes there is genuine gold in the psychedelic experience. When we met, he offered examples of scientists whose own experiences with LSD had supplied them with insights into the workings of the brain. Too much entropy in the human brain may lead to atavistic thinking and, at the far end, madness, yet too little can cripple us as well. The grip of an overbearing ego can enforce a rigidity in our thinking that is psychologically destructive. It may be socially and politically destructive too, in that it closes the mind to information and alternative points of view.

  In one of our conversations, Robin speculated that a class of drugs with the power to overturn hierarchies in the mind and sponsor unconventional thinking has the potential to reshape users’ attitudes toward authority of all kinds; that is, the compounds may have a political effect. Many believe LSD played precisely that role in the political upheaval of the 1960s.

  “Was it that hippies gravitated to psychedelics, or do psychedelics create hippies? Nixon thought it was the latter. He may have been right!” Robin believes that psychedelics may also subtly shift people’s attitudes toward nature, which also underwent a sea change in the 1960s. When the influence of the DMN declines, so does our sense of separateness from our environment. His team at Imperial College has tested volunteers on a standard psychological scale that measures “nature relatedness” (respondents rate their agreement with statements like “I am not separate from nature, but a part of nature”). A psychedelic experience elevated people’s scores.*

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  SO WHAT DOES a high-entropy brain look like? The various scanning technologies that the Imperial College lab has used to map the tripping brain show that the specialized neural networks of the brain—such as the default mode network and the visual processing system—each become disintegrated, while the brain as a whole becomes more integrated as new connections spring up among regions that ordinarily kept mainly to themselves or were linked only via the central hub of the DMN. Put another way, the various networks of the brain became less specialized.

  “Distinct networks became less distinct under the drug,” Carhart-Harris and his colleagues wrote, “implying that they communicate more openly,” with other brain networks. “The brain operates with greater flexibility and interconnectedness under hallucinogens.”

  In a 2014 paper published in the Journal of the Royal Society Interface, the Imperial College team demon
strated how the usual lines of communications within the brain are radically reorganized when the default mode network goes off-line and the tide of entropy is allowed to rise. Using a scanning technique called magnetoencephalography, which maps electrical activity in the brain, the authors produced a map of the brain’s internal communications during normal waking consciousness and after an injection of psilocybin (shown on the following pages). In its normal state, shown on the left, the brain’s various networks (here depicted lining the circle, each represented by a different color) talk mostly to themselves, with a relatively few heavily trafficked pathways among them.

  But when the brain operates under the influence of psilocybin, as shown on the right, thousands of new connections form, linking far-flung brain regions that during normal waking consciousness don’t exchange much information. In effect, traffic is rerouted from a relatively small number of interstate highways onto myriad smaller roads linking a great many more destinations. The brain appears to become less specialized and more globally interconnected, with considerably more intercourse, or “cross talk,” among its various neighborhoods.

  There are several ways this temporary rewiring of the brain may affect mental experience. When the memory and emotion centers are allowed to communicate directly with the visual processing centers, it’s possible our wishes and fears, prejudices and emotions, begin to inform what we see—a hallmark of primary consciousness and a recipe for magical thinking. Likewise, the establishment of new linkages across brain systems can give rise to synesthesia, as when sense information gets cross-wired so that colors become sounds or sounds become tactile. Or the new links give rise to hallucination, as when the contents of my memory transformed my visual perception of Mary into María Sabina, or the image of my face in the mirror into a vision of my grandfather. The forming of still other kinds of novel connections could manifest in mental experience as a new idea, a fresh perspective, a creative insight, or the ascribing of new meanings to familiar things—or any number of the bizarre mental phenomena people on psychedelics report. The increase in entropy allows a thousand mental states to bloom, many of them bizarre and senseless, but some number of them revelatory, imaginative, and, at least potentially, transformative.