How to Change Your Mind: What the New Science of Psychedelics Teaches Us About Consciousness, Dying, Addiction, Depression, and Transcendence

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.

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 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 imagination...

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 ...

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 cons...

“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.

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.

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.

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—“an...

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

The entropy paper asks us to conceive of the mind as an uncertainty-reducing machine with a few serious bugs in it.

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.

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 loop...

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.

In his view, the forms of consciousness that psychedelics unleash are regressions to a “more primitive” mode of cognition.

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.

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.

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.

“The brain operates with greater flexibility and interconnectedness under hallucinogens.”

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.

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.

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 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.

One way to think about this blooming of mental states is that it temporarily boosts the sheer amount of diversity in our mental life. If problem solving is anything like evolutionary adaptation, the more possibilities the mind has at its disposal, the more creative its solutions will

The finding by Roland Griffiths’s lab that the psychedelic experience leads to long-term changes in the personality trait of openness raises the possibility that some kind of learning takes place while the brain is rewired and that it might in some way persist.

THE IDEA that increasing the amount of entropy in the human brain might actually be good for us is surely counterintuitive.

Robin Carhart-Harris’s paper got me wondering if, at least for the mind, aging is really a process of declining entropy, the fading over time of what we should regard as a positive attribute of mental life.

Certainly by middle age, the sway of habitual thinking over the operations of the mind is nearly absolute. By now, I can count on past experience to propose quick and usually serviceable answers to just about any question reality poses, whether it’s about how to soothe a child or mollify a spouse, repair a sentence, accept a compliment, answer the next question, or make sense of whatever’s happening in the world.

With experience and time, it gets easier to cut to the chase and leap to conclusions—clichés that imply a kind of agility but that in fact may signify precis...

When, for example, I’m feeling especially generous or grateful, open to feelings and people and nature, I register a sense of expansion. This feeling is often accompanied by a diminution of ego, as well as a falloff in the attention paid to past and future on which the ego feasts.

By the same token, there is a pronounced sense of contraction when I’m obsessing about things or feeling fearful, defensive, rushed, worried, and regretful. (These last two feelings don’t exist without time travel.) At such times,

She cautions that our thinking about the subject is usually constrained by our own restricted experience of consciousness, which we naturally take to be the whole of it.

In The Philosophical Baby, Gopnik draws a useful distinction between the “spotlight consciousness” of adults and the “lantern consciousness” of young children. The first mode gives adults the ability to narrowly focus attention on a goal. (In his own remarks, Carhart-Harris called this “ego consciousness” or “consciousness with a point.”) In the second mode—lantern consciousness—attention is more widely diffused, allowing the child to take in information from virtually anywhere in her field of awareness, which is quite wide, wider than that of most adults. (By this measure, children are more conscious than adults, rather than less.)

To borrow Judson Brewer’s terms, lantern consciousness is expansive, spotlight consciousness narrow, or contracted.

Drawing on its wealth of experience, the adult mind performs low-temperature searches most of the time.

Gopnik believes that both the young child (five and under) and the adult on a psychedelic have a stronger predilection for the high-temperature search; in their quest to make sense of things, their minds explore not just the nearby and most likely but “the entire space of possibilities.”

High-temperature searches can yield answers that are more magical than realistic. Yet there are times when hot searches are the only way to solve a problem, and occasionally they return answers of surpassing beauty and originality. E=mc2 was the product of a high-temperature search.

“Children are better learners than adults in many cases when the solutions are nonobvious”

I think of childhood as the R&D stage of the species, concerned exclusively with learning and exploring. We adults are production and marketing.”

“The child’s brain is extremely plastic, good for learning, not accomplishing”—better for “exploring rather than exploiting.”