What cats, cucumbers, and psychedelic drugs tell us about the nature of consciousness
About three years ago, cat owners around the world stumbled upon a strange phenomenon: their beloved pets appeared to be deathly afraid of cucumbers. This discovery quickly grew into an entire genre of viral video, and in case you aren’t familiar, a typical upload features a cat being scared witless—often stumbling backward wide-eyed or even springing into the air in panic—after finding a cucumber that its owner had covertly placed nearby.
It isn’t totally clear why this happens; it could be that cats mistake cucumbers for snakes, or it could stem from a more general fear of the unknown. Whatever the reason, cats tend to perceive cucumbers as a threat and react to them with dramatic flair.
If we look past the fact that deliberately scaring your pet is just plain cruel, cucumber-encumbered cats may actually have a good deal to tell us about how the human mind works. Like us, cats have brains that have been finely tuned throughout millions of years of evolution to make predictions and to behave with certainty in highly uncertain situations. When suddenly confronted with an unfamiliar object in a strange context, cats’ brains must quickly draw from prior experience and inborn dispositions to fill the gaps in their knowledge and act decisively. And to act decisively in this case often means, as sadistic cat owners have gleefully discovered, to treat cucumbers as a potential peril.
Many human behaviors are no different in essence; one may, for example, be frightened by sudden movement in a dark room because the brain, in the absence of sufficient evidence to the contrary, predicts that the movement could be a threat. The counterpart to this fear is that as we collect more information about the supposed threat—that is, as we attempt to correct the errors in our initial predictions—our fear tends to subside.
The brain’s capacity for prediction and error-correction is important for reasons that go far beyond knee-jerk threat responses. In fact, many neuroscientists believe that it is the main purpose of the brain, and that it forms the basis for our everyday experience of the world around us. As neuroscientist Anil Seth put it, “We don’t just passively perceive the world. We actively generate it.”
Consider the following example from writer Michael Pollan: “When you see a rectangle that’s about six-foot-six high and has this little dark thing right near the edge in the middle, you don’t have to perceive a door,” said Pollan during an interview on The Ezra Klein Show. “Your mind has got ‘door’ as one of its many, many pre-recorded ‘cassettes’ and it plugs that in.” Now, most of the time we don’t notice our brain’s reliance on predictive models of the outside world, or “cassettes,” as Pollan calls them. And that’s precisely the point. By whipping up models and plugging them in whenever possible, the brain streamlines perception and makes it much simpler to navigate everyday life.
To experience firsthand this principle in action—without having to stare intently at a door—have a close look at an optical illusion. Perceptual illusions of all kinds exploit flaws or biases in the brain’s predictions. They work by finding the mismatches between your brain’s “cassettes” and what’s actually out there in the world.
Prediction and error-correction are so integral to conscious perception that some neuroscientists have taken to calling consciousness a “controlled hallucination.” And it just so happens that all of us, because of our unique backgrounds, are “hallucinating” in unique ways. “Your consciousness is based on a set of models that are the product of your history—where you grew up, what the light was like, your size as an individual, and no doubt your age,” said Pollan. “So the models you are constantly projecting to understand your world might look different than mine.”
This idea sheds light on recent internet firestorms like the Yanny/Laurel and dress color debates: Which side we take depends largely on how our brains, loaded with all their unique and possibly flawed representations of the world, interpret ambiguous sensory information. And according to one recent study, the initial interpretation matters most; once we perceive ambiguity a certain way, we tend to lose the ability to perceive it any other way. “[These debates] are silly,” wrote Vox’s Brian Resnick. “But their lessons run deep: Our interpretations of reality are often arbitrary, but we’re stubborn about them nonetheless.” So that cucumber is a snake, that sudden movement is a monster, and, for the love of god, that dress is black and blue.
Pollan argues in his new book, How to Change Your Mind, that this rigidity in our mental frameworks, this interpretive stubbornness, applies not only to our experience of the external world, but also to the way we understand ourselves. The controlled hallucinations that make up our consciousness, it seems, project just as much inward as outward.
Evidence for this claim comes, oddly enough, from studies of actual hallucinations. When neuroscientist Robin Carhart-Harris and his team scanned the brains of people under the influence of psychedelic drugs like LSD and psilocybin, one of the most striking changes they observed was decreased activity in a structure known as the default mode network. This network, as Carhart-Harris told Scientific American, “seems to be the best candidate that we have for the biological underpinnings of the sense of self.” It’s involved in egocentric mental processes like self-reflection, contemplation of our past and future, and the construction of narratives about our lives that place us at center stage—all of which are habits that give us the impression, however questionable, that we are discrete entities, constant over time and separate from the world around us. And as hippies and empirical evidence alike tell us, those self-centered processes fade away in the presence of psychedelic drugs, a phenomenon called “ego dissolution.”
Now, an ego—that is, a strong, individualistic sense of self—can come in handy. It can, say, stoke ambition or help us defend ourselves. But Pollan argues that it can also be pathological. “[Mental illnesses like depression, anxiety, and addiction] involve uncontrollable and endlessly repeating loops of rumination that gradually shade out reality and fray our connections to other people and the natural world,” he wrote. “The ego becomes hyperactive, even tyrannical, enforcing rigid habits of thought and behavior.” Yet psychedelic drugs, he believes, could be one way to disrupt these harmful habits. By loosening the ego’s grip on mental function—or “lubricating cognition,” as Carhart-Harris puts it—they can help people become more aware of and even interrupt the unhealthy patterns that cause mental illness.
Their checkered past and the stigmas that come with it can make it difficult to talk about psychedelics in a grounded and productive way. But the data don’t lie. These drugs have considerable potential for treating depression, anxiety, PTSD, addiction, and even fear of death among cancer patients. Consider this excerpt from Pollan’s conversation with one of those cancer patients about her experience with psilocybin:
“I saw my fear…located under my ribcage,” a woman with ovarian cancer told me. “It wasn’t my tumor, it was this black mass. ‘Get the fuck out!’” she screamed aloud. “And you know what? It was gone!” Years later, her fear hasn’t returned. “The cancer is something completely out of my control, but the fear, I realized, is not.”
This woman’s experience points to what Pollan considers the most exciting part of the scientific study of psychedelics: that it may “yield a grand unified theory of mental illnesses” by allowing researchers to more thoroughly investigate subjective phenomena like fear, which have for years remained largely impenetrable to experimental inquiry. “There’s nothing more real to you than your subjective experience,” he said. “And there’s nothing more opaque to science—so far.”
The study of consciousness is overflowing with open questions. But if the latest research is any indication, we may soon enough trip and fall into some answers.