This episode is also on Bilibili too.
Hi everyone, how are you doing? I’m Zhichao Wei. In today’s episode, I’m going to walk you through The Brain and Consciousness, a popular-science classic by neuroscience heavyweight Stanislas Dehaene. The book explains in detail the brain mechanisms behind consciousness, and it also offers plenty of material for understanding consciousness from a psychological perspective. There’s a huge amount of good stuff in there, so I won’t try to cover everything today. Instead, I’m going to focus on the two most essential questions in the book: 1. What is consciousness for? 2. When consciousness arises, what exactly is happening in the brain?
These two questions happen to come from two different angles—psychology and neuroscience—but, amazingly, their answers are both tightly connected to the same keyword. That keyword is—information. I think that by the end of today’s discussion, you’ll have a very strong sense that consciousness is closely tied to the brain’s processing of information.
Before we get into those two questions, let me briefly introduce the author of The Brain and Consciousness. Stanislas Dehaene is a French neuroscientist, a T0-level scholar—a god among gods—and in 2014 he won The Brain Prize, known as the “Nobel Prize of neuroscience.” His research interests include, but aren’t limited to, the neural mechanisms behind language and mathematical abilities, the brain mechanisms of learning and education, and the neuroscience of consciousness. The breadth and depth of his work are honestly astonishing. For example, in The Brain and Consciousness, at least half of the groundbreaking studies he cites were, unbelievably, carried out by his own lab. That’s terrifyingly impressive. He’s also the originator of the famous “Global Neuronal Workspace” hypothesis in consciousness science, which we’ll get to later.
So now let’s enter the book and look at the first question: What is consciousness for? What does consciousness actually do to help us survive and reproduce?
In the book, Dehaene sums up four major functions of consciousness: compressing information, preserving information, transforming information, and sharing information.
The First Major Function of Consciousness: Compressing Information
Let’s start with the first function—and the most fundamental one of all—which is compressing information.
To make sense of this function, we need to compare consciousness with its opposite—unconsciousness. We know that many mental activities are things we can’t perceive or notice, yet they quietly influence our behavior. These are unconscious mental activities.
So how exactly do consciousness and unconsciousness divide up the work?
Here’s an analogy that should make it clear.
Imagine your brain as a country facing a severe terrorist threat. The country’s president now has to make a difficult decision: should he declare the nation to be in a state of war on terror?
And what does the president rely on to make that decision? Intelligence about the terrorist threat supplied by the intelligence agencies.
Under the president there’s an enormous intelligence service. Tens of thousands of agents are each showing off their own special skills, gathering counterterrorism intelligence through different channels. Some agents are undercover on the front lines, writing up what they learn inside enemy territory and sending reports to the intelligence agency’s database. Some are IT experts, cracking the passwords of terrorist organizations’ computers to obtain intelligence, then submitting what they know to the database. Others are interrogation specialists, questioning captured terrorists. They too record every detail of what they discover and upload it to the database.
These agents fighting on the front lines and diligently recording everything they see and hear are our unconsciousness. At every moment, the brain unconsciously collects and processes all kinds of information—some external information received through the eyes and ears, some sensations generated inside the body, and some vague thoughts beginning to form in the mind—just like those agents carrying out missions everywhere and gathering information.
All right, now President Brain opens the intelligence agency’s database, and an ocean of information comes crashing toward him. How does he decide? The intelligence he sees may well contradict itself. The undercover agent says a terrorist attack is definitely coming—they’re already mobilizing over here! The interrogation specialist says our questioning shows that the terrorists are actually bluffing; it’s all just for show.
So what should he do?
The president’s solution is extremely simple and blunt. Instead of reading the intelligence report by report, he aggregates everything and looks at the probability of each type of intelligence appearing. If more intelligence supports the possibility of a terrorist attack, outweighing the intelligence against it probabilistically, the president orders the country into a state of war on terror—and vice versa.
From the perspective of information processing, the information collected by the agents forms a probabilistic description of the various possibilities in the real world. It’s highly objective because it preserves enough detail to reflect the likelihood of different situations. But the problem is that it’s uncertain. It’s like the wave function describing an electron’s position in quantum mechanics: it’s a cloud of probabilities. It can’t tell you exactly where the electron is; it can only tell you the probability that the electron will appear at a given position.
And what does the president do? He’s like the macroscopic observer in quantum mechanics. Once a macroscopic observer observes the microscopic world, the electron’s wave function collapses. Macroscopic observation eliminates uncertainty and makes the electron settle into one single, definite position!
The president is our consciousness.
The president’s job is to simplify information. His task is to turn intelligence that contains all kinds of detail but remains uncertain into one simple, definite, unique judgment: will a terrorist attack happen, or will it not? Since his action can only be one thing—either order the country into a state of war or don’t—he has to simplify the information he receives into this kind of arbitrary, definite judgment before he can decide what to do.
In the same way, at any given moment, what our consciousness can experience is one single, definite interpretation of the objective world: either we see a flower, or we don’t.
Unconsciousness is probabilistic, but consciousness is all-or-nothing. Consciousness eliminates uncertainty; it removes ambiguity. To borrow the quantum-mechanics analogy from a moment ago, consciousness collapses the “wave function” of unconsciousness! But this isn’t a case of “when in doubt, invoke quantum mechanics.” It’s just an analogy. Don’t read too much into it—don’t read too much into it.
What I’ve just described has been verified by experimental data. Here’s roughly how scientists test it. Researchers superimpose a pattern moving to the left and a pattern moving to the right. The patterns are specially designed, of course. When people look at the superimposed image, they see either leftward motion or rightward motion. The researchers then adjust the ratio of the two images—for example, superimposing 70 left-moving images and 30 right-moving images—and show the result to participants many times, asking whether they see leftward or rightward motion.
The result is that participants have exactly a 70% chance of seeing leftward motion and a 30% chance of seeing rightward motion. The direction of motion they consciously perceive perfectly matches the ratio of the two types of images set by the researchers: 7:3. So it’s clear that the work of consciousness really is to simplify information represented by a probability distribution into one definite, unique judgment.
If you watched my video from last time about the science-fiction novel Blindsight, did anything occur to you? The spinning-dancer illusion I showed you last time is actually a case where the two possibilities—clockwise and counterclockwise rotation—are exactly 50% each. So, assuming you don’t have an innate preference for either direction, if you look at the image 100 times, you’ll see clockwise about 50 times and counterclockwise about 50 times.
In Blindsight, the science-fiction novel we discussed last time, the author argues that humans can see only one of the spinning dancer’s possibilities—clockwise or counterclockwise—because the human brain has limited information-processing capacity. But what I’ve just described gives us another way to understand it: the appearance of consciousness may sometimes be less about whether we’re capable enough and more about whether it is necessary. Information has to be simplified into one definite possibility so it can correspond to one definite action. What truly limits us may not be our ability to process information, but the fact that our actions have to involve trade-offs. We can’t “have it all.”
So consciousness may not be a bug in thinking, as that novel suggests. It may actually be a feature. The other three functions of consciousness will give us more chances to feel this for ourselves.
The Second Major Function of Consciousness: Preserving Information
Next, let’s look at the second major function of consciousness—preserving information.
Consciousness simplifies information for the reason we just discussed—to match a single, definite action—but there’s actually a second reason: only information that’s sufficiently distilled can remain continuously activated and be preserved in the brain for a period of time. Research shows that information recorded unconsciously is retained for an extremely short time. If a word flashes quickly on a screen—say, the character for “drink”—then even if you’re completely unaware that you saw it, your response to related words such as “water,” “alcohol,” and “milk tea” will speed up for a brief moment afterward. That’s an unconscious effect, but it lasts less than about one second. After one second, the impression left by the unconscious in your mind has almost completely vanished. Once information enters consciousness, however, it can be preserved in the mind for a considerably longer time. That is the second major function of consciousness: by preserving information over time, consciousness builds lasting thoughts.
Dehaene writes in the book: “Condensing the experience of the present moment and extending the time it remains in the brain is a characteristic of our conscious thought.”
In fact, we can not only keep current experiences going in our minds; through memory, we can also retrieve past experiences and knowledge into consciousness. We can bring future goals we want to accomplish into consciousness too, gather all this information together, analyze it, and make decisions. In other words, consciousness frees our thinking from “the present,” from the here and now, allowing it to roam freely along the timeline—remembering the past and predicting the future.
This function of consciousness is also supported by empirical data. Scientists repeatedly observe that whenever a task requires information to be held for a short period in order to complete it successfully, consciousness inevitably appears.
Preserving information: that’s the second major function of consciousness.
The Third Major Function of Consciousness: Transforming Information
Now let’s talk about the third major function of consciousness—transforming information.
Once information enters consciousness, it no longer decays with time, so the brain can carry out a series of transformations on it.
Try pausing this video right now and doing 12 times 13 in your head. Done? Didn’t you feel the calculation unfolding step by step, endlessly turning over in your mind? We can clearly become aware of the series of strategies we use when multiplying. For example, 12 squared is 144, and then we add another 12.
That kind of operation is consciousness’s privilege. The unconscious can’t work out what 12*13 is—unless you memorized the answer beforehand and can retrieve it directly from memory. Whenever a calculation involves processing information in several steps according to some rule, the unconscious is completely helpless.
From the perspective of information, consciousness can transform the information it receives at the start step by step, eventually outputting something entirely unrecognizable. That’s consciousness’s information-transformation function.
That’s the third function of consciousness—transforming information.
The fourth major function of consciousness: sharing information
Finally, we have the fourth major function of consciousness—sharing information. For human beings, the information recorded in consciousness doesn’t just circulate inside each person’s own head. Because language exists, consciousness can be transmitted between different brains. Dehaene says that in the course of human evolution, sharing information may have been one of consciousness’s core functions.
Of course, the richness of consciousness far exceeds language’s carrying capacity. What we perceive goes far beyond what we can describe. How many people have suffered because they couldn’t accurately express what they were feeling, right? But that may be precisely the third reason consciousness needs to simplify information: simplified information is easier to put into words, and therefore easier to share with other people. So sharing information with others was very likely a powerful driving force behind consciousness compressing information.
So it seems that the extraordinary development of human consciousness is also closely connected to the fact that we’re social animals. Our sophisticated consciousness may have gradually evolved over generations of ancestors chatting, swapping gossip, and trading tips on how to hunt.
Whole-brain ignition
All right, those are the four major functions of consciousness identified in The Brain and Consciousness: compressing information, storing information, transforming information, and sharing information. Every core function of consciousness involves processing information. As I understand it, consciousness is also a necessary condition for these information-processing operations. Whenever the brain is carrying out this kind of information processing, consciousness is bound to appear. So the aliens in the novel Blindsight we discussed last time—aliens that can get everything done using the unconscious alone—probably don’t exist.
Those were ways of understanding consciousness from a psychological perspective. Now let’s switch to neuroscience and look at what actually happens in the brain when consciousness appears.
In The Brain and Consciousness, Dehaene brings together findings from all kinds of research and discovers that when consciousness appears, there are four especially prominent signatures in the brain. The first three are highly technical, so I won’t unpack them here. We’ll focus on the crucial fourth signature.
This is the most characteristic difference between conscious and unconscious brain activity: unconscious brain activity is confined to a very narrow, local brain circuit, whereas conscious brain activity triggers “whole-brain ignition,” setting off a massive synchronous electrical signal that spans almost the entire cerebral cortex. It’s as if the unconscious is just one family in a village setting off fireworks, while consciousness is like the whole village setting off the same fireworks when the clock strikes midnight on New Year’s Eve.
Neuroscientists, including Dehaene, have observed in more than one experiment that when consciousness appears, extremely strong neural firing can first be detected in several regions on both sides of the prefrontal and parietal lobes. This high-frequency brain-wave oscillation appears roughly 300 milliseconds after the stimulus, which is the P3 wave familiar to anyone who does neuroscience research. If unconscious activity in these regions is like a few snowflakes drifting down on a mountain, the P3 wave triggered by consciousness is practically an avalanche. The brain activity produced by the unconscious and consciousness isn’t a difference of 49 versus 51; it’s more like 1 versus 10000. That’s the first obvious difference. More importantly, the brain activity triggered by consciousness is not only intense—it spreads across almost the entire cerebral cortex, producing a whole-brain synchronous oscillation.
Brain activity in one small region can spread rapidly throughout the brain because nerve cells—neurons—are a lot like octopuses, with extraordinarily long tentacles. Those tentacles are neuronal axons, and some can actually be several meters long. In the brain, neurons with long axons are especially concentrated in the prefrontal cortex. They can extend their axons to practically any corner of the brain; some axons even tangle together to form fiber bundles that you can barely see with the naked eye. Thanks to this network of interconnected long neuronal axons, local neural activity can very quickly influence other brain regions far away.
So why does the brain need to produce this whole-brain synchronous neural oscillation? Dehaene says it may be because whole-brain synchrony promotes the transmission of information.
Dehaene says: “In the vast neuronal forest of the cerebral cortex, millions of cells firing randomly can easily lose a small cluster of activated neurons. But if they all speak at once, their voices are much more likely to be heard and carried onward. Excited neurons often fire collectively and cooperatively in order to transmit important information. In essence, synchrony opens a channel for (information) exchange between distant neurons.”
See? Information again—always information! The most characteristic feature of consciousness, whole-brain synchronous oscillation, exists to transmit information efficiently.
The “Global Neuronal Workspace” hypothesis
Based on these findings, Dehaene went on to propose the very famous “Global Neuronal Workspace” hypothesis in the science of consciousness. The core idea is actually very simple—just one sentence: What is consciousness? Consciousness is the sharing of information across the whole brain.
Let me explain.
Our brains are actually made up of many functional modules, with different modules handling different problems: auditory processing, visual processing, language, memory, emotion, and so on. They’re a lot like programs on a computer: Photoshop handles images, Word handles documents, and PowerPoint makes presentations. When dealing with specialized problems, they each do their own thing and have basically no contact with one another. But if we have a goal that requires the abilities of several programs—for example, making a presentation introducing someone, which means editing a photo, writing copy, and putting everything into PowerPoint—we need to share some information among those programs. So we copy the person’s picture and part of the copy into the clipboard for all the programs to use.
Consciousness is basically this computer-like “clipboard.”
Consciousness is a workspace created by the brain, which is what “workspace” means in “Global Neuronal Workspace.” This workspace connects the brain’s various specialized processing modules, and the information that needs to be shared among them is placed in this workspace. Then, as needed, the information is dispatched to different functional modules in the brain for processing.
For example, I’m currently getting ready to buy a new car, and this decision-making process involves the coordinated work of multiple modules in my brain.
The visual-processing module analyzes the vehicle’s exterior design. The auditory-processing module may help evaluate the sound of the engine and the quality of the audio system. At the same time, the memory module supplies past driving experiences and knowledge of different models, while the emotional-processing module influences my subjective preferences.
In this decision-making process, all this information and all these processing results are gathered in the brain’s “Global Neuronal Workspace,” where they exchange information. Sensory information may sway preferences; information in memory may influence on-the-spot evaluation. Only this way can I weigh all kinds of factors together and make a final decision. This is what the “Global Neuronal Workspace” hypothesis describes: consciousness serves as a platform for integrating and coordinating different kinds of information, playing a central, hub-like role in decision-making.
All right, that brings us to the end. We’ve now covered the two most essential points in The Brain and Consciousness—the functions of consciousness and the neural signatures of consciousness. The brain’s compressing, storing, transforming, and sharing of information all depend on consciousness. And when consciousness appears, the brain produces a cross-regional synchronous oscillation, which may have something to do with different brain modules sharing information. The Brain and Consciousness is seriously hardcore science, with many ingeniously designed experiments showing how the researchers arrived at these conclusions. The book also includes some thought-provoking applied research, such as using these findings about the brain mechanisms of consciousness to investigate whether people in a vegetative state are conscious. But we’re out of time, so I’ll skip all that. If you’re interested, go pick up the book.
I’m Zhichao Wei. I’ll keep sharing, discussing, and interpreting all kinds of books with you on this channel. If you enjoy my episodes, please follow, like, save, and comment—it really matters to me. Thanks for your support, and I’ll see you next time.
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