Scientists Still Don’t Totally Understand What It Means to Be Conscious
Image: Xavier Aaronson/Motherboard

Scientists Still Don’t Totally Understand What It Means to Be Conscious

Axel Cleeremans, a psychologist and researcher, has spent the last 30 years trying to figure it out.

THE MOST UNKNOWN is Motherboard's love letter to the scientific process. For the next nine weeks, we'll be profiling the people trying to answer science's most difficult questions. Our feature-length documentary is now available on Netflix, and bonus episodes are available on YouTube.

Axel Cleeremans’s idea of a dream vacation is “when everybody thinks I’m on vacation, but I’m by myself working in my office.”


The man likes to work. But when your career is dedicated to unraveling one of life’s greatest mysteries, it can be hard to find anything else more fascinating than your day job. A PhD in cognitive psychology, Cleeremans is the director of the neuroscience institute at his alma mater, the Université Libre de Bruxelles, in Belgium, and runs a research group dedicated to answering one of humanity’s most elusive quandaries: why and how are we conscious?

It’s a question that requires equal expertise in neuroscience and philosophy—a marriage of disciplines that suits Cleeremans well. He tells me he’s often more interested in the questions that science elicits than by the answers it uncovers.

“It takes real skill to ask the correct questions, or to be able to say ‘that’s a good question’ or ‘that’s a bad question,’” Cleeremans told me during an interview via Skype.

How are we conscious, what is consciousness, and where does it live in the brain? These are some of the questions that Cleeremans has spent 30 years trying to answer.

To Find Out What It Is, Look at What It’s Not

I thought Cleeremans would laugh when I told him I wanted to start our interview with an “easy” question: what is consciousness? He gave me a polite chuckle, but then immediately slipped into a response. I guess I should have known that one of the world’s foremost consciousness researchers would have multiple definitions are the ready.


“The best definition is one that the philosopher Thomas Nagel came up with, which is ‘consciousness is what it feels like,’” Cleeremans said. “Whenever you’re present to the world, you have sensory contents—thoughts, mental objects—and that is what makes up consciousness.”

It’s a universal human experience that is, at once, deeply familiar and extremely elusive. It’s really difficult to describe what it feels like to be conscious, but we can all grasp what it is Cleeremans is studying. In particular, Cleeremans is interested in how the brain produces consciousness: what functions are happening in which parts of the brain that sparks this feeling of being alive and aware.

But how do you find consciousness in the brain? This is one of those questions Cleeremans loves.

“Coming up with good experiments is the biggest part of what approaching consciousness from a scientific perspective amounts to,” Cleeremans said.

Image: Xavier Aaronson/Motherboard

His strategy for designing experiments largely comes from something called the “contrastive approach:” the idea that we can understand consciousness by setting up scenarios where it is absent, and then comparing the two states. He records and observes the differences between the brain with a lack of consciousness and a brain with consciousness.

As an example, he describes an experiment with two situations. In the first, the person in the experiment is looking at a computer screen where an image flashes so quickly, they do not consciously perceive it. In the contrasting situation, all of the variables are the same, except this time the image flashes slowly enough for the person to perceive it consciously.


“You set up this contrast, trying to keep everything else equal except for the difference in consciousness,” Cleeremans said. “Now you can hunt for differences in brain activity between those two cases.”

Cleeremans focuses specifically on human consciousness, although the field expands to questions about all kinds of living species; Are dogs conscious? Is coral conscious? What about plants? But when we already understand so little about our most immediate, intimate realm of consciousness, the human mind, there’s more than enough for Cleeremans to spend a lifetime studying there without delving into these wider questions.

“Consciousness is this immediate data of your being alive as a human being and probably as many other animal species,” he said “It means something for you to be there, and that’s not the case for a table or a rock, even though some people would even defend that perspective.”

Cleeremans has spent three decades publishing dozens of findings that have helped expand our grasp of how consciousness functions in the brain, and where. He’s a prolific publisher (likely a product of someone who thinks working in peace is a form of vacation.) Take this 2016 paper, published in Current Biology. It describes how Cleeremans and his colleagues recreated a famous experiment from psychology: the Milgram trials, where subjects were willing to give an unseen stranger what they believed were painful, even deadly, electric shocks just because a person in a white coat told them to do it.


In Cleeremans’s approach, he didn’t just ask the participants why they behaved the way they did, he took electrophysiological recordings to measure the subjects’ sense of agency in the brain. By doing this, he was able to show that when someone is taking orders, their brain spends much less time considering the outcome of their actions. In other words: when taking orders, our sense of personal responsibility drops significantly.

“This demonstrates how even very low-level processes can be influenced by very high-level factors such as what we say and the social context in which interactions take place,” Cleeremans told me.

He was the first person to propose that a neural network could learn through implicit learning the way humans do. When you’re a baby, you’re learning all kinds of things even though you’re not actively trying to (babies don’t sit down at night studying their vowel sounds, it just comes naturally). He also helped to dismantle a long-held belief in how priming—subtle, unconscious stimulus—impacts subjects in studies.

Cleeremans walks D'Angelo through the experiment. Image: Motherboard

In Motherboard’s feature documentary, The Most Unknown, Cleeremans demonstrates some of the ways he applies these findings into new experiments. He hooks electrodes to visiting Italian physicist Davide D’Angelo’s and asks him to try to move a robotic hand using only his mind.

“What we’re trying to do here is learn what thoughts to imagine so that the hand will move,” Cleeremans says in the film. “The crucial argument is that this is not built in. During your development, your brain has to learn to interact with your body. Agency is part of what it means to be conscious.”


Thinking About Thinking

Growing up the son of an artist, Cleeremans said his home was filled with texts that expanded the mind: books of paintings, biology textbooks, microscope manuals. As a teenager, he built what he calls a “lab” in his bedroom where he would conduct at-home biology experiments.

When it came time to decide his college major, he was still interested in biology but had recently uncovered a love of philosophy as well.

“I didn’t really know what to do and so psychology felt like a compromise between those two things: biology and philosophy,” Cleeremans said, then corrected himself. “I mean, the truth is I got drunk with some friends who said they would study psychology so I said I would too. But it still sort of feels like a good compromise, and it turned out to be.”

In 1986, he graduated with a degree in psychology from Université Libre de Bruxelles, then moved stateside to complete a PhD at Carnegie Mellon University—an institution with a reputation for blending arts and science. His early research focused on neural networks and implicit learning, and at Carnegie Mellon he was imbued with a community of researchers on the cutting edge of artificial intelligence. He told me it was the beginning of a paradigm shift in psychology, where the study of A.I. raised new questions about how our natural intelligence works. At that time, consciousness started to become a hot topic in the field.


For Cleeremans, it was an easy transition from studying what we can do without awareness to start studying awareness itself. After attending the inaugural meeting of the Association for the Scientific Study of Consciousness in 1996—which Cleeremans calls a “watershed moment” in his career—it became clear that these were the questions he wanted to spend his career answering.

“What I did become more and more directed towards consciousness than towards what we can do without it,” Cleeremans said. “But as I said earlier, in order to look at consciousness you have to figure out what we can do without it. So in a way it’s very tightly connected with the first part of my career.”

Over time, he and others in the field have made great advancements. We know many of the physical spaces of the brain that contribute to consciousness, but it’s still not clear how these areas interact and if any single part of the brain is necessary for consciousness alone. Cleeremans’s main theory is based on the idea that the brain learns to be conscious, as he explained with the robot hand experiment. He posited it as a potential explanation for the case of a 44-year-old man whose brain, doctors discovered, was 90 percent fluid, yet still functioned normally. But even with all these achievements and discoveries, Cleeremans still doesn’t feel like he’s close to cracking the consciousness code.

Electrodes measure D'Angelo's brain activity. Image: Motherboard

“I’m 56 now, so I’ve spent 30 years thinking about these issues and it’s true sometimes you think, ‘is this going anywhere?’” Cleeremans said. “There is some frustration.”


He told me not just his specific work, but the field as a whole, can sometimes feel too big to capture, that this is a mystery that simply can’t be solved, at least not in his lifetime.

Towards the end of his segment on The Most Unknown, he confides in D’Angelo that this worry, that he won’t be able to capture the true scope of consciousness in his lifetime, keeps him awake at night.

“I wake up at night thinking about it, and there’s almost nothing else I think about,” Cleeremans says.

“So, you’re a nerd, too!” D’Angelo quips.

Cleeremans replies: “One hundred percent.”

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