On a muggy June night in Greenwich Village, more than 800 neuroscientists, philosophers and curious people gathered in an auditorium. They came for the first results of an ambitious investigation into a profound question: what is consciousness?
To kick things off, two friends — David Chalmers, a philosopher, and Christof Koch, a neuroscientist — took the stage to recall an old bet. In June 1998, they had gone to a conference in Bremen, Germany, and ended up talking late one night at a local bar about the nature of consciousness.
Dr. Koch had worked for years with Francis Crick, a biologist who shared a Nobel Prize for uncovering the structure of DNA, in search of what they called the “neural correlate of consciousness.” They believed that every conscious experience we have – staring at a painting, for example – is related to the activity of certain neurons essential to the consciousness associated with it.
Dr. Chalmers liked the concept, but he was skeptical that they would be able to find such a neural marker anytime soon. Scientists had far too much to learn about consciousness and the brain, he thought, before they could have any reasonable hope of finding it.
Dr. Koch bet his friend that scientists would find a neural correlate of consciousness within 25 years. Dr. Chalmers took the bet. The prize would be a few bottles of good wine.
Dr. Koch recalled the bet from the auditorium stage and admitted it was fueled by drinks and enthusiasm. “When you’re young, you have to believe that things will be simple,” he said.
Much has happened in the ensuing quarter of a century. Neuroscientists and engineers invented powerful new tools to probe the brain, leading to a burst of revealing experiments on consciousness. For example, some scientists have used brain scans to detect signs of consciousness in people diagnosed in a vegetative state, while others have used brain waves to determine when people become unconscious under anesthesia.
Those experiments led to an explosion of new theories. To winnow them, the Templeton World Charity Foundation has begun supporting large-scale studies in which different pairs of theories are directly tested, in a process called adversarial cooperation.
And last month at the New York event, researchers unveiled the results of the foundation’s first trial, combining two of its most prominent theories.
The first, known as the Global Workspace Theory, states that consciousness is a by-product of the way we process information. Neuroscientists have long known that most of the signals that come from our senses never reach our consciousness. Experiments led by Stanislas Dehaene, a cognitive neuroscientist at the Collège de France in Paris, suggest that we only become aware of signals that reach the prefrontal cortex, an area at the front of the brain. Dr. Dehaene has argued that a special set of neurons there can quickly relay the information through much of the brain, generating consciousness.
“Consciousness is the global availability of information,” said Dr. Dehaene.
Dr. Melanie Boly, a neurologist at the University of Wisconsin, took the stage to explain the other participant: Integrated Information Theory.
What makes consciousness special, Dr. Boly argued, is the way it manages to feel simultaneously rich and unified over time. Brains can produce such a phenomenon thanks to the way neurons are arranged, she said. Clusters of them can process information in certain ways, such as identifying the colors or contours in an image. But long-distance connections between those clusters also allow them to transfer information.
In 2017, Dr. Koch, then at the Allen Institute in Seattle, assigned a dozen experts to the institute to develop experiments that would test the two theories against each other. Dr. Chalmers also came from New York University to provide philosophical rigor. They agreed in advance what the results of each experiment would mean for each theory. And the experiments would be conducted by independent scientists who had pushed neither theory.
Brian Nosek, a psychologist at the University of Virginia who was not involved in the new study, praised the scientists for working together in such an ambitious experiment. “It’s hard because researchers are invested in their ideas,” he said. “Pre-commitment requires intellectual humility and a willingness to find out we’re wrong.”
The Cogitate Consortium, as the team called itself, took two years to prepare the experiment, but was beleaguered by the coronavirus pandemic. In May 2022, the researchers could start collecting data.
They asked 256 volunteers to look at a series of faces, letters and shapes and then press a button under certain circumstances, such as if the photo was a face or a certain person’s face.
Some volunteers performed the tasks in an fMRI brain scanner, which measures the flow of oxygenated blood in the brain. Others were observed with magnetoencephalography, which reads magnetic fields in the brain. The researchers also found volunteers preparing for brain surgery for epilepsy. They underwent the tests with implants inserted directly into their brains.
The researchers looked for common brain patterns that emerged when the volunteers had the conscious experience of seeing an object — regardless of what they saw, what their task was, or what technology was recording their activity.
The two theories made different predictions about what patterns the scientists would see. According to the Global Workspace Theory, the clearest signal would come from the prefrontal cortex, as it transmits information throughout the brain. The Integrated Information Theory, on the other hand, predicted that regions with the most complex connections – those in the back of the brain – would be the most active.
The timing of the activity may also point to one theory or the other. The Global Workspace Theory predicted that the prefrontal cortex would only send out short bursts of information — one when a picture first appeared and one when it disappeared. But Integrated Information Theory predicted that the back of the brain would be continuously active during the time volunteers were perceiving an object.
Lucia Melloni, a neuroscientist at the Max Planck Institute for Empirical Aesthetics in Germany who helped lead the experiments, took the stage to present the results with images of brains splashed in red, blue and green projected onto a giant screen.
Dr. Melloni explained that in some tests there was a clear winner and a clear loser. For example, activity in the back of the brain lasted the entire time volunteers saw an object. Score one for Integrated Information Theory. But in other tests, the predictions of the Global Workspace Theory came true.
After reviewing the mixed results, Dr. Dehaene and Dr. Boly joins Dr. Melloni to discuss them. Neither champion was willing to give in.
“I am very happy with it,” said Dr. Dehaene.
Dr. Boly concluded: “Overall, our impression is that the results confirm IIT’s predictions”
When the moderator, Heather Berlin of the Icahn School of Medicine at Mount Sinai in New York, Dr. Melloni asked what she thought, she chose her words carefully.
“My thought is that I come from a family of divorced parents,” she said. “And you love them both.”
Dr. Melloni and her colleagues posted the results online and submitted them to a scientific journal.
The Cogitate Consortium is conducting other experiments, including a video game in which objects move across a screen and flash on and off. The results of those richer experiences can move the evidence toward one theory.
“The current experiment is enough to show that neither theory is currently adequate,” said Anil Seth, a neuroscientist at the University of Sussex in England.
But at least the 25-year bet is settled: no one has found a clear neural correlate of consciousness. Dr. Koch ended the evening by carrying a wooden box full of wine to the stage. He pulled out a bottle of 1978 Madeira and handed it to Dr. Chalmers.
He then challenged his friend to another bet, this time double or nothing: a brain marker of consciousness by 2048.
Dr. Chalmers immediately shook up the bet, despite the dubious chance that either will be alive to see the outcome.
“I hope I lose,” he said. “But I suspect I’m going to win.”