Two leading theories of consciousness square off
For years, Dr. Koch had collaborated with Francis Crick, a biologist who shared a Nobel Prize for uncovering the structure of DNA, on a quest for what they called the “neural correlate of consciousness.”
On a muggy June night in Greenwich Village, more than 800 neuroscientists, philosophers and curious members of the public packed into 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.
For years, Dr. Koch had collaborated with Francis Crick, a biologist who shared a Nobel Prize for uncovering the structure of DNA, on a quest for what they called the “neural correlate of consciousness.” They believed that every conscious experience we have — gazing at a painting, for example — is associated with the activity of certain neurons essential for the awareness that comes with it. Dr. Chalmers liked the concept, but he was skeptical that they could find such a neural marker any time soon. Scientists still had too much to learn about consciousness and the brain, he figured, before they could have a reasonable hope of finding it.
Dr. Koch wagered 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 fine wine. Recalling the bet from the auditorium stage, Dr. Koch admitted that it had been fuelled by drinks and enthusiasm. “When you’re young, you’ve got to believe things will be simple,” he said. A lot has happened over the subsequent quarter century.
Neuroscientists and engineers invented powerful new tools for probing the brain, leading to a burst of revealing experiments about consciousness. Some scientists have used brain scans to detect signs of consciousness in people diagnosed as being in a vegetative state, for example, while others have used brain waves to determine when people become unconscious under anaesthesia.
Those experiments fostered an explosion of new theories. To winnow them down, the Templeton World Charity Foundation has begun supporting large-scale studies that put different pairs of theories in a head-to-head test, in a process called adversarial collaboration. And last month, researchers at the New York event unveiled the results of the foundation’s first trial, a match-up of two of the most prominent theories. The first, known as the Global Workspace Theory, holds that consciousness is a byproduct of the way we process information.
Neuroscientists have long known that most of the signals that come from our senses never reach our awareness. Experiments led by Stanislas Dehaene, a cognitive neuroscientist with the College de France in Paris, suggest that we become aware only of signals that reach the pre-frontal cortex, a region in the front of the brain. Dr. Dehaene has argued that a special set of neurons there can quickly relay the information across much of the brain, generating consciousness. “Consciousness is the global availability of information,” Dr. Dehaene said. Dr. Melanie Boly, a neurologist at the University of Wisconsin, came onstage to explain the other contender: the Integrated Information Theory. What makes consciousness special, Dr. Boly argued, is the way it manages to feel at once rich and unified over time. Brains can produce such a phenomenon thanks to the way neurons are arranged, she said.