b. 1960 · A portrait
A neuroscientist proposed that consciousness could be measured with a single number, arguing any system that integrates information deeply enough has some degree of experience. In 2023, over a hundred researchers called the theory pseudoscience.
The line above is how his claims were received — by the scientists whose job was to doubt them. It rises as a claim is tested and accepted, and the room brightens with it. It is not a verdict on truth: some accepted ideas are later overturned, and some rejected ones come back. A hollow point is a claim still open.
Tononi proposed that consciousness corresponds to a system's capacity to integrate information in a way that can't be broken into independent parts, publishing the theory's first formal version in BMC Neuroscience and naming the measure phi.
A related tool the theory inspired, the Perturbational Complexity Index, was introduced in 2013 and later tested in brain-injured patients, distinguishing conscious from unconscious states with high accuracy: a clinical result related to the theory, not proof of it.
Over 100 researchers, including cognitive scientist Stephen Fleming among the organizers, signed an open letter calling IIT pseudoscience, arguing it makes untestable claims that had been overstated in media coverage as an already-tested leading theory. Other scientists publicly disputed the label.
Tononi, Koch and colleagues answered in Nature Neuroscience with a formal reply defending the theory's testable predictions and clinical applications. Other researchers replied in turn, arguing for moving past both the theory and the pseudoscience label. The dispute remains open.