Abstract

Integrated information theory (IIT) starts from the essential properties of experience and translates them into requirements that any physical system must satisfy to be conscious. It argues that the physical substrate of consciousness (PSC) must constitute a maximum of irreducible, internal cause‐effect power of a specific form, and provides a calculus to determine, in principle, both the quality and the quantity of an experience. Applied to the brain, IIT predicts that the spatio‐temporal grain of the neural units constituting the PSC, and the relevant neural states, are those that maximize cause‐effect power. Moreover, the PSC can shrink, move, split and disintegrate depending on various anatomical and physiological parameters. These predictions are testable with brain stimulation and recording experiments. The theory can explain parsimoniously many known facts about the relationship between consciousness and the brain, including its association with certain cortical structures, its breakdown in deep sleep, anesthesia and seizures, and its return in dreams.