The Integrated Information Theory proposes that consciousness arises from the integration of information within a system, and the degree of consciousness depends on the extent of that integration. When consciousness is lost, the core complex of consciousness disintegrates and Φ measures, reflecting integrated information, diminish. Using functional magnetic resonance imaging of global brain networks during tasks and sleep, the authors discovered that a complex within the frontoparietal network remained constant across tasks, but its regional distribution collapsed in early sleep. Φ measures decreased as sleep progressed under limited analysis conditions. These findings align with and support the theory's predictions.
Integrated information theory (IIT) proposes that consciousness corresponds to a measure called Φ, which quantifies the integration of information in a system. Using functional magnetic resonance imaging (fMRI) data from people under propofol anesthesia and during natural sleep, researchers tested whether Φ changes with loss of consciousness. They constructed systems of five functional brain networks and computed Φ from transition probability matrices. During anesthesia, Φ decreased globally and locally as consciousness was lost. During sleep, Φ decreased locally in posterior brain regions. The findings indicate that integrated information in large-scale brain networks is strongly linked to fluctuations in consciousness.
The posterior brain regions, especially the 'hot zone' for phenomenal consciousness, are central to integrated information theory (IIT). This study used fMRI data from the Human Connectome Project and sleep datasets to estimate the 'main complex'—a set of brain elements where information loss is greatest when partitioned hierarchically. The main complex during wakefulness included executive control, salience, and dorsal/ventral attention networks. These networks persisted during sleep, but the amount of information within them and the default mode network decreased during the hypnagogic stage. The findings suggest that a global interconnected structure of major functional networks may form the core of consciousness.