Plain English Summary
What if we could measure consciousness with math? Integrated Information Theory (IIT) attempts exactly that. It starts with five basic truths about what experience feels like and works backward to figure out what kind of physical system could produce it. The key number is called Phi -- essentially a measure of how much a system's parts work together as a unified whole rather than as separate pieces. Here's the stunning part: IIT explains why your cerebellum, which has four times more brain cells than your cortex, contributes basically nothing to conscious experience. It also explains why consciousness vanishes during deep sleep even though your neurons keep firing. Researchers even built a practical tool called the perturbational complexity index that can detect consciousness in patients under anesthesia or with brain damage. For bigger questions -- like whether consciousness could exist outside a normal brain -- IIT offers a rigorous framework that's become central to debates about near-death experiences and mind-matter interactions.
Research Notes
The most mathematically developed current theory of consciousness. Relevant to the library because it provides a principled framework for asking whether consciousness can exist independently of standard neural substrates — central to NDE/survival debates — and for evaluating mind-matter interaction claims. Companion to Tononi & Koch (2015).
Integrated information theory (IIT) starts from five phenomenological axioms — intrinsic existence, composition, information, integration, and exclusion — and derives postulates about the physical substrate of consciousness (PSC). The PSC is the complex of neural elements specifying a conceptual structure with maximum integrated information (Phi_max). IIT explains why the cortex supports consciousness but the cerebellum (with 4x more neurons) does not, why consciousness fades during slow-wave sleep despite continued neural activity, and predicts that consciousness can split in split-brain patients. The perturbational complexity index (PCI), validated across sleep, anesthesia, and brain damage, serves as a practical proxy for Phi_max.
Links
Related Papers
Companion
- Consciousness in the Universe: Neuroscience, Quantum Space-Time Geometry and Orch OR Theory — Penrose, Roger (2011)
- The CEMI Field Theory: Closing the Loop — McFadden, Johnjoe (2013)
- Can Panpsychism Become an Observational Science? — Matloff, Gregory L (2016)
- Weak Quantum Theory: Complementarity and Entanglement in Physics and Beyond — Atmanspacher, Harald (2002)
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📋 Cite this paper
Tononi, Giulio, Boly, Melanie, Massimini, Marcello, Koch, Christof (2016). Integrated Information Theory: From Consciousness to Its Physical Substrate. Nature Reviews Neuroscience. https://doi.org/10.1038/nrn.2016.44
@article{tononi_2015_integrated_information,
title = {Integrated Information Theory: From Consciousness to Its Physical Substrate},
author = {Tononi, Giulio and Boly, Melanie and Massimini, Marcello and Koch, Christof},
year = {2016},
journal = {Nature Reviews Neuroscience},
doi = {10.1038/nrn.2016.44},
}