Giulio Tononi
Neuroscience · mathematical theory of consciousness
Kernel
Tononi is the figure who has tried to make consciousness a measurable quantity. Integrated Information Theory (IIT, 2004 onward) defines a single mathematical scalar Φ that measures how much a system's whole exceeds the sum of its parts in informational integration, and claims that this quantity is consciousness.
Contribution
IIT 1.0, 2.0, 3.0, 4.0 — the successive refinements of the theory. The PCI (perturbational complexity index) as a clinically-useful proxy for consciousness, now used to assess vegetative-state patients. The claim that consciousness is identical to integrated information, not merely caused by it.
Civilization-scale significance
If IIT is correct, consciousness has a measurement. That is one of the largest possible structural shifts in our understanding of mind. If IIT is incorrect, it still demonstrates that consciousness can be approached mathematically — a possibility that pre-Tononi philosophy of mind largely denied.