4 ideas
Consciousness is identified with integrated information (phi). Phi is the amount of information a system generates as a whole, over and above what its parts generate independently. A system is conscious to the degree that its current state rules out a large repertoire of alternative states (information) and cannot be split into independent parts without losing that information (integration).
The cerebellum has more neurons than the cerebral cortex, yet losing it leaves consciousness essentially intact, while damage to the thalamocortical system can abolish experience. The explanation offered is architectural. The cerebellum is organized as many parallel, largely independent modules with low integration. The cortex is densely interconnected, so it is both highly differentiated and integrated.
A photodiode that distinguishes only light from dark generates just 1 bit of information, so it has minimal experience however reliably it responds. A digital camera sensor with a million photodiodes discriminates vast numbers of images. Its pixels do not interact, so it is a million 1-bit systems rather than one integrated whole, and its phi is near zero. The contrast shows that sheer information capacity without integration does not produce consciousness.
Loss of consciousness in dreamless sleep, anesthesia and generalized seizures occurs even though neurons remain highly active. Integration breaks down or differentiation collapses in these states. In deep sleep, a magnetic pulse to the cortex produces only a local, short-lived response. In wakefulness, the same pulse triggers a complex, widespread pattern. Consciousness therefore depends on the capacity for differentiated, integrated causal interaction, not on the amount of neural firing.