Extracted from a consistently fascinating post on quantum computation and consciousness by Scott Aaronson:
Yes, consciousness is a property of any suitably-organized chunk of matter. But, in addition to performing complex computations, or passing the Turing Test, or other information-theoretic conditions that I don’t know (and don’t claim to know), there’s at least one crucial further thing that a chunk of matter has to do before we should consider it conscious. Namely, it has to participate fully in the Arrow of Time. More specifically, it has to produce irreversible decoherence as an intrinsic part of its operation. It has to be continually taking microscopic fluctuations, and irreversibly amplifying them into stable, copyable, macroscopic classical records.
The immediately subsequent clarification is also crucial: “let me be extremely clear about what this view is not saying. Firstly, it’s not saying that the brain is a quantum computer, in any interesting sense — let alone a quantum-gravitational computer, like Roger Penrose wants! Indeed, I see no evidence, from neuroscience or any other field, that the cognitive information processing done by the brain is anything but classical.”
Once seen, this is an argument that cannot be unseen. (It’s almost an instance of consciousness-production through ratcheted decoherence in itself.)