1997 Volume 4 Issue 3 Pages 3_67-3_92
Understanding consciousness as neural-level computation faces three problems: First, this approach generally overlooks certain brain features: a) “probabilistic” neurotransmitter release, b) dendritic microprocessing, c) electrotonic gap junctions, d) variability in reaction times/inherent apparent randomness, e) glia, and f) the role of intraneuronal cytoskeletal microtubules. The second problem is computation itself. Present-day computers may be evolving toward quantum computing, in which elements compute in quantum superposition of different possible states (“qubits”), and reduce (collapse) computably to a solution. If the brain/mind is anything like a computer, it is most likely some kind of self-organizing quantum computer. The third problem is the inability of conventional neural approaches to deal with the problem of conscious experience, or qualia (as well as unitary binding, free will, non-computability, and the transition from pre-conscious to conscious processes). New approaches are needed. The Penrose-Hameroff model suggests that quantum superpositions and Penrose's objective reductions occur in microtubules in groups of brain neurons and glia interconnected by gap junctions. The proposed microtubule quantum states and cycles of self-collapses are isolated by actin gelation, orchestrated by microtubule-associated proteins, and coupled to neural-level activity (e.g. coherent 40 Hz). The model predicts that the orchestrated objective reduction (“Orch OR”) events access and select “funda-mental” experience embedded in Planck scale spacetime geometry, and choose (non-computably) microtubule states which regulate neural activity. Consciousness may involve neurobiological processes extending downward within neurons to the level of the cytoskeleton, and accessing fundamental experience at the most basic level of reality.