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Quantum mind is the idea that large-scale quantum coherence is necessary to understanding the brain.
This is very much a minority opinion, although it does have the support of the well-known mathematical physicistRoger Penrose. Other proponents include Stuart Hameroff, Karl Pribram, and Henry Stapp. The argument for quantum mind is the argument that classical mechanics cannot explain consciousness.
The main argument against the quantum mind is that the brain is warm, wet, and noisy and that the structures of the brain are much too large for quantum mechanics to be important. Consequently, it is difficult for coherent quantum states to form for very long in the brain, and impossible for them to exist at the scales on the order of the size of neurons. These issues have led Penrose to argue that consciousness is not a consequence of interactions betweenneurons in the brain but arises as from microtubules within cells, which are much smaller and for which quantum effects could be significant.
This view is very different from conventional views of how the brain works, in which neurons communicate via electric impluses which trigger the release of neurotransmitters in the synapses. In the conventional view of brain function, microtubules play no significant role in brain function other than to provide structural support to the neurons. The theory of the quantum mind has been criticized on a number of grounds. For one, it fails to explain how chemicals and physical processes which effect neuron functioning would cause generally predictable changes in consciousness, whereas the conventional theory provides an explanation for how psychoactive substances work and how the brain would react to injury. In addition, microtubules are found in all cells, not just neurons, and no reason has been given why consciousness should be influenced by neuron microtubules, and not those in other parts of the body. Also,decoherence mechanisms such as emission of thermal radiation appear to apply to large molecules such as microtubuleprotein subunits and synaptic vesicle proteins, making quantum coherence on the size scale proposed for quantum mind theories unlikely.