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Quantum computer/neurocomputer - HameroffNeurocomputer & quantum computerThe brain is both neurocomputer and quantum computer Stuart Hameroff Cognitive Science, 31, (2007) pp. 1034-45 http://blackwellpublishing.com/journal.asp?0953-816X Keywords: quantum computing, microtubules, Max Tegmark, objective reduction This paper is a reply to an article published by Cognitive Science in 2006 criticising the Penrose-Hameroff model of quantum consciousness from the point of view of mainstream consciousness theory (1. Litt et al, 2006). The criticisms make depressing reading for any serious student of consciousness. Not only do they do nothing to plug any explanatory gaps in the mainstream ideas of the previous decade, but they retain a remarkably casual attitude towards any evidence for or against theories that deviate from the mainstream. In much of his paper, Hameroff merely reiterates the long standing proposals of Orch OR, and here we will concentrate on the specific point on which he counter attacks the Litt et al paper. Litt et al advance the now ancient argument that microtubules are widespread in organisms, and if neurons produced consciousness as a function of their microtubules, then large parts of many diverse organisms including plants would be conscious. As many times before, Hameroff points out that neuronal dendritic microtubules differ from other microtubules in several ways. They are much more densely packed than in other cells, and are unique in having mixed polarity, with short microtubules formed into anti-parallel networks (2. Woolf, 1998). Also, the 17 different types of tubulin protein subunits found in neuronal microtubules are more numerous than those found in other microtubules (3. Lee et al, 1986), and Hameroff thinks that this may be connected to information processing. Another golden oldie trundled out by Litt et al is that if Penrose’s objective reduction (OR) were to be true, quantum theory would have to be rewritten. Many in neuroscience and philosophy seems to regard this as a strong argument against Penrose, apparently oblivious of the multiple problems in existing quantum theory, including incompatibility with relativity, lack of description of underlying reality, and lack of clear understanding of the collapse of the wave function. Litt et al revisit the exchange between Max Tegmark (4.) and Hagan, Hameroff and Tuszynski (5.) at the beginning of this decade. They accept the possibility of longer decoherence times than those claimed by Tegmark, but interpret this as only applying to individual tubulin subunits, which are too small to be significant for neural processing. Hameroff counters that Orch OR applies to bundles of dendritic microtubules, and extends to other neurons via gap junctions. Separately to this Hameroff indicates recent studies that show quantum correlations between electrons between neurotransmitters and receptor proteins. (6. Brookes et al, 2006) (7. Kang & Green, 1970), (8. Nichols, 1986), (9. Snyder & Merill, 1965). Litt et al claim that biochemical explanations of anesthesia have surpassed quantum mechanical versions. Hameroff counters by stating that anesthetic gases act via quantum London forces in hydrophobic pockets in receptor and other proteins to inhibit electron resonance. These are quantum mechanical rather than biochemical processes. Hameroff also mentions a more recent extension of the Orch OR theory that claims that the precise global nature of the gamma synchrony in the brain can only be accounted for by long range quantum correlation (10. Freeman & Vitiello, 2006). |
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