Reply to Hameroff from Emmet Spier and Adrian Thomas

Abstract

We thank Stuart Hameroff for detailing the intellectual history of the Orch OR model. However, re-rooting its foundations in a form of monism begs more questions than it answers. Even ignoring the problematic conclusion that—then—all forms of matter (rocks, air, grass, protozoa etc.) have minds, we still find it hard to understand how his mind-component of matter influences the substance-component of matter. Either its influence is local—in which case `learned behaviour' and `intensity of deterministic drives' would be neural juggernauts affected by rain drops—or global, in which case our previous, single-Platonic-mind criticism still stands.Neither are we convinced that the mechanistic side of the brain is a computer, even less a quantum computer. A computer manipulates memory elements. Merely identifing the memory elements (qubits) as `microtubule quantum superpositions' completely ignores the fact that machinery must exist for these bits to be fetched, processed and re-stored. This is the job of the central processing unit (CPU) and is wholly ignored in models of the brain as a computer. We also note that there is nothing particularly useful about being a quantum computer, unless factorizing large numbers[1xPolynomial-time algorithms for prime factorization and discrete logarithms on a quantum computer. Shor, P. SIAM J. Comp. 1997; 26: 1484–1509CrossrefSee all References][1](their one establised novel capacity) is a fundamental process of mind.Hameroff agrees with Bray's conclusions that protein molecules are the basic operational elements in living cells, but goes on to suggest that quantum mechanics might play some role too. Bray[2xProtein molecules as computational elements in living cells. Bray, D. Nature. 1995; 376: 307–312Crossref | PubMedSee all References][2]has clearly demonstrated that chemistry is sufficient to explain the complex behaviour of single-celled organisms such as E. coli. Furthermore, mutations that alter the chemistry of E. coli's proteins change its behaviour in ways that are predictable from the effect of the mutations on protein chemistry. Conventional chemical mechanisms can explain how single cells process such information—invoking the Orch OR model is neither necessary nor justified.We also note that Hameroff has suggested that the emergence of consciousness in primitive metazoans (worms) might explain the Cambrian explosion. However, recent fossil finds have reduced the Cambrian anomaly. Papers[3xThree-dimensional preservation of algae and animal embryos in a neoproterozoic phosphorite. Xiao, S., Zhang, Y., and Knoll, A.H. Nature. 1998; 391: 553–558Crossref | Scopus (446)See all References, 4xPrecambrian sponges with cellular structures. Li, C-W., Chen, J-Y., and Hua, T-E. Science. 1998; 279: 879–882Crossref | PubMed | Scopus (309)See all References]describe 570 million-year-old (Precambrian) fossils of metazoan embryos; such fossil finds establish that metazoans originated long before the Cambrian explosion[5xThe breath of life: did increased oxygen levels trigger the Cambrian Explosion?. Thomas, A.L.R. Trends Ecol. Evol. 1997; 128: 44–45Abstract | Full Text PDFSee all References][5], but these Precambrian animals did not fossilize.Crucial to the Orch OR model is the idea that `brain microtubules are quite stable' and that they can maintain some thermal isolation from the rest of the body. This is a misconception. Microtubules in the axons of neurons (but not in the dendrites or cell body) are indeed held in a stable configuration; but even in axons the microtubules turn over at high rates and being shorter than the axon their open ends are exposed to the cell contents[6xSee all References, 7xMicrotubule transport from the cell body into the axons of growing neurons. Slaughter, T., Wang, J., and Black, M.M. J. Neurosci. 1997; 17: 5807–5819PubMedSee all References]. The fluid-filled lumen of microtubules can act as a transport route—for example, during bacterial sex, DNA is transported down the centre of a microtubule-like protein[6xSee all References][6]. It seems unlikely, when molecules as large as DNA, let alone water, can flow through microtubules, that they could possibly maintain the thermal isolation that is an essential requirement for the Orch OR model.Indeed, `how many roads must a man walk down before you call him a man?'—possibly, according to the Orch OR model, `the answer [might well be] blowing in the wind'[8xSee all References][8].