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Penrose-Hameroff orchestrated objective-reduction proposal for human consciousness is not biologically feasible

Laura K. McKemmish1, Jeffrey R. Reimers1,*, Ross H. McKenzie2, Alan E. Mark3, and Noel S. Hush4

  • 1School of Chemistry, The University of Sydney, New South Wales 2006, Australia
  • 2School of Mathematics and Physics, The University of Queensland, Queensland 4072, Australia
  • 3School of Chemistry and Molecular Biosciences and Institute for Molecular Biosciences, The University of Queensland, Queensland 4072, Australia
  • 4School of Molecular and Microbial Biosciences, The University of Sydney, New South Wales 2006, Australia

  • *Author to whom correspondence should be addressed. FAX: +61(2)93513329; reimers@chem.usyd.edu.au
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Phys. Rev. E 80, 021912 – Published 13 August, 2009

DOI: https://doi.org/10.1103/PhysRevE.80.021912

Abstract

Penrose and Hameroff have argued that the conventional models of a brain function based on neural networks alone cannot account for human consciousness, claiming that quantum-computation elements are also required. Specifically, in their Orchestrated Objective Reduction (Orch OR) model [R. Penrose and S. R. Hameroff, J. Conscious. Stud. 2, 99 (1995)], it is postulated that microtubules act as quantum processing units, with individual tubulin dimers forming the computational elements. This model requires that the tubulin is able to switch between alternative conformational states in a coherent manner, and that this process be rapid on the physiological time scale. Here, the biological feasibility of the Orch OR proposal is examined in light of recent experimental studies on microtubule assembly and dynamics. It is shown that the tubulins do not possess essential properties required for the Orch OR proposal, as originally proposed, to hold. Further, we consider also recent progress in the understanding of the long-lived coherent motions in biological systems, a feature critical to Orch OR, and show that no reformation of the proposal based on known physical paradigms could lead to quantum computing within microtubules. Hence, the Orch OR model is not a feasible explanation of the origin of consciousness.

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Phys. Rev. E 80, 021912– Published 13 August, 2009
  • Received 15 November 2008

© 2009 American Physical Society

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