A critical assessment of the information processing capabilities of neuronal microtubules using coherent excitations |
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Authors: | Travis John Adrian Craddock Jack A Tuszynski |
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Institution: | (1) Department of Physics, University of Alberta, Edmonton, AB, Canada, T6G 2G6; |
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Abstract: | Evidence for signaling, communication, and conductivity in microtubules (MTs) has been shown through both direct and indirect
means, and theoretical models predict their potential use in both classical and quantum information processing in neurons.
The notion of quantum information processing within neurons has been implicated in the phenomena of consciousness, although
controversies have arisen in regards to adverse physiological temperature effects on these capabilities. To investigate the
possibility of quantum processes in relation to information processing in MTs, a biophysical MT model is used based on the
electrostatic interior of the tubulin protein. The interior is taken to constitute a double-well potential structure within
which a mobile electron is considered capable of occupying at least two distinct quantum states. These excitonic states together
with MT lattice vibrations determine the state space of individual tubulin dimers within the MT lattice. Tubulin dimers are
taken as quantum well structures containing an electron that can exist in either its ground state or first excited state.
Following previous models involving the mechanisms of exciton energy propagation, we estimate the strength of exciton and
phonon interactions and their effect on the formation and dynamics of coherent exciton domains within MTs. Also, estimates
of energy and timescales for excitons, phonons, their interactions, and thermal effects are presented. Our conclusions cast
doubt on the possibility of sufficiently long-lived coherent exciton/phonon structures existing at physiological temperatures
in the absence of thermal isolation mechanisms. These results are discussed in comparison with previous models based on quantum
effects in non-polar hydrophobic regions, which have yet to be disproved. |
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Keywords: | Microtubules Information processing Coherent excitations Quantum coherence Phonons Excitons |
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