Dateline: June 25, 2000

Quantum physicics and molecular biology are two disciplines that have evolved relatively independently. However, recently a wealth of evidence has demonstrated the importance of quantum mechanics for biological systems and thus a new field of quantum biology is emerging. Living systems have mastered the making and breaking of chemical bonds, which are quantum mechanical phenomena. Absorbance of frequency specific radiation (e.g. photosynthesis and vision), conversion of chemical energy into mechanical motion (e.g. ATP cleavage) and single electron transfers through biological polymers (e.g. DNA or proteins) are all quantum mechanical effects. Hopefully, the merging of disciplines known as nanotechnology will remove the interface between quantum physics and biology.

In a paper titled 'The Importance of Quantum Decoherence in Brain Processes,'[1] Max Tegmark sought to prove that the brain is too warm to maintain the coherence required for quantum computation. From the results of his calculations, Tegmark claims that, "there is nothing fundamentally wrong with the current classical approach to neural network simulations." This statement contradicts the hypothesis that the brain functions as a quantum computer, originally proposed Roger Penrose[2]. Tegmark's claim was amplified by a recent report in Science beginning with the sentence, 'Sir Roger Penrose is incoherent, and Max Tegmark says he can prove it.'[3] However, the computations carried out by Tegmark relied on a value of 310K for the temperature in his model of the neuron. While the average kinetic energy (temperature) of an entire brain cell may be 310K, the most fundamental characteristic of life is that it is not at equilibrium and thus, our statistical method for measuring temperature breaks down at small sizes, especially at the nanoscale.

Biological systems are known to have ways of manipulating local temperatures. For instance, Koichiro Matsuno has determined by the postulate of black body radiation measurements that actomyosin complexes (abundant in the axons of nerve cells) can reach local temperatures as low as 1.6*10-3K[4]. Matsuno argues that actomyosin functions as a heat engine (a device that converts heat energy into mechanical energy) that is able to maintain a constant velocity due to quantum mechanical coherence and entanglement.

[1] Max Tegmark, 'The Importance of Quantum Decoherence in Brain Processes,' Phys. Rev. E 61 (2000) 4194-4206. homepage.

[2] Roger Penrose, The Emperor's New Mind : Concerning Computers, Minds, and the Laws of Physics, Penguin USA 1991. Amazon.com

[3] Charles Seife, 'Cold Numbers Unmake the Quantum Mind' Science, (Feb. 4, 2000) 287, No. 5454, p791.

[4] Koichiro Matsuno, 'Cell motility as an entangled quantum cohererence,' BioSystems (1999) 51, 15-19. Koichiro Matsuno's Homepage

Keywords: quantum biology physics actomyosin axon coherence entanglement nanotechnology decoherence brain temperature break down nanoscale koichiro matsuno roger penrose max tegmark phys rev E emperors new mind science biosystems computation classical neural network simulation equilibrium black body radiation chemical bond photosynthesis vision ATP electron transfer

It is true that neural network simulations have dramatically improved our computers' abilities for empirical classification and pattern recognition; however, as of now no classical neural network model has the algorithm used by real neurons for determining exactly when to fire (termed activation function), or more importantly exactly when and how much of the neurotransmitters are secreted into the synapse. It is entirely possible that complex computations are carried out within a single neuron, making the brain massively parallel. While on the microscale the axon clearly functions as a kind of wire that propagates an electric current to the synapse, on the nanoscale it serves the purpose of transporting vesicles containing the neurotransmitters required for signal transduction across the synapse.

The vesicles (nanoscale vessels or containers) are transported by the actomyosin molecular motors described on the previous page. Actin and myosin are the two components of actomyosin, which is a ubiquitous complex used for muscle contraction in addition to its vesicle transport function in neurons. One Adenosine Triphosphate (ATP) molecule is used as the molecular fuel for each step made by myosin along the actin filament, resulting in ~60% efficiency of 'chemomechanical power transduction'[5] in muscle cells. The release of energy from the ATP molecule occurs at an extremely slow rate (10-2s/ATP molecule) and is thought to proceed by the emission of a sequence of quanta [6].

The main arguement of Tegmark against the possibility of the brain acting as a quantum computer relied on his caluclation of the decoherence time of a kink in a microtubule being 10-13s. He claimed that since the neuron operates on a time scale between 10-3s and 10-1s, the decoherence is too fast [1]. This may be true for microtubule kinks, but the effective freezing of the myosin engine core operates on the appropriate time scale. Furthermore, Matsuno has determined the momentum of the condensed quantum state from the sliding velocity of the myosin along an actin filament, which yields a de Broglie wavelength of 4.5 nm. Since this length is sufficiently greater than the 2.5 nm diameter of each actin monomer it is likely that the quantum coherence and entanglement extends over several actin monomers aligned along the actin filament [4]. These facts combinded with the near absolute zero effective temperature suggests that the actomyosin vessicle transport system does exibit the quantum coherence and entanglement necessary for quantum computation within a single neuron.

References:

[5] Robert A. Freitas Jr. Nanomedicine Volume I: Basic Capabilities, Landes Bioscience 1999, p 147. Table of Contents

[6] Koichiro Matsuno, 'Being free from ceteris paribus a vehicle of founding physics upon biology rather than the other way around' Appl. Math. Comp. (1993) 56, 261-279. Koichiro Matsuno's Homepage

Keywords: quantum biology myosin coherence neural network simulation massively parallel nanoscale vessicle transport signal transduction actomyosin molecular motors actin ATP adensine triphosphate chemomechanical power transduction rate freitas matsuno neuron quantum computation

While most biochemical studies of actomyosin and other proteins ignore the delicate nature of quantum mechanical effects such as superposition, coherence and entanglement, there is much to be gained from such models. For instance, regulatory molecules and pharmaceuticals may interact with the protein not only as a lock and key, but as several locks and several keys. However, the exact geometry of the super cooled region of this ATP bound engine (figure 1), upon which the coherence and entanglement would depend, is not known. Although quantum mechanical models of proteins are currently too computationally complex for our fastest supercomputers, molecular dynamics simulations may help to illucidate the mechanisms by which the heat is pumped out of the frozen core, thus illucidating the boundry of the coherence. Novel biophysical methods resulting from the fusion of biology and quantum mechanics have the potential to revolutionize our understanding of both fields.

As biologists begin to realize the importance of nanoscale phenomena to their research, quantum biology is emerging as an important discipline. At a time when numerous physicists are racing to construct quantum computers, molecular biologists may unknowingly be racing to dismantle them.

"Biology is not about applying quantum mechanics as it is already known through the experiences of traditional physics, but rather about an attempt to extend quantum mechanics in the manner that the physicists have not tried." [8]

Acknowledgements - Thank you Koichiro Matsuno for reviewing the text and for the enlightening comments.

[7] Gulick AM, Bauer CB, Thoden JB, Rayment I, 'X-ray structures of the MgADP, MgATPgammaS, and MgAMPPNP complexes of the Dictyostelium discoideum myosin motor domain.' Biochemistry (Sep 30, 1997) 36 (39), 11619-28.

[8] Koichiro Matsuno, Raymond C. Paton, 'Is there a biology of quantum information?' BioSystems (2000) 55, 39-46.

Keywords: quantum biology actomyosin myosin engine domain figure molecular simulation ATP lock and key computer novel biophysical methods physics matsuno paton biosystems super cooled coherence entanglement pharmaceutical superposition rasmol model image graphic gulick x-ray structures