Quantum Cognition and Quantum Brain Dynamics: Modeling Room-Temperature Coherence in Neural and Retinal Systems

Abstract

Macroscopic biological entities, such as the retina and the human brain, as well as the whole organism, are required to be continuously coherent at room temperature, which is a huge challenge for modern quantum mechanics. Biological tissue is warm, wet and noisy, and this is theoretically expected to result in rapid decoherence, but growing paradigms in quantum cognition and quantum biology indicate that the neural systems somehow avoid immediate collapse induced by environment. One of the unsolved problems in this area is the exact mechanism of how cellular structures are able to remain decoherence-free and support potentially functional quantum states. The aim of this paper is to answer this salient research gap by proposing a theoretical framework for modelling the phenomenon of quantum entanglement and non locality in the brain cell microtubules and retina photoreceptors. Combining the elements of the resource theory of quantum coherence and open quantum dynamics, we propose a formalism that opens the way towards a structured approach, which maps the dipole interactions at the macroscopic scale of biological systems onto Heisenberg spin Hamiltonians. The synthesis yields a mathematical framework for simulating the dynamics of specialized biomolecular architectures likely to protect quantum states from thermal degradation, contributing a critical step toward gaining insight into the quantum-mechanical basis of cognitive and sensory processing.

Introduction

The coherent superposition of states is one of the most basic properties that distinguishes quantum from classical physics, and is now known not only as a theoretical puzzle, but also as a measurable physical resource [1]. The idea that biological systems could harness the magic properties of quantum coherence to facilitate incredible efficiencies in energy transfer and sensory reception has become an interdisciplinary hot topic in recent years. But modern quantum theory does not have an easy solution to the problem of maintaining such fragile quantum states at room temperature in structures such as the human brain, or the mammalian retina. The general opinion is that thermal fluctuations, which are a property of biological systems, should quickly destroy any macroscopic quantum phenomena by rapidly collapsing quantum superpositions into classical statistical mixtures.

Even with these thermodynamic limits, the issue of how neural systems could prevent their rapid decoherence is still an open question in quantum biology and cognitive science. Theoretical models, including Quantum Brain Dynamics (QBD), propose that the coherence of complex quantum states could be influenced by highly ordered cellular structures, but measuring the dynamics of coherence in such systems is highly challenging mathematically and physically. The key research question is the quantum modeling of entanglement and non-locality in these particular biological structures, such as the complex lattices of brain cell microtubules and the densely packed discs of retinal photoreceptors. This is a fundamental question: Do special molecular structures create local protective environments from thermal noise? We must go beyond the realm of conventional classical biophysics to answer that question.

Although the theoretical and experimental studies of quantum coherence have yielded some useful insights, several problems have so far prevented most existing theories and experiments from tackling these biological enigma. First, most of the existing techniques for controlling coherence, including the use of impurity atoms or extreme isolation [2] are only applicable to very cold and carefully controlled environments such as Bose-Einstein condensates. Secondly, the macroscopic thermodynamic models are unable to account for the non-equilibrium, transient dynamics needed to maintain multipartite entanglement in a cell matrix that is continuously fluctuating [3]. There is no comprehensive framework that can go from individual molecular dipoles to large-scale neural signaling pathways, which severely restricts our ability to study quantum cognition on an empirical basis.

In order to overcome these deep shortcomings, this paper proposes an extensive theoretical perspective to serve as a link between rigorous quantum resource theories and complex neurobiological structures. The key findings of this work are summarized as follows:

We suggest an innovative, multi-layered modeling approach of electric dipole interactions of biological water molecules in microtubules that is mapped to a generalized Heisenberg spin Hamiltonian, allowing for the simulation of collective quantum states.

We propose a hypothetical evaluation benchmark for open quantum dynamics which mathematically singles out the decoherence-shielding properties of retinal photoreceptor networks, and prove how continuous coherence can be quantified with simulated thermal noise.

Related Work

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There has been a very rapid progress in the development of rigorous mathematical framework for quantifying quantum coherence, coherence as a fundamental operational resource similar to entanglement [1]. Different "faithful" measures have been developed to define how quantum states can be used to process information [4]. The hierarchical structure of quantum coherence in multipartite systems has also been studied in which researchers discovered that there are complex relationships between quantum coherence, quantum discord and entanglement [3]. Although these resource theories offer mathematically sound means of comparing different coherence measures for various quantum states [5], a significant aspect of their abstraction is that they are mostly formulated for idealized quantum information tasks. In comparison to the current work, these abstract resource measures are then put into the context of a much more concrete and non-ideally designed wet biological environment where we try to interpret the theoretical coherence bounds in terms of measurable parameters of biomolecular lattices.

Open Quantum Dynamics, Thermal Decoherence

The dynamics of the quantum system in noisy environments is of utmost importance, and it has been a subject of a wide range of investigations on open quantum dynamics and thermal decoherence mechanisms. In recent years, progress has been made in characterising quantum coherence dynamically as the mean rate of evolution of a system driven by any Hamiltonian [6], and in this way the speed of the evolution can be bounded in open dynamics. Moreover, when heat noise is extremely high, like Unruh radiation in relativistic contexts, it is shown that coherence can be more robust than entanglement, and is only asymptotically destroyed under extreme conditions [7]. Analogies with classical thermodynamic work are also drawn in the study of quantum coherence vs. thermodynamics using fluctuation relations [8]. These models are very good at establishing the limits of decoherence in the presence of external noise, but are mostly considering abstract or cosmological thermal baths. The approach we take is different in that we confine these open quantum dynamics to the biochemical thermal noise characteristics of human sensory and neural tissues.

 Quantum Brain Dynamics and Spin Models

The use of quantum field theory for biological neural networks began with the theory of Quantum Brain Dynamics (QBD), which proposes that the brain functions through the spontaneous symmetry breaking of macroscopic quantum states. A first mathematical achievement in this area was to show how the QBD model, which was first developed around the corticon and stuarton variables, could be formally mapped onto a Heisenberg spin Hamiltonian [9]. Here, the electric dipole fields produced by the brain's water molecules are considered as the spin variables that interact with the electromagnetic fields [9]. One of the most powerful features of this method is that it offers a familiar and rigorous formalism of physics (spin lattices) which can be used to describe otherwise mysterious biological phenomena. Both of these are significant drawbacks of traditional QBD, however, because it remains largely disconnected from sensory input systems and it has not yet been able to incorporate modern multipartite entanglement measurements. This paper extends the Heisenberg spin foundation to include retinal photoreceptor networks, to connect external photonic stimuli directly to internal quantum cognitive models.

 Method/Approach

Here we suggest a three-level theoretical framework to systematically discuss the maintenance of quantum coherence in neural and retinal systems operating at room temperature. This architecture includes both structural biological mapping and open quantum system dynamics, and rigorous coherence quantification. This is based on the assumption that the highly ordered biological structures of the microtubules and outer segments of the photoreceptors act similarly to synthetic decoherence-shielding topologies. We aim to move the discourse of quantum cognition from speculative philosophy to computable biophysics by organizing it in mathematically formulated modules. The steps aim to gradually extend from the level of interactions at the molecular scale to the scale of collective quantum phenomena, which are organized in a network.

The first module is devoted to the structural mapping of brain cell microtubules with the spin Hamiltonian formalism of Heisenberg. We start from the preceding theories and consider the confined molecules of water inside the tubulin protein cylinders as a quantum spin system with a high degree of correlation [9]. The electric dipole moments of these molecules are presented as spins on a cylindrical lattice. The Hamiltonian includes nearest neighbor exchange interactions which describe the hydrogen bonding network and a coupling term with the local endogenous electromagnetic field. A crucial design is the parameterization of the coupling constants to mimic the actual physical sizes of mammalian microtubules, which allows us to simulate the possibility of spontaneous symmetry breaking to create theoretically long-range order that is able to resist the immediate effect of thermal perturbations.

The second module generalizes this paradigm to the mammalian retina, modeling the retina's photoreceptor cells as a multipartite entanglement network. We suppose that the first energy absorption by the photo-receptive molecule creates a localized coherent superposition when the photon hits the rhodopsin molecules of the tightly packed disc membranes of a rod cell. To model this, we make use of the mathematics of quantum coherence in multipartite systems, using basis-free coherence measures and quantum discord as tools to monitor the propagation of the signal [3]. Finally, we model the rhodopsin lattice as a biological analog of mesoscopic ring-shaped structures in which quantum interference effects may allow for effectively implementing ultra-fast energy transfer without loss before classical signal transduction mechanisms are activated [10].

The third module is for the purpose of simulating an open quantum system and modelling decoherence shields. Using the dynamical characterizations of quantum coherence, we estimate the average evolution rate of the quantum states of the biological entity, and compare its value to the detrimental effect on the evolution of the quantum states due to thermal noise in the cell [6]. We solve the density matrix of the microtubule and retinal systems from a modified Lindblad master equation, where the surrounding cellular cytoplasm is modeled as an interacting thermal bath. We conjecture that the periodic and rigid geometry of these structures is a topological protection mechanism that dynamically suppresses some decoherence channels in biology. This is similar to the use of a single impurity atom to manipulate quantum coherence in a Bose-Einstein condensate, but in this case, it is the geometry of the molecules that is used to that end.

To test this theory we present a detailed evaluation plan, based on a set of hypothetical benchmarks, called "Quantum-Bio-Decoherence-Bench" (QBDB). QBDB will be synthetically created through the use of complex molecular dynamics simulations of the tubulin and rhodopsin structure at 300K and in vivo measurement of multipartite entanglement in human brains is currently not possible. We will test our model by comparing the relative entropy of coherence and the $l_1$ norm of coherence in the range of femtoseconds to picoseconds [5]. The success of the model will be the ability to provide examples of sustained non-zero quantum coherence and geometric quantum discord for time periods long compared to those expected from classical thermodynamic degradation models [4].

 Discussion

Room-temperature quantum coherence in neural and retinal systems would have very far-reaching implications for both biology and engineering. Such a discovery would have profound implications for the development of bio-inspired technologies, as it would lead to the creation of novel quantum systems capable of mimicking the sensory processing and cognitive functions of biological organisms. Engineers can create new room temperature quantum sensors capable of unprecedented sensitivities, without the need for cryogenic cooling apparatuses, based on retinal photoreceptors. Beyond that, studying quantum dynamics of microtubules could also be crucial to the field of neural engineering and medicine, as it could provide insights into the connection between a loss of coherence in cells and cognitive loss associated with neurodegenerative diseases.

Although the theoretical potential, there are several drawbacks and potential pitfalls of this approach. 

First, the computational difficulty of solving the Heisenberg spin Hamiltonian for a multipartite system as big as a macroscopic microtubule lattice is enormous, and may be impractical even for the next generation of quantum computers. 

The second one is that there is no significant amount of experimental information that is precise enough to tell us exactly what the dipoles within biological water are coupled to, and hence our mathematical models can only use guessed values of parameters which may not represent real biological conditions. 

Thirdly, even with the strong thermal noise present at 300K, irreversible degradation of quantum coherence [7] may occur at a time scale too short to be of functional relevance to biological processes.

Ethically and socially, the progress of quantum brain dynamics has significant potential risks that must be taken into account. 

First, epistemic misappropriation is very real, and if any quantum effects are observed in the brain, they can easily be misinterpreted by the pseudoscientific fandom to claim that consciousness or telepathy are quantum phenomena. 

Furthermore, once the bioquantum coherences are successfully reverse engineered, they will give rise to quantum brain-computer interfaces that will represent a massive threat to privacy and security, allowing for unprecedented access into the mind and creating serious neuroethical questions about mental autonomy.

Further research is needed to connect theory and experiment. A major goal will be the development of non-invasive spectroscopic methods with ultrafast speeds that will be able to detect transient multipartite coherence [3] in living cultures of cells. Further future work should investigate the thermodynamic expense of sustaining these biological quantum batteries, possibly through the application of quantum fluctuation relations to the understanding of metabolic energy costs of sustained cellular coherence [8]. With constant updates to these models, the scientific community will eventually be able to interpret the quantum mechanical "language of the human mind".

Conclusion

One of the most intriguing unsolved paradoxes in contemporary biophysics is the longevity of quantum coherence in warm, wet body systems as found in human neural and sensory processes.One of the most interesting anomalies that still remains to be solved in modern biophysics is the fact that quantum coherence is preserved in warm, wet body systems such as human neural and sensory systems. In this paper, a comprehensive theoretical framework was described that explains the possible ways of achieving rapid decoherence at room temperature for structures such as brain microtubules and retinal photoreceptors. We have mapped the biological dipole networks onto Heisenberg spin Hamiltonians and used advanced metrics from the resource theory of quantum coherence to create a route to mathematically query the limits of quantum biology. 

Finally, the research problem of biological entanglement can only be addressed by going beyond idealized isolated quantum models and into the messy and open dynamics of living cells. The challenges involved in both the methodology and the proposed hypothetical benchmarks are very large, but they do provide a baseline for future explorations. With the ability to measure and simulate more and more multipartite quantum states, the idea that functional quantum coherence could also be the basis of macroscopic biological systems could change our understanding of cognition, sensory perception, and even life in general.

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