The question of whether quantum mechanical phenomena play a functional role in brain activity and the emergence of consciousness remains one of the most controversial yet intellectually stimulating debates at the intersection of physics, neuroscience, and philosophy of mind. This review systematically examines the principal theoretical frameworks proposing quantum-level mechanisms in neural computation, including the Orchestrated Objective Reduction (Orch OR) hypothesis by Penrose and Hameroff, the quantum brain hypothesis of Stapp, quantum coherence models in microtubules, and quantum field theories of consciousness. We critically evaluate the current state of empirical evidence—including recent quantum biology findings, the challenge of decoherence in warm, biological systems, and experimental observations of quantum effects in biological systems—alongside computational models that bridge quantum formalism and neural network dynamics. Furthermore, we discuss the implications of quantum cognition models for understanding perception, decision-making, and memory. Despite significant scientific skepticism, emerging evidence from quantum biology and advanced neuroimaging technologies provides tentative support for quantum processes in neural substrates. We conclude by identifying critical gaps in current knowledge and outlining future research directions that may resolve the debate, including proposals for experimental paradigms using quantum sensing technologies applied to neural tissue. This review aims to serve as a foundational reference for researchers across disciplines approaching the quantum mind hypothesis with scientific rigor.
The question of whether quantum mechanical phenomena play a functional role in brain activity and the emergence of consciousness remains one of the most controversial yet intellectually stimulating debates at the intersection of physics, neuroscience, and philosophy of mind. This review systematically examines the principal theoretical frameworks proposing quantum-level mechanisms in neural computation, including the Orchestrated Objective Reduction (Orch OR) hypothesis by Penrose and Hameroff, the quantum brain hypothesis of Stapp, quantum coherence models in microtubules, and quantum field theories of consciousness. We critically evaluate the current state of empirical evidence—including recent quantum biology findings, the challenge of decoherence in warm, biological systems, and experimental observations of quantum effects in biological systems—alongside computational models that bridge quantum formalism and neural network dynamics. Furthermore, we discuss the implications of quantum cognition models for understanding perception, decision-making, and memory. Despite significant scientific skepticism, emerging evidence from quantum biology and advanced neuroimaging technologies provides tentative support for quantum processes in neural substrates. We conclude by identifying critical gaps in current knowledge and outlining future research directions that may resolve the debate, including proposals for experimental paradigms using quantum sensing technologies applied to neural tissue. This review aims to serve as a foundational reference for researchers across disciplines approaching the quantum mind hypothesis with scientific rigor.
ABSTRACT Recent advances at the intersection of quantum physics, neuroscience, and cognitive science have renewed interest in whether quantum phenomena and quantum‐inspired formalisms can inform models of human cognition and decision‐making. While classical neural and computational models explain many aspects of perception and behavior, they face limitations in accounting for contextuality, order effects, probabilistic reasoning violations, ambiguity resolution, and rapid information integration. This review synthesizes evidence and theoretical frameworks linking quantum‐related principles to cognition, with emphasis on quantum sensing in biological systems, molecular and subcellular quantum‐relevant mechanisms, quantum‐to‐classical transition pathways, quantum‐inspired models of perception and decision‐making, and quantum‐inspired computational approaches. It also extends beyond the probabilistic arm of quantum cognition by considering emerging equilibrium‐based and causal‐logical theories, including mental equilibrium, brain‐universe similarity, mind‐light‐matter unity, quantum emergence, and quantum intelligence. Throughout, the review distinguishes physically instantiated quantum mechanisms from abstract quantum‐like formalisms that model contextuality, mental entanglement, and non‐separable cognitive dynamics without requiring sustained macroscopic quantum coherence in the brain. Finally, it identifies methodological challenges and future directions for advancing quantum cognitive science toward experimentally testable and biologically meaningful theories.
In the mid-1990s, it was proposed that quantum effects in proteins known as microtubules play a role in the nature of consciousness. The theory was largely dismissed due to the fact that quantum effects were thought unlikely to occur in biological systems, which are warm and wet and subject to decoherence. However, the development of quantum biology now suggests otherwise. Quantum effects have been implicated in photosynthesis, a process fundamental to life on earth. They are also possibly at play in other biological processes such as avian migration and olfaction. The microtubule mechanism of quantum consciousness has been joined by other theories of quantum cognition. It has been proposed that general anesthetic, which switches off consciousness, does this through quantum means, measured by changes in electron spin. The tunneling hypothesis developed in the context of olfaction has been applied to the action of neurotransmitters. A recent theory outlines how quantum entanglement between phosphorus nuclei might influence the firing of neurons. These, and other theories, have contributed to a growing field of research that investigates whether quantum effects might contribute to neural processing. This review aims to investigate the current state of this research and how fully the theory is supported by convincing experimental evidence. It also aims to clarify the biological sites of these proposed quantum effects and how progress made in the wider field of quantum biology might be relevant to the specific case of the brain.
As the emerging field of quantum biology matures it is becoming possible to understand the fundamental workings of biological systems at the subatomic level. Understanding the complex function of the brain from this vantage point is no exception. Looking at the subcellular functions of neurons beyond the standard classical mechanisms of chemical and electrical signaling offers the potential to design advanced diagnostics and therapeutics for neurological disorders and mental illnesses based on quantum technologies and could even lead to a more comprehensive understanding of human cognition, behavior, or even consciousness itself. Towards this end there have been many theories proposed for how quantum mechanics may play a role in brain function. However, regardless of how promising these theories are, without experimental evidence to provide validation they are merely interesting conjectures. Here we present a review of current theoretical quantum mechanisms proposed to influence brain function (e.g., spin-based mechanisms, optical mechanisms) and place them in the context of existing experimental evidence. We find that experimental evidence does support quantum mechanisms that may exist in the brain, but significant challenges remain in explaining how such mechanisms may influence processes on relevant biological lengths and timescales. Potential approaches to address these challenges are also discussed.
The mind–matter relationship remained in the domain of philosophers for aeons. However, the inquisitiveness of the scientific minds has always been trying to understand the science behind its various functions. The scientific temper ushered in by the Renaissance about the 15th century saw the scientists exploring this problem from a science point of view. Technological advances during the later part of the 20th century enabled neuroscientists to explore and localise functions of the brain. However, the most difficult has been understanding the origin of a conscious experience scientifically or materialistically. Despite the delineation of many functions of the brain, the origin of conscious experience, the qualia, in the material brain remains elusive, so much so it came to be called the holy grail of neuroscience. Heisenberg wrote: ‘Physics entered the domain of philosophy with the emergence of consciousness in quantum observation, which incidentally opened the door for reconciliation of science and philosophy’,[1] an event which enabled the predictions of Snow of the merging of arts and sciences.[2,3] Quantum mechanics is a branch of physics relating to very small particles – subatomic particles – electrons, photons, and everything in the submolecular realm, being the smallest units in matter. Quantum theory is the most fundamental theory of matter available at present. Some basic concepts of quantum physics need to be understood. These include “superposition”, where in subatomic particles exist either as waves or particles in a dual nature, never simultaneously. They exist as waves in more than one place at a time and once an observer observes or interferes with (such as measuring) their superposition state collapses to particle state. Quantum entanglement is the phenomenon that occurs when a group of particles which are generated, interact with or share special proximity such that they remain connected even when separated by vast distances. Consciousness is a manifestation of quantum process. Q mind or Q consciousness comprises a group of hypotheses proposing that quantum mechanical phenomena such as entanglement and superposition may play an important part in the functions of the brain and could thus explain the origin of consciousness. Several theories of quantum consciousness have been proposed. Wigner proposed the idea that quantum mechanics has something to do with the workings of the mind and proposed that the wave function collapse in the interaction with conscious observation creates consciousness.[4] Vitiello and Freeman[5] proposed quantum field theory (QFT) of brain states. This theory deals with systems and provides formal elements from which a standard description of brain activity can be inferred. According to QFT, particles are only excited states or simply manifestations of a field. Every particle has its own field that covers all of the universe, which means that, according to QFT, all of the electrons of the universe belong to the same field and could be regarded as one. Bohm formulated the QFT as a deeper theory of quantum theory plus relativity.[6] He viewed mind and matter as projections into our explicate order underlying the implicate order. Quantum brain dynamics (QBD) hypothesis explains the function of the brain within the framework of QFT.[7] It is not yet known exactly how quantum superpositions and their collapse result in the genesis of the raw feels of consciousness, the qualia. Feynman stated ‘if you think you understand quantum mechanics then you do not!’[8] Pribram proposed the holonomic brain theory (quantum holography). He invoked quantum mechanics to explain the higher-order processing by the mind. Pribram provided evidence on how much of the processes in the brain take place in a distributed fashion.[9,10] The composite model of Pribram-Bohm of holoflux hypothesis addresses observed phenomenon of non-locality both spacially and temporally. Bose and Einstein, who first predicted Bose Einstein condensate proposed that water at dendritic membrane surfaces might operate by structuring condensation,[11] supporting QBD. Penrose and Hamoreff proposed the orchestrated-objective reduction (ORCH-OR) in 1989 through 2013. According to them, the microtubules in the neurons (neurotubules), the tubulin protein polymer at the site of quantum collapse, leads to conscious experience. The quantum superposed states which develop in the tubulins remain coherent and recruit more superposed tubulins until a mass-time-energy threshold is reached. At this point, self-collapse or objective reduction occurs, which is equated to a discrete conscious event. Cascades of ORCH-OR events give rise to the stream of consciousness.[12,13] Penrose suggested that objective reduction represents neither randomness nor algorithmic processing but instead a non-computable influence in spacetime geometry from which mathematical understanding and, by later extension, consciousness derives.[14] Quantum vibrations in the microtubules proposed by Bandyopadhyay[15] have been shown to be source of conscious experience by corroborating the Penrose-Hemeroff’s ORCH-OR hypothesis.[13,16] In April 2022, the results of two related experiments at the University of Alberta and Princeton University, announced at The Science of Consciousness conference, provided further evidence to support quantum processes operating within microtubules. However, in another experiment, Gregory D. Scholes and Aarat Kalra of Princeton University used lasers to excite molecules within tubulins, causing a prolonged excitation to diffuse through microtubules further than expected, which did not occur when repeated under anaesthesia.[17,18] Beck and Eccles considered quantum mechanics at the synaptic level. If Orchestrated objective reduction (ORCH-OR) theory is applicable, a similar phenomenon in the microtubules at the presynaptic level, the axon terminal could be invoked for the genesis of consciousness.[19] A recent study by scientists at Trinity College, Dublin, in October 2022,[20] suggests that quantum processes underlie the cognitive and conscious brain functions. The brain–mind operational architectonics is the boundary between and integration point of quantum physics and eastern metaphysics and that it may inspire building a richer and more inclusive paradigm of the brain–mind relation, where quantum physics and eastern metaphysics are inherently intertwined. A body of empirical evidence[21-24] supports these possibilities, strengthening the proposal that the mind–brain relationship may be partially quantum. Quantum information theory clarifies the distinction between the unobservable mind and the observable brain and supports a solid physical foundation for consciousness research. With all these theories trying to explain and understand the theoretical/hypothetical framework for consciousness to explain the subjective experience of consciousness, the experts of this field feel it is still a long way to bridge the gap between current neurobiological and physical–mathematical concepts with their associated quantum–mind theories. Though there is still a long way to go for explaining conscious experience scientifically, when ever this happens, it will become one of the benchmarks in science. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. Use of artificial intelligence (AI)-assisted technology for manuscript preparation The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the preparation of the manuscript and no images were manipulated using AI.
Despite centuries of scientific inquiry, the origin of human consciousness, characterized by self-awareness and the presence of qualia, remains one of the deepest mysteries in neuroscience. Orchestrated Objective Reduction (Orch OR), as proposed by Roger Penrose and Stuart Hameroff, posits that consciousness arises from the objective reduction of quantum superpositions within entangled neural microtubules, triggered by gravitational self-energy. Recent theoretical and biophysical studies have renewed interest in quantum coherence in biological systems, including terahertz vibrational measurements, advances in quantum biology, and computational modeling of microtubule dynamics. This review synthesizes these developments and examines major critiques of Orch OR, particularly the challenge of maintaining quantum coherence in warm, wet biological environments. It further introduces the Quantum Cognition Gradient (QCG), a phenomenological, heuristic framework that extends Orch OR by proposing a scalable relationship between cognitive complexity and the formation, persistence, and coordination of quantum-coherent microtubule states prior to objective reduction, while leaving the underlying Diósi–Penrose collapse mechanism unchanged. Finally, several experimental strategies, including terahertz spectroscopy, entanglement-detection assays, interferometric microscopy, and neuromodulatory perturbation studies, are outlined as potential approaches for empirically evaluating predictions of both Orch OR and the QCG framework. By integrating contemporary developments in quantum biology with a quantitative conceptual framework, this review presents Orch OR and the proposed QCG as testable, hypothesis-generating models for investigating the possible relationship between quantum processes and consciousness.
This paper presents a historical perspective on the development and application of quantum physics methodology beyond physics, especially in biology and in the area of consciousness studies. Quantum physics provides a conceptual framework for the structural aspects of biological systems and processes via quantum chemistry. In recent years individual biological phenomena such as photosynthesis and bird navigation have been experimentally and theoretically analyzed using quantum methods building conceptual foundations for quantum biology. Since consciousness is attributed to human (and possibly animal) mind, quantum underpinnings of cognitive processes are a logical extension. Several proposals, especially the Orch OR hypothesis, have been put forth in an effort to introduce a scientific basis to the theory of consciousness. At the center of these approaches are microtubules as the substrate on which conscious processes in terms of quantum coherence and entanglement can be built. Additionally, Quantum Metabolism, quantum processes in ion channels and quantum effects in sensory stimulation are discussed in this connection. We discuss the challenges and merits related to quantum consciousness approaches as well as their potential extensions.