Abstract Brain action, according to the conventional viewpoint, is to be understood in terms of essentially classical physics—or so it would seem. Nerve signals are normally taken to be ‘on or off’phenomena, just as are the currents in the electronic circuits of a computer, which either take place or do not take place—with none of the mysterious superpositions of alternatives that are characteristic of quantum actions. Whilst it would be admitted that, at underlying levels, quantum effects must have their roles to play, biologists seem to be generally of the opinion that there is no necessity to be forced out of a classical framework when discussing the large-scale implications of those primitive quantum ingredients.
Abstract Brain action, according to the conventional viewpoint, is to be understood in terms of essentially classical physics—or so it would seem. Nerve signals are normally taken to be ‘on or off’phenomena, just as are the currents in the electronic circuits of a computer, which either take place or do not take place—with none of the mysterious superpositions of alternatives that are characteristic of quantum actions. Whilst it would be admitted that, at underlying levels, quantum effects must have their roles to play, biologists seem to be generally of the opinion that there is no necessity to be forced out of a classical framework when discussing the large-scale implications of those primitive quantum ingredients.
In classical physics there is, in accordance with common sense, an objective world ‘out there’. That world evolves in a clear and deterministic way, being governed by precisely formulated mathematical equations. This is as true for the theories of Maxwell and Einstein as it is for the original Newtonian scheme. Physical reality is taken to exist independently of ourselves; and exactly how the classical world ‘is’ is not affected by how we might choose to look at it. Moreover, our bodies and our brains are themselves to be part of that world. They, also, are viewed as evolving according to the same precise and deterministic classical equations. All our actions are to be fixed by these equations - no matter how we might feel that our conscious wills may be influencing how we behave. Such a picture appears to lie at the background of most serious 1 philosophical arguments concerned with the nature of reality, of our conscious perceptions, and of our apparent free will. Some people might have an uncomfortable feeling that there should also be a role for quantum theory - that fundamental but disturbing scheme of things which, in the first quarter of this century, arose out of observations of subtle discrepancies between the actual behaviour of the world and the descriptions of classical physics. To many, the term ‘quantum theory’ evokes merely some vague concept of an ‘uncertainty principle’, which, at the level of particles, atoms or molecules, forbids precision in our descriptions and yields merely probabilistic behaviour. Actually, quantum descriptions are very precise, as we shall see, although radically different from the familiar classical ones. Moreover, we shall find, despite a common view to the contrary, that probabilities do not arise at the minute quantum level of particles, atoms, or molecules - those evolve deterministically - but, seemingly, via some mysterious larger-scale action connected with the emergence of a classical world that we can consciously perceive. We must try to understand this, and how quantum theory forces us to change our view of physical reality.
When the revolutionary conceptual structure for the description of the physical world which we know as quantum mechanics was first formulated nearly 90 years ago, and its predictions tested in the laboratory, most of the experiments in question were on systems which were both very well characterized and reasonably well isolated from their environments, such as single electrons and atoms, small molecules and near-perfect crystalline solids. While from the very start most physicists have taken it for granted that the formalism of quantum mechanics, when combined with appropriate system-specific information, can “in principle” account for all phenomena occurring in the physical world, including those usually regarded as the subject-matter of biology, until quite recently the overwhelmingly majority opinion has been that in a biological context the role of quantum theory is confined to elucidating the equilibrium structures of the relevant molecules and their reaction processes, and that subtle phenomena such as superposition and entanglement, of which we can now routinely exhibit spectacular effects at the level of a few well-isolated photons or atoms, play at most a very indirect role in any phenomena of biological interest. A major reason conventionally given for this view has been that biological systems, at least working ones, are by their very nature “warm and wet” – a phrase which in the physicist's lexicon translates to “prone to massive decoherence”; it looks as though any interesting superposition, say of different energy eigenstates of one's system, would be rapidly decohered by the ever-present, and usually microscopically very complex, environment.
Abstract Quantum theory provides a superb description of physical reality on a small scale, yet it contains many mysteries. Without doubt, it is hard to come to terms with the workings of this theory, and it is particularly difficult to make sense of the kind of ‘physical reality’—or lack of it—that it seems to imply for our world. Taken at its face value, the theory seems to lead to a philosophical standpoint that many (including myself) find deeply unsatisfying. At best, and taking its descriptions at their most literal, it provides us with a very strange view of the world indeed. At worst, and taking literally the proclamations of some of its most famous protagonists, it provides us with no view of the world at all.
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.
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.
In recent decades it has become common throughout the social sciences to think of the human mind simply as a very complex computer. Drawing on an older materialist metaphor of the mind as a machine, the “computational” model of the mind took off after the mid-century invention of the computer and subsequent cognitive revolution in psychology, and has since permeated the social sciences in the form of rational choice and other prominent social theories. The contributions of this model have been huge; but it has always been assumed that the computations going on inside our heads are classical. Quantum brain theory challenges this assumption by proposing that the mind is actually a quantum computer. Classical computers are based on binary digits or “bits” with well defined values (0 or 1), which are transformed in serial operations by a program into an output. Quantum computers in contrast are based on “qubits” that can be in superpositions of 0 and 1 at the same time and also interact non-locally, enabling every qubit to be operated on simultaneously. The idea of a quantum computer was first proposed in the 1980s and is still far from being realized technologically, but it has fired the imagination of scientists by raising the prospect of unimaginable increases in computational power, and other neat tricks besides. If quantum brain theory is true, then our model of the mind would be similarly radically altered, irrespective of the issue of consciousness. Quantum brain theory hypothesizes that quantum processes at the elementary level are amplified and kept in superposition at the level of the organism, and then, through downward causation constrain what is going on deep within the brain. On this view, information from the environment is continuously transformed from the macro- to the micro-level, and then channeled back upward into an “internal quantum state,”