A Warm and Wet Brain does not preclude Quantum Processing

The idea that quantum mechanics is somehow connected to consciousness has a long history. In the 1960s physicist Eugene Wigner, building upon an earlier idea articulated by John von Neumann1 in 1932, proposed that consciousness plays a fundamental role in the quantum measurement process by causing the collapse of the wavefunction. Henry Stapp later argued along similar lines that quantum mechanics could play a role in decision-making and free will. These early proposals were more philosophical and did not propose or entail concrete biological mechanisms for how quantum effects might occur. In the 1990s Roger Penrose and Stuart Hameroff proposed a specific physiological mechanism in their theory of Orchestrated Objective Reduction2 (Orch-OR). According to Orch-OR consciousness consists of a sequence of discrete events of the objective reduction of quantum states arising from quantum computations in neuronal microtubules. More recently, Matthew Fisher3, Professor of Theoretical Physics at the University of California Santa Barbara, has investigated a different possible biochemical mechanism for quantum processing in the brain, which he discusses in the C&R colloquium held on 2025, February 12th. 

In a nutshell Fisher asks whether we, or more precisely our brains, might be quantum computers rather than what he calls “clever robots”4. His research tries to answer this question in the affirmative and to develop a theory with experimentally testable predictions. Fisher’s idea is that nuclear spins in the brain could serve as biological qubits, enabling quantum information processing in ways previously unimagined. A qubit, or quantum bit, is the fundamental unit of quantum information. Unlike classical bits, which can be either 0 or 1, qubits can exist in a quantum mechanical superposition of both states simultaneously. This allows quantum computers to process complex calculations exponentially faster than classical computers. Qubits also exhibit entanglement, meaning the state of one qubit can be correlated with another, no matter how far apart they are. This entanglement is critical to the operation of a quantum computer. A key challenge is how to maintain entanglement in the noisy environment of a human brain.

Fisher's journey into this field began not with quantum mechanics but with lithium, a common psychiatric drug used to treat bipolar disorder. Lithium exists in two stable isotopes: lithium-6 and lithium-7. These differ only by one neutron, meaning their chemical properties should be virtually identical. Yet, experiments on rats have shown that lithium-6 and lithium-7 produce dramatically different behavioural effects. Typically, isotopic differences in biology are attributed to mass variations, which can influence reaction rates, but the mass difference between these lithium isotopes is too small to account for such pronounced effects. This led researchers to consider nuclear spin as a possible factor, since lithium-6 has a nuclear spin of 1 while lithium-7 has a spin of 3/2. If biological systems are sensitive to nuclear spin states—potentially through quantum effects—this could explain why the two isotopes yield distinct neurobehavioral outcomes.

This led Fisher to ask a broader question: Could nuclear spins in the brain play a role in cognitive processes? If so, how could such delicate quantum states persist in a biological environment? To explore this, he examined the potential role of nuclear spins in biochemical reactions. The key to Fisher's hypothesis is the phosphorus-31 nucleus, which has a spin-1/2 state and is common in biological molecules. Under the right conditions, phosphorus atoms can be part of calcium phosphate clusters known as Posner molecules, which may provide a protective environment that shields nuclear spins from decoherence. Decoherence is the process by which quantum systems lose their coherence due to interactions with their environment. In biological systems, decoherence is a major challenge, as the warm and wet nature of the brain should theoretically disrupt any quantum effects. Fisher proposes that these Posner molecules could form entangled networks within mitochondria and potentially influence neural activity through calcium signalling (see Fig. 1 and Fig. 2).

In a biological setting, the potential for nuclear spin coherence is remarkable. While conventional neuroscience assumes that synaptic transmissions and action potentials are purely classical, Fisher’s model suggests that long-lived quantum coherence in Posner molecules could regulate neuronal function. If true, this would introduce a radically new paradigm for brain computation.

Fisher's theory is supported by several past and ongoing experimental studies, including:

• Lithium Isotope Effects: Both behavioural studies in rats and mitochondrial calcium uptake experiments have shown significant differences between lithium-6 and lithium-7, supporting the idea that nuclear spin states can impact biological processes.

• Posner Molecule Stability: Fisher has proposed theoretical models suggesting that Posner molecules, clusters of calcium and phosphate ions, could protect nuclear spins from decoherence, potentially allowing for quantum information processing in the brain. Light-scattering experiments indicate that Posner molecules can form under physiological conditions, and their properties suggest they might harbour long-lived quantum coherence.

• Chemical Reaction Rates and Nuclear Spin: Preliminary data suggest that nuclear spin states may influence the binding and dissolution rates of Posner molecules, providing a potential mechanism for quantum information processing in the brain.

If nuclear spin coherence and entanglement indeed play a role in brain function, this could have profound implications for our understanding of consciousness. Fisher speculates that quantum entanglement within and between mitochondria might enable non-local information processing within neurons. However, whether this could scale up to explain cognitive functions such as memory, perception, or even qualia remains an open question.

The discussion after the talk featured a number of thoughtful critiques and questions. One question concerned the possibility of inter-neuronal entanglement. If quantum effects are real in mitochondria, how do they influence large-scale neural processes? Can entanglement extend beyond single neurons to coordinate activity across brain networks? Another question was whether the brain employs mechanisms analogous to quantum error correction to maintain coherence over meaningful timescales. Quantum error correction is a method used in quantum computing to counteract decoherence and maintain stable quantum states. If the brain harnesses quantum computation, it might employ some biological equivalent of quantum error correction to preserve coherent information processing. 

The implications for AI were also discussed. If quantum processing is necessary for consciousness, does this mean classical artificial intelligence can never truly replicate human awareness? Could future quantum computers exhibit forms of cognition that more closely resemble human intelligence?

Further questions explored more deeply the connection with consciousness and implications for AI. Even if quantum effects occur in the brain, does this mean they contribute to consciousness, or are they merely another layer of neural computation? At its core this relates to the hard problem of consciousness – can subjective experience emerge from physical processes, whether classical or quantum? Perhaps something entirely different is really needed to make us more than “clever robots”.     

References

1. Von Neumann discusses the connection between quantum mechanics and measurement—including the potential role of consciousness—in Chapter VI: The Measuring Process of Mathematical Foundations of Quantum Mechanics (1932). He formalizes the von Neumann chain, where the measurement apparatus itself becomes entangled with the quantum system, requiring an external observer to collapse the wavefunction.

2. For a more recent review of Orch-OR see: Hameroff, S., & Penrose, R. (2014). "Consciousness in the Universe: A Review of the 'Orch OR' Theory." Physics of Life Reviews 11(1), 39-78.

3. Fisher first described his theory in detail in: Fisher, M. P. A. (2015). "Quantum Cognition: The possibility of processing with nuclear spins in the brain." Annals of Physics, 362, 593-602.

4. Fisher wrote an article based on a talk addressing precisely this question: Fisher, M. P. A. (2017). "Are we quantum computers, or merely clever robots?" International Journal of Modern Physics B, Vol. 31, No. 7, 1743001.