Quantum Measurement by Quantum Brain

Gustavo Deco, Yonatan Sanz Perl, Natasha Greenstein +3 more

Emerging research provides evidence for quantum-like (QL) probability laws, including interference effects, in non-quantum physical systems using coupled oscillators. In principle, such systems could produce QL states able to support QL computation in biological tissue. In this perspective, we propose a new avenue of research, namely to investigate if this is true in the human brain. Intriguingly, the special topology of human brain anatomy could promote the rich dynamical repertoire in human cognition. As a proof-of-principle, we investigated this by constructing two whole-brain models with and without QL dynamics, where the QL regime is distinguished by a larger whole-brain spectral gap. In accordance with our hypothesis, we found that the QL regime provides a significantly better fit to large-scale human empirical neuroimaging data and exhibits a lower model-derived energy cost than the non-QL model. Furthermore, we constructed a whole-brain model measuring the Växjö Interference term, a measure of functional quantum-like interference showing a significant correlation with the size of the spectral gap. Overall, these results suggest that quantum-like whole-brain models may provide a useful description of large-scale resting-state brain dynamics, and we set out what would be required to test whether this description also carries explanatory value for brain function.

Richard A. Mould

Javier Sánchez Cañizares

In recent decades, progress in the field of neurosciences has triggered an interest in understanding mind-brain relationships. Quantum Mechanics (QM) has been present in the debate from its beginnings through the well-known measurement paradox. The standard interpretation of QM considers two basic, fundamentally irreducible, processes: the deterministic evolution of the wave-function according to the Schrodinger equation, once the initial conditions have been settled; and the indeterministic wave-function collapse into one of the possible outcomes, after performing a specific measurement. So, QM would point to the limits of a purely deterministic view of nature and, in particular, of brains. Nevertheless, QM’s relevance for the brain’s physics is still to be proven. Detractors of the QM influence are confident of the role of decoherent processes at different physical scales in order to ensure a classical deterministic behavior of the brain. However, little attention is paid to the epistemic implications of invoking decoherence for the mind-brain problem. In this paper, (i) we present lasting QM models stating a specific view of human consciousness and make explicit their position regarding the relationship between the physical activity of neurons and/or networks of neurons and the phenomenal conscious experience; (ii) we review the main criticisms of the relevance of QM in the brain and, most importantly, we bring out the philosophical implications behind the usual recourse to decoherence in the transition from the quantum to the classical world, explaining why the mind-brain problem and the measurement paradox should not be disentangled.

H. Schmiedel

E. Linke

Luiz Pinguelli Rosa, Jean Faber

Quantum models of the mind associate consciousness with coherent superposition of states in the brain. Some authors consider consciousness to be the result of a kind of internal quantum measurement process in the brain. In this paper we discuss the ideas of Hameroff-Penrose and Tegmark and their calculation for an estimate of decoherence time. We criticize the Hameroff-Penrose model in the context of a quantum brain model by gravitational collapse orchestrated objective reduction (OOR), assumed by Penrose, and we propose instead that the decoherence process is caused by interaction with the environment. We consider it useful to exploit this possibility because of the growing importance of the decoherence theory in quantum measurement, and also because quantum mechanics can be applied to brain study independently of the Hameroff-Penrose model for mind and consciousness. Our conclusion is that the Hameroff-Penrose model is not compatible with decoherence, but nevertheless the quantum brain can still be considered if we replace gravitational collapse OOR with decoherence. However, our result does not agree with Tegmark's conclusion of refuting not only the Hameroff-Penrose gravitational collapse but also the quantum brain, based on decoherence time calculations in specific cases in the brain. In spite of this fact we also disagree with some points of the response to Tegmark's article given by Hagan, Hameroff, and Tuszynski.