Quantum effects in the brain: A review

This review examines theories proposing that quantum effects contribute to neural processing and consciousness. It describes how the initial microtubule hypothesis from the mid-1990s was dismissed because quantum effects seemed unlikely in warm, wet biological systems, but developments in quantum biology—showing quantum effects in photosynthesis, avian migration, and olfaction—have revived interest. The review covers proposals that general anaesthetics act through quantum means via electron spin changes, that the tunnelling hypothesis from olfaction applies to neurotransmitters, and that phosphorus nuclear entanglement might influence neuron firing. It assesses the experimental evidence supporting these theories and clarifies the proposed biological sites of quantum effects in the brain.

Study at a glance

Abstract

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 anaesthetic, which switches off consciousness, does this through quantum means, measured by changes in electron spin. The tunnelling 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.