What microtubules are

Microtubules are hollow tubes about 25 nanometres wide, assembled from two closely related proteins, α- and β-tubulin. They grow and shrink constantly, give cells their shape, separate chromosomes when cells divide, and serve as tracks along which motor proteins carry cargo. In neurons they run the length of axons and dendrites and are vital to transport and to the structure of synapses.

Why were they linked to consciousness?

Two lines of reasoning converged in the 1990s. Roger Penrose was looking for a place in the brain where quantum effects could matter; Stuart Hameroff, from anaesthesiology, suspected that the molecular target of anaesthesia lay inside neurons rather than only at their membranes. The regular, lattice-like structure of microtubules made them an appealing candidate for coordinated quantum states. This is the biological half of Orch OR.

Anaesthesia and microtubules

General anaesthetics remove consciousness reversibly, which makes them a powerful tool for consciousness research. The classic view is that they act mostly on receptors and ion channels in neuron membranes, and that remains well supported. Some studies have also reported that anaesthetics bind to tubulin or alter microtubule dynamics, and a 2024 rat study reported that a drug stabilising microtubules delayed the loss of righting reflex (a standard proxy for unconsciousness) under isoflurane. These results are interesting but do not show that microtubules are the main site of action, nor that any effect is quantum in nature.

Quantum biology precedents

It used to be assumed that living tissue is too warm and noisy for quantum effects. That assumption has softened: quantum tunnelling is important in some enzyme reactions, and a quantum “radical pair” mechanism is the leading explanation of how some birds sense magnetic fields. Laboratory studies have also reported unusual collective light-energy transfer in tubulin and microtubule preparations. None of this shows that quantum states in microtubules are linked to experience, but it keeps the question open.

What lab results can and cannot show

Most measurements are made on purified proteins or cells in a dish, not in a functioning brain. Effects seen at low temperatures or in isolated preparations may not survive in living tissue. And a correlation between microtubule changes and loss of consciousness could arise because microtubules support ordinary neural signalling, not because they generate experience.

Open questions

• Can coherent quantum states survive in microtubules in living neurons long enough to affect firing?
• Do anaesthetics act on microtubules at clinically relevant doses in humans?
• Would disrupting microtubule quantum effects, without disrupting ordinary function, change consciousness?

Health note: this article discusses basic research. It does not concern diagnosis or treatment of any disease and is not medical advice.