Volatile anesthetics like isoflurane may cause unconsciousness by binding to microtubules (MTs) inside neurons and dampening their quantum optical effects. In male rats injected with the MT-stabilizing drug epothilone B (epoB), loss of righting reflex under 4% isoflurane took an average of 69 seconds longer than in rats given a placebo. The difference was statistically significant with a large effect size (Cohen's d = 1.9) and could not be explained by tolerance from repeated anesthetic exposure. This supports the idea that consciousness arises from quantum physical states in neural microtubules, as proposed in the orchestrated objective reduction (Orch OR) theory.
Recent experimental evidence indicates that inhalational anesthetics target intraneuronal microtubules, supporting the hypothesis that consciousness arises from a collective quantum state of microtubules, as predicted by the Orchestrated Objective Reduction theory. Evidence also shows functionally relevant quantum effects in microtubules at room temperature and a macroscopic quantum entangled state in the living human brain correlated with conscious state and working memory. The quantum model makes panprotopsychism a viable solution to the hard problem by solving the binding problem, but raises an epiphenomenalism problem. The author proposes the quantum approach can solve this, and the Orch OR theory accounts for nonalgorithmic understanding and the psychological arrow of time.