Quantum computation in brain microtubules: decoherence and biological feasibility

Area of Science:

• Neuroscience
• Quantum Biology
• Biophysics

Background:

• The Penrose-Hameroff orchestrated objective reduction (orch. OR) model proposes quantum computations in brain microtubules are linked to consciousness.
• Previous criticisms, notably by Tegmark, suggested microtubules decohere too rapidly for neurophysiological relevance (10^-13 s).

Purpose of the Study:

• To critically examine decoherence mechanisms in microtubules within a biological context.
• To re-evaluate the timescale of quantum coherence in microtubules relevant to the orch. OR model.

Main Methods:

• Re-calculation of decoherence times based on the specific parameters of the orch. OR model, correcting for discrepancies in Tegmark's analysis.
• Analysis of biological factors influencing decoherence, including metabolic energy, counterion screening, and actin gel effects.
• Consideration of topological quantum computation for error correction.

Main Results:

• Corrected decoherence times are significantly longer (10^-5–10^-4 s), challenging Tegmark's conclusions.
• Biological factors like metabolic energy and microtubule-associated structures can actively counter decoherence.
• Tegmark's model shows counterintuitive temperature dependence and inappropriate approximation regimes for orch. OR.

Conclusions:

• Microtubule decoherence times are potentially long enough for neurophysiological relevance.
• The orch. OR model's quantum computations may be shielded from environmental decoherence by biological mechanisms.
• Quantum gravity interactions with neurophysiology are plausible within the revised decoherence framework.