The hypothesis proposes that quantum entanglement between microtubule subunits inside neurons could provide a physical substrate for unified subjective experience, attempting to bridge the explanatory gap between objective neural activity and first-person consciousness. Proponents (notably Penrose and Hameroff) frame this as the Orchestrated Objective Reduction model, while critics argue that the brain's warm, wet environment causes decoherence on time-scales far too short for cognition-relevant computation. No experiment to date has produced reproducible evidence of brain-scale quantum coherence. The proposal is currently speculative and treated as a working hypothesis rather than established theory.