Consciousness poses a puzzle: unified experience arises from distributed brain activity. Classical neuroscience explains synaptic and network mechanisms, but debates continue over whether quantum principles are needed. This review examines quantum ideas in two ways: as mathematical models for context-dependent cognition and as hypotheses about real quantum states in the brain. It surveys evidence from MRI signals, learning models, and proposed neural substrates like microtubules and nuclear spins. No study has yet demonstrated entanglement or long-lived coherence in neural tissue under standard quantum criteria. Replication is limited, and classical dynamics can mimic quantum signatures. The key question is whether brain dynamics exceed classical models. Progress requires precise tests to distinguish quantum correlations from classical complexity.
Consciousness presents a structural puzzle: a unified, context-sensitive, globally integrated mode of experience emerging from distributed neural dynamics. This review examines whether quantum principles offer explanatory leverage as formal mathematical frameworks for modeling contextual cognition and as mechanistic hypotheses proposing biologically instantiated non-classical states. It surveys empirical and theoretical developments spanning zero-quantum-coherence in MRI signals, entanglement-structured learning paradigms, quantum-inspired computational models, and proposed neural substrates including microtubules, nuclear spins, and photonic architectures. Although certain findings have been interpreted as consistent with a non-classical structure, no study to date has demonstrated entanglement, long-lived coherence, or collapse dynamics in neural tissue under operational criteria comparable to those used in controlled quantum systems. The decisive question is whether brain dynamics exceed the explanatory reach of rigorously defined classical models.