Potential features of quantum computation could explain enigmatic aspects of consciousness. The Penrose—Hameroff model (orchestrated objective reduction: ‘Orch OR’) suggests that quantum superposition and a form of quantum computation occur in microtubules—cylindrical protein lattices of the cell cytoskeleton within the brain's neurons. Microtubules couple to and regulate neural–level synaptic functions, and they may be ideal quantum computers because of dynamical lattice structure, quantum–level subunit states and intermittent isolation from environmental interactions. In addition to its biological setting, the Orch OR proposal differs in an essential way from technologically envisioned quantum computers in which collapse, or reduction to classical output states, is caused by environmental decoherence (hence introducing randomness). In the Orch OR proposal, reduction of microtubule quantum superposition to classical output states occurs by an objective factor: Roger Penrose's quantum gravity threshold stemming from instability in Planck–scale separations (superpositions) in spacetime geometry. Output states following Penrose's objective reduction are neither totally deterministic nor random, but influenced by a non–computable factor ingrained in fundamental spacetime. Taking a modern pan–psychist view in which protoconscious experience and Platonic values are embedded in Planck–scale spin networks, the Orch OR model portrays consciousness as brain activities linked to fundamental ripples in spacetime geometry.