 When he wrote his first consciousness book, "The Emperor's New Mind" in 1989, Penrose lacked a detailed proposal for how such quantum processes could be implemented in the brain.Subsequently, Stuart Hameroff read "The Emperor's New Mind" and suggested to Penrose that certain structures within brain cells (microtubules) were suitable candidate sites for quantum processing and ultimately for consciousness.The Orch-OR theory arose from the co-operation of these two scientists and was developed in Penrose's second consciousness book "Shadows of the Mind" (1994).