Four renowned brain scientists tackle the conundrum of how to define, let alone study, consciousness. Their differences are immediately apparent as they attempt to describe consciousness and determine why it should include our sensory inputs, our experiences and our inner lives. They discuss the concept of “zombies” -- where a mythical patient being is capable of performing certain tasks while remaining unaware of the surrounding environment – as one pathway to understanding. They all agree that other productive areas of study focus on how exactly the brain reacts to anesthesia or how it enables the process of making choices. The episode concludes with a lively exchange of ideas about the relevance of measuring nerve cell activity, the possible role of quantum mechanics in consciousness, and the capacity of molecular biology to aid the brain. With Joseph Bogen, Leslie Brothers, Stuart Hameroff, Christof Koch.