  In the early 1970s Thomas Nagel argued in “What Is It Like to Be a Bat?” (1974) that consciousness itself—especially the subjective character of what it is like to have a certain type of experience—escapes physical theory. Many philosophers pressed the case that sensory qualia—what it is like to feel pain, to see red, etc.—are not addressed or explained by a physical account of either brain structure or brain function. Consciousness has properties of its own. And yet, we know, it is closely tied to the brain. And, at some level of description, neural activities implement computation.