How does our mind, our individual sense of self, emerge from the physical matter of the brain? Inside our heads, 86 billion neurons communicate with one another through very precise connections, but when this is disrupted, it can result in autism, depression, schizophrenia, PTSD, and addictions. While these issues bring great suffering, Nobel Prize winner Eric Kandel points out, they can also reveal how the brain produces our most fundamental experiences and capabilities—the very nature of what it means to be human. Drawing on case studies and a lifetime of research, Kandel grapples with the big question of how billions of neurons generate consciousness itself.