Book excerpt: Here, leading neuroscientist Nancy Andreasen offers a state-of-the-art look at what we know about the human brain and the human genome--and shows how these two vast branches of knowledge are coming together in a boldly ambitious effort to conquer mental illness. Andreasen gives us an engaging and readable description of how it all works---from billions of neurons, to the tiny thalamus, to the moral monitor in our prefrontal cortex. She shows the progress made in mapping the human genome, whose 30,000 to 40,000 genes are almost all active in the brain. We read gripping stories of the people who develop mental illness, the friends and relatives who share their suffering, the physicians who treat them, and the scientists who study them so that better treatments can be found. Four major disorders are covered--schizophrenia, manic depression, anxiety disorders, and dementia--revealing what causes them and how they affect the mind and brain. Finally, the book shows how the powerful tools of genetics and neuroscience will be combined during the next decades to build healthier brains and minds. By revealing how combining genome mapping with brain mapping can unlock the mysteries of mental illness, Andreasen offers a remarkably fresh perspective on these devastating diseases.