In this riveting journey through the hidden realms of the human mind, a world-renowned psychiatrist and neuroscientist explores the origins of human emotion, and examines what mental illnesses reveal about all of us - how the broken can illuminate the unbroken.

Why do we feel what we feel?

Mental illness is one of the greatest causes of human suffering, but the reasons we bear this burden, and the nature of these diseases, have remained mysterious. Now, our understanding has reached a tipping point. In Connections, Professor Karl Deisseroth intertwines gripping case studies from his experience as an emergency psychiatry physician, with breakthrough scientific discoveries from astounding new technology (including optogenetics, which he developed to allow turning specific brain cells on or off, with light).

By linking insights from this technology to deeply moving stories of his patients and to our shared evolutionary history, Deisseroth tells a larger story about the origins of human emotion. A young woman with an eating disorder reveals how the mind can rebel against the brain's most primitive drives of hunger and thirst; an older man, smothered into silence by dementia, shows how humans evolved to feel joy and its absence; and a lonely Uyghur woman far from her homeland teaches both the importance - and challenges - of deep social bonds.