In this ground-breaking tour of the human mind, a world-renowned psychiatrist and neuroscientist explores the origins of human emotion through the stories of his patients. Why do we feel what we feel? How do we define 'sanity'? Can a lost mind be found again? Since the dawn of humankind, mental illness has been one of our greatest causes of suffering as a species. But for the majority of our history, its causes have remained a mystery. Now, science has reached a tipping point. In 'Connections', Professor Karl Deisseroth shares his breakthrough discovery, Optogenetics, a biological technique that allows us to decipher the brain's inner workings using light.