In a compelling and at times disturbing series, Dr Michael Mosley explores the brutal history of experimental psychology. To begin, Michael traces the sinister ways this science has been used to try to control our minds. He finds that the pursuit of mind control has led to some truly horrific experiments and left many casualties in its wake. Extraordinary archive material captures what happened - scientists systematically change the behaviour of children, law-abiding citizens give fatal electric shocks and a gay man has electrodes implanted in his head in an attempt to turn his sexuality. Michael takes a hallucinogenic drug as part of a controlled experiment to try to understand how its mind-bending properties can change the brain. This is a scientific journey which goes to the very heart of what we hold most dear - our free will, and our ability to control our own destiny.

Dr Michael Mosley continues his exploration of the brutal history of experimental psychology. Experiments on the human mind have led to profound insights into how our brain works - but have also involved great cruelty and posed some terrible ethical dilemmas. In this film, Michael investigates how scientists have struggled to understand that most irrational and deeply complex part of our minds - our emotions. Michael meets survivors - both participants and scientists - of some of the key historical experiments. Many of these extraordinary research projects were captured on film - an eight-month-old boy is taught to fear random objects, baby monkeys are given mothers made from wire and cloth, and an adult is deliberately violent before a group of toddlers. Michael takes part in modern-day experiments to play his own small part in the quest to understand emotions.

Dr Michael Mosley concludes his series exploring the brutal history of experimental psychology by looking at how experiments on abnormal brains have revealed the workings of the normal brain. He meets remarkable individuals like Karen, who suffered from a rare condition - alien hand syndrome - which meant that one of her hands constantly attacked her. And Julia, who seems to have recovered from her stroke - until experiments reveal she is unable to recall the name of any object. Michael explores the case of an amnesiac known for years only by his initials, HM, who became the most studied individual in the history of psychology and whose extraordinary case opened a window on how our memory works. He visits the multi-million dollar centre which has been set up since HM died to map his unique brain down to the level of an individual neuron.