With 86 billion nerve cells joined together in a network of 100 trillion connections, the human brain is the most complex system in the known universe. Dr. Hannah Critchlow is an internationally acclaimed neuroscientist who has spent her career demystifying and explaining the brain to audiences around the world. Through her writing, broadcasting and lectures to audiences – whether in schools, festivals or online – she has become one of the public faces of neuroscience. She tells Professor Jim Al-Khalili that her desire to understand the brain began when she spent a year after school as a nursing assistant in a psychiatric hospital. The experience of working with young patients - many the same age as her - made her ask what it is within each individual brain which determines people’s very different life trajectories. In her books she’s explored the idea that much of our character and behaviour is hard-wired into us before we’re even born. And most recently she’s considered collective intelligence, asking how we can bring all our individual brains together and harness their power in one ‘super brain’. And we get to hear Jim’s own mind at work as Hannah attaches electrodes to his head and turns his brain waves into sound. Producer: Jeremy Grange