Combatting the dark thoughts in our brains

What's going on in our brains when we experience dark or negative thoughts, and how can we combat them? Lance Burdett spent 22 years in the police, and was the National Advisor for all police negotiation teams. His time as a crisis negotiator saw him deal with a range of volatile situations. used his personal experience with depression, and the loss of his teenage niece to suicide, in a new book that tries to explains what's going on in our brains when we're anxious, stressed, depressed and suicidal. He joins Kathryn to talk about Dark Side of the Brain: Adapting to Adversity.