IF THE losses at UBS that surfaced this month were caused by a “rogue” trader, would that make his colleagues stable? Not if research being undertaken by John Coates, a neuroscientist at Cambridge University and a former derivatives trader, is anything to go by. His work suggests that hormones drive investment decisions to a far greater extent than economists or bank executives realise. When traders are on a winning streak, their testosterone levels surge, sparking such euphoria that they underestimate risk. When they are acutely stressed, the adrenal cortex produces a flood of cortisol, a hormone that can make them overly fearful and risk-averse.