When you take risks, you are reminded in the most insistent manner that you have a body. For risk by its very nature threatens to hurt you. A driver speeding along a winding road, a surfer riding a monster wave as it crests over a coral reef, a mountain climber continuing his ascent despite an approaching blizzard, a soldier sprinting across no-man’s land – each of these people faces a high chance of injury, even death. And that very possibility sharpens the mind and calls forth an overwhelming biological reaction known as the ‘fight-or-flight’ response. In fact, so sensitive is your body to the taking of risk that you can be caught up in this visceral turmoil when death poses no immediate threat. Anyone who plays a sport or watches from the stands knows that even when it is ‘just a game’, risk engages our entire being. Winston Churchill, a hardened campaigner from the most deadly wars, recognised this power of non-lethal risk to grip us, body and mind. When writing of his early years, he tells of a regimental polo match played in southern India that went to a tie-break in the final chukka: ‘Rarely have I seen such strained faces on both sides,’ he recalls. ‘You would not have thought it was a game at all, but a matter of life and death. Far graver crises cause less keen emotion.’

It has been said of war that it consists of long stretches of boredom punctuated by brief periods of terror, and much the same can be said of trading. There are long stretches of time when little more than a trickle of business flows in through the sales desks, perhaps just enough to keep the restless traders occupied and to pay the bills. With no news of any importance coming across the wire, the market slows, the inertia feeding on itself until price movement grinds to a halt. Then, people on a trading floor disappear into their private lives: salespeople chat aimlessly with clients who have become friends, traders use the lull to pay bills, plan their next ski trip, or talk to headhunters, curious to know their value on the open market. Two traders, Logan, who trades mortgage-backed bonds, and Scott, who works down the aisle on the arbitrage desk, toss a tennis ball back and forth, taking care not to hit any salespeople.

In this book I tell the story of Scott and Logan, of Martin and Gwen, and of a trading floor of supporting characters, as they are caught in the floodtide of a bull and then a bear market. The story will consist of two threads: a description of overt trading behaviour – how professional traders make and lose money, the euphoria and stress that accompany their changing fortunes, the calculations behind bonus payments – and a description of the physiology behind the behaviour. The threads will, however, lace together, forming a single story. Splicing the two will enable us to see how brain and body act as one during important moments in a risk-taker’s life. We will explore pre-conscious circuits of the brain and their intimate links with the body in order to understand how people can react to market events so fast that their conscious brain cannot keep up, and how they draw on signals from the body, the fabled gut feelings, to optimise their risk-taking.