The Hour Between Dog and Wolf: Risk-taking, Gut Feelings and the Biology of Boom and Bust. John Coates
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widespread effects because they have receptors in almost every cell in our body and brain. Yet it was not until the 1990s that scientists began to understand just how these hormones influence our thinking and behaviour. Much of the work that led to this understanding was conducted in the lab of Bruce McEwen, a renowned professor at Rockefeller. He and his colleagues, including Donald Pfaff and Jay Weiss, were among the first scientists not only to map steroid receptors in the brain but also to study how steroids affect the structure of the brain and the way it works.
Before McEwen began his research, scientists widely believed that hormones and the brain worked in the following way: the hypothalamus, the region of the brain controlling hormones, sends a signal through the blood to the glands producing steroid hormones, be they testes, ovaries or adrenal glands, telling them to increase hormone production. The hormones are then injected into the blood, fan out across the body, and exert their intended effects on tissues such as heart, kidneys, lungs, muscles, etc. They also make their way back to the hypothalamus itself, which senses the higher hormone levels and in response tells the glands to stop producing the hormone. The feedback between hypothalamus and hormone-producing gland works much like a thermostat in a house, which senses cold and turns on the heating, and then senses the warmth and turns it off.
McEwen and his lab found something far more intriguing. Feedback between glands and the hypothalamus does indeed exist, is one of our most important homeostatic mechanisms, but McEwen discovered that there are steroid receptors in brain regions other than the hypothalamus. McEwen’s model of hormones and the brain works in the following way: the hypothalamus sends a message to a gland instructing it to produce a hormone; the hormone fans out across the body, having its physical effects, but it also returns to the brain, changing the very way we think and behave. Now, that is one potent chemical. Indeed, subsequent research by McEwen and others showed that a steroid hormone, because of its widespread receptors, can alter almost every function of our body (its growth, shape, metabolism, immune function) and of our brain (its mood and memory) and of our behaviour.
McEwen’s research was a landmark achievement because it showed how a signal from our body can change the very thoughts we think. And it raised a series of questions that today lie at the heart of our understanding of body and brain. Why does the brain send a signal to the body telling it to produce a chemical which in turn changes the way the brain works? What a strange thing to do. If the brain wants to change the way it thinks, why not keep all the signalling within the brain? Why take such a roundabout route through the body?
And why would a single molecule, like a steroid, be entrusted with such a broad mandate, simultaneously changing both body and brain? I think the answer to these questions goes something like this: steroid hormones evolved to coordinate body, brain and behaviour during archetypal situations, such as fighting, fleeing, feeding, hunting, mating and struggling for status. At important moments like these you need all your tissues cooperating on the task at hand; you do not want to be multi-tasking. It would make little sense to have, say, a cardiovascular system geared up for a fight, a digestive system primed for ingesting a turkey dinner, and a brain in the mood for wandering through fields of daffodils. Steroids, like a drill sergeant, ensure that body and brain fall into line as a single functioning unit.
The ancient Greeks believed that at archetypal moments in our lives we are visited by the gods, that we can feel their presence because these moments – of battle, of love, of childbearing – are especially vivid, are remembered as defining moments in our lives, and during them we seem to enjoy special powers. But alas, it is not one of the Olympian gods, poor creatures of abandoned belief that they are, who touches us at these moments: it is one of our hormones.
During moments of risk-taking, competition and triumph, of exuberance, there is one steroid in particular that makes its presence felt and guides our actions – testosterone. At Rockefeller University I came across a model of testosterone-fuelled behaviour that offered a tantalising explanation of trader behaviour during market bubbles, a model taken from animal behaviour called ‘the winner effect’.
In this model, two males enter a fight for turf or a contest for a mate and, in anticipation of the competition, experience a surge in testosterone, a chemical bracer that increases their blood’s capacity to carry oxygen and, in time, their lean-muscle mass. Testosterone also affects the brain, where it increases the animal’s confidence and appetite for risk. After the battle has been decided the winner emerges with even higher levels of testosterone, the loser with lower levels. The winner, if he proceeds to a next round of competition, does so with already elevated testosterone, and this androgenic priming gives him an edge, helping him win yet again. Scientists have replicated these experiments with athletes, and believe the testosterone feedback loop may explain winning and losing streaks in sports. However, at some point in this winning streak the elevated steroids begin to have the opposite effect on success and survival. Animals experiencing this upward spiral of testosterone and victory have been found after a while to start more fights and to spend more time out in the open, and as a result they suffer an increased mortality. As testosterone levels rise, confidence and risk-taking segue into overconfidence and reckless behaviour.
Could this upward surge of testosterone, cockiness and risky behaviour also occur in the financial markets? This model seemed to describe perfectly how traders behaved as the bull market of the nineties morphed into the tech bubble. When traders, most of whom are young males, make money, their testosterone levels rise, increasing their confidence and appetite for risk, until the extended winning streak of a bull market causes them to become every bit as delusional, overconfident and risk-seeking as those animals venturing into the open, oblivious to all danger. The winner effect seemed to me a plausible explanation for the chemical hit traders receive, one that exaggerates a bull market and turns it into a bubble. The role of testosterone could also explain why women seemed relatively unaffected by the bubble, for they have about 10 to 20 per cent of the testosterone levels of men.
During the dot.com bubble, when considering this possibility, I was particularly swayed by descriptions of the mood-enhancing effects of testosterone voiced by people who had been prescribed it. Patients with cancer, for example, are often given testosterone because, as an anabolic steroid – one that builds up energy stores such as muscle – it helps them put on weight. One brilliant and particularly influential description of its effects was written by Andrew Sullivan and published in the New York Times Magazine in April 2000. He vividly described injecting a golden, oily substance about three inches into his hip, every two weeks: ‘I can actually feel its power on almost a daily basis,’ he reported. ‘Within hours, and at most a day, I feel a deep surge of energy. It is less edgy than a double espresso, but just as powerful. My attention span shortens. In the two or three days after my shot, I find it harder to concentrate on writing and feel the need to exercise more. My wit is quicker, my mind faster, but my judgment is more impulsive. It is not unlike the kind of rush I get before talking in front of a large audience, or going on a first date, or getting on an airplane, but it suffuses me in a less abrupt and more consistent way. In a word, I feel braced. For what? It scarcely seems to matter.’ Sullivan could just as easily have been describing what it feels like to be a trader on a roll.
IRRATIONAL PESSIMISM
If testosterone seemed a likely candidate for the molecule of irrational exuberance, another steroid seemed a likely one for the molecule of irrational pessimism – cortisol.
Cortisol is the main hormone of the stress response, a bodywide response to injury or threat. Cortisol works in tandem with adrenalin, but while adrenalin is a fast-acting hormone, taking effect in seconds and having a half-life in the blood of only two to three minutes, cortisol kicks in to support us during a long siege. If you are hiking in the woods and hear a rustle in the bushes, you may suspect the presence of a grizzly bear, so the shot of adrenalin you receive is designed to carry you clear of danger. If the noise turns out to be nothing but wind in the leaves you settle down, and the adrenalin quickly dissipates. But if you are in fact being stalked by a predator and the chase lasts several hours, then cortisol takes over the management of your body. It orders all long-term and metabolically expensive functions of the body, such as digestion, reproduction, growth, storage of energy, and after a while even immune function, to stop. At the same time, it begins to break down energy stores and flush the liberated glucose into your blood. In short, cortisol has