The Hour Between Dog and Wolf: Risk-taking, Gut Feelings and the Biology of Boom and Bust

Logan stops in mid-throw and looks over his shoulder at the screens. Scott has already wheeled his chair back to his desk. Their monitors display thousands of prices and flowing news feeds, blinking and disappearing. To outsiders the vast matrix of numbers seems chaotic, overwhelming, and finding the significant bit of information in the mess of prices and irrelevant news items seems as impossible as picking out a single star in the Milky Way. But a good trader can do just that. Call it a hunch, call it gut feeling, call it tradecraft, but this morning Scott and Logan have sensed a kaleidoscopic shift in price patterns well before they can say why.

One of the brain regions responsible for this early-warning system is the locus ceruleus (pronounced ser-u-leus), so called because its cells are cerulean, or deep blue. Situated in the brain stem, the most primitive part of the brain, sitting atop the spine, the locus ceruleus responds to novelty and promotes a state of arousal. When a correlation between events breaks down or a new pattern emerges, when something is just not right, this primitive part of the brain registers the change long before conscious awareness. By doing so it places the brain on high alert, galvanising us into a state of heightened vigilance, and lowering our sensory thresholds so that we hear the faintest sound, notice the slightest movement. Athletes experiencing this effect have said that when caught up in the flow of a game they can pick out every voice in the stadium, see every blade of grass. And today when the stable correlations between asset prices broke down the locus ceruleus tripped an alarm, causing Scott and Logan to orient to the disturbing information.

Moments after Scott and Logan have pre-consciously registered the change, they learn that one or two people on the Street have heard, or suspected, that the Fed will raise interest rates this afternoon. Such a decision announced to an unprepared financial community would send a tidal wave of volatility through the markets. As the news and its implications sink in, Wall Street, only a short while ago looking forward to calling it an early day, roils with activity. At hastily organised meetings traders consider the possible Fed moves – will it leave rates unchanged? Raise them a quarter of a percentage point? Half a per cent? What will bonds do under each scenario? What will stocks do? Having formed their views, traders then jostle to set their positions, some selling bonds in anticipation of a rate hike, which pushes the market down almost 2 per cent, others buying them at the new lower levels, convinced the market is oversold.

Markets feed on information, and the Fed announcement will be a feast. It will bring volatility to the market, and volatility to a trader means a chance to make money. So this afternoon most traders exude excitement, and many of them will make their entire week’s profit in the next few hours. Around the world bankers stay up to hear the news, and trading floors now buzz with a ludic atmosphere more commonly found at a fair or sporting event. Logan warms to the challenge and with a rebel yell dives into the seething market, selling $200 million of mortgage bonds, anticipating an exciting ride down.

By 2.10, trading on the screen dwindles. The floor goes quiet. Across the world traders have placed their bets, and now wait. Scott and Logan have readied their positions and feel intellectually prepared. But the challenge they face is more than an intellectual puzzle. It is also a physical task, and to perform it successfully they require a lot more than cognitive skills. They also need fast reactions, and stamina enough to support their efforts for the hours ahead when volatility spikes. What their bodies need, therefore, is fuel, lots of it, in the form of glucose, and they need oxygen to burn this fuel, and they need an increased flow of blood to deliver this fuel and oxygen to gas-guzzling cells throughout the body, and they need an expanded exhaust pipe, in the form of dilated bronchial tubes and throat, to vent the carbon dioxide waste once the fuel is burned.

Consequently Scott and Logan’s bodies, largely unbeknownst to them, have also prepared for the event. Their metabolism speeds up, ready to break down existing energy stores in liver, muscle and fat cells should the situation demand it. Breathing accelerates, drawing in more oxygen, and their heart rates speed up. Cells of the immune system take up position, like firefighters, at vulnerable points of their bodies, such as the skin, and stand ready to deal with injury and infection. And their nervous system, extending from the brain down into the abdomen, has begun redistributing blood throughout their bodies, constricting blood flow to the gut, giving them the butterflies, and to the reproductive organs – since this is no time for sex – and shunting it to major muscle groups in the arms and thighs as well as to the lungs, heart and brain.

As the sheer potential for profit looms in their imaginations, Scott and Logan feel an unmistakable surge of energy as steroid hormones begin to turbo-charge the big engines of their bodies. These hormones take time to kick in, but once synthesised by their respective glands and injected into the bloodstream, they begin to change almost every detail of Scott and Logan’s body and brain – their metabolism, growth rate, lean-muscle mass, mood, cognitive performance, even the memories they recall. Steroids are powerful, dangerous chemicals, and for that reason their use is tightly regulated by law, by the medical profession, by the International Olympic Committee, and by the hypothalamus, the brain’s ‘drug enforcement agency’; for if steroid production is not turned off quickly it can transform us, body and mind.

From the moment the rumour first spread, and over the past couple of hours, Scott and Logan’s testosterone levels have been steadily climbing. This steroid hormone, naturally produced by the testes, primes them for the challenge ahead, just as it does athletes preparing to compete and animals steeling for a fight. Rising levels of testosterone increase Scott and Logan’s haemoglobin, and consequently their blood’s capacity to carry oxygen; the testosterone also increases their state of confidence and, crucially, their appetite for risk. For Scott and Logan, this is a moment of transformation, what the French since the Middle Ages have called ‘the hour between dog and wolf’.

Another hormone, adrenalin, produced by the core of the adrenal glands located on top of the kidneys, surges into their blood. Adrenalin quickens physical reactions and speeds up the body’s metabolism, tapping into glucose deposits, mostly in the liver, and flushing them into the blood so that Scott and Logan have back-up fuel supplies to support them in whatever trouble their testosterone gets them into. A third hormone, the steroid cortisol, commonly known as the stress hormone, trickles out of the rim of the adrenal glands and travels to the brain, where it stimulates the release of dopamine, a chemical operating along neural circuits known as the pleasure pathways. Normally stress is a nasty experience, but not at low levels. At low levels it thrills. A non-threatening stressor or challenge, like a sporting match, a fast drive or an exciting market, releases cortisol, and in combination with dopamine, one of the most addictive drugs known to the human brain, it delivers a narcotic hit, a rush, a flow that convinces traders there is no other job in the world.

Now, at 2.14, Scott and Logan lean into their screens, gaze steady, pupils dilated; heart rates drop to a slow idle; their breathing rhythmic and deep; muscles coiled; body and brain fused for the impending action. An expectant hush descends on global markets.

THE INSIDE STORY

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.

Despite the traders’ frequent successes, the story follows the narrative arc of tragedy, with its grim and unstoppable logic of overconfidence and downfall, what the ancient Greeks called hubris and nemesis. For human biology obeys seasons of its own, and as traders make and lose money they are led almost irresistibly into recurrent cycles of euphoria, excessive risk-taking and crash. This dangerous pattern repeats itself in the financial markets every few years. Alan Greenspan, former chairman of the US Federal Reserve, puzzled over this periodic folly, and wrote of ‘innate human responses that result in swings between euphoria and fear that repeat themselves generation after generation’. Much the same pattern occurs in sport, politics and war, where larger-than-life characters, believing themselves exempt from the laws of nature and morality, overreach their abilities. Extraordinary success seems inevitably to breed excess.

Why is this? Recent research in physiology and neuroscience can, I believe, help us explain this ancient, delusional and tragic behaviour. Human biology can today help us understand overconfidence and irrational exuberance, and it can contribute to a more scientific understanding of financial market instability.

A simpler reason for bringing biology into the story is that it is, quite simply, fascinating. A story of human behaviour spiked with biology can lead to particularly vivid moments of recognition. The term ‘recognition’ is commonly used to describe the point in a story when all of a sudden we understand what is going on, and by that very process understand ourselves. It was Aristotle who coined this term, and since his day recognition moments have been largely the preserve of philosophy and literature. But today they are increasingly provided, for me at any rate, by human biology. For when we understand what is going on inside our bodies, and why, we are met with repeated Aha! moments. These range from the fun: ‘Oh, so that’s why I get butterflies in my stomach when excited!’ or ‘So that’s why I get goosebumps when scared!’ (The erector pili muscles in your skin try to raise your fur, to make you look bigger, just as a cat does when threatened. Most of your fur no longer exists, so you get goosebumps instead, but where it does you have a ‘hair-raising’ experience) – to the deadly serious: ‘So that’s why stress is so tormenting, why it contributes to gastric ulcers, hypertension, even heart disease and stroke!’

Today human biology, perhaps more than any other subject, throws a light into the dark corners of our lives. So by mixing biology into the story I can more accurately describe what it feels like to take large financial risks; and I can do so moreover in a way that provides recognition moments for people who have never set foot on a trading floor. In fact, the physiology I describe is not confined to traders at all. It is the universal biology of risk-taking. As such it has been experienced by anyone who plays a sport, runs for political office, or fights in a war. But I focus on financial risk-taking, and do so for good reason: first, because finance is a world I know, having spent twelve years on Wall Street; second, and more importantly, because finance is the nerve centre of the world economy. If athletes succumb to overconfidence, they lose a match, but if traders get carried away on a flood of hormones, global markets founder. The financial system, as we have recently discovered to our dismay, balances precariously on the mental health of these risk-takers.

I begin by looking at the physiology that produces our risk-taking, filling in the background story for what follows. I then show, through a story set on a trading floor, how this physiology can mix with lax risk-management systems and a bonus system that rewards excessive gambling to produce a volatile and explosive bank. We watch as nature and nurture conspire to produce an awful train wreck, leaving behind mangled careers, damaged bodies and a devastated financial system. We then linger in the wreckage and observe the resulting fatigue and chronic stress, two medical conditions that blight the workplace. Finally we look at some tentative yet hopeful research into the physiology of toughness, in other words training regimes designed by sports scientists and stress physiologists to immunise our bodies against an overactive stress response. Such training could help calm the unstable physiology of risk-takers.

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THE FEELING OF A BUBBLE

My interest in the biological side of the financial markets dates back to the 1990s. I was then working on Wall Street, trading derivatives for Goldman Sachs, then Merrill Lynch, and finally running a desk for Deutsche Bank. This was a fascinating time to trade the markets, because New York, and indeed America as a whole, was caught up in the dot.com bubble. And what a bubble that was. The markets had not seen anything quite like it since the great bull market of the 1920s. In 1991 the Nasdaq (the electronic stock exchange where many new-tech ventures are listed) traded below 600, and had meandered around that level for a few years. It then began a gradual yet persistent bull run, reaching a level of 2,000 in 1998. The Nasdaq’s rise was checked for a year or so by the Asian Financial Crisis, which reined it back about 500 points, but then the market recovered and took to the skies. In little more than a year and a half the Nasdaq shot up from 1,500 to a peak just over 5,000, for a total return in excess of 300 per cent.

The rally was almost unprecedented in its speed and magnitude. It was completely unprecedented in the paucity of hard financial data supporting the dot.com and high-tech ventures powering the bull run. In fact, so large was the gap between stock prices and the underlying fundamentals that many legendary investors, betting unsuccessfully against the trend, retired from Wall Street in disgust. Julian Robertson, for instance, founder of the hedge fund Tiger Capital, threw in the towel, saying in effect that the market may have gone crazy but he had not. Robertson and others were right that the market was due for a dreadful day of reckoning, but they also fully understood a point made by the great economist John Maynard Keynes back in the 1930s: that the markets could remain irrational longer than they, the investors, could remain solvent. So Robertson retired from the field, his reputation and capital largely intact. Then, early in 2000, the Nasdaq collapsed, giving back over 3,000 points in little more than a year, eventually bottoming out at the 1,000 level where it had begun a few short years before. Volatility of this magnitude normally makes a few people rich, but I know of no one who made money calling the top of this market’s explosive trajectory.

Besides the scale of the run-up and subsequent crash, another feature of the Bubble was noteworthy, and reminiscent of the 1920s, at least the 1920s I knew from novels, black-and-white movies and grainy documentaries – that was how its energy and excitement overflowed the stock exchange, permeated the culture and intoxicated people. For the fact is, while they last, bubbles are fun; and the widespread silliness attending them is often remembered with a certain amount of humour and fondness. I imagine anyone who lived through the bull market of the Roaring Twenties retained an abiding nostalgia for that heroic and madcap time, when futuristic technology, blithe spirits and easy wealth seemed to herald a new era of boundless possibility. Of course, life in its aftermath must have been even more formative, and those born and raised during the Great Depression are said to carry, even into old age, what the historian Caroline Bird calls an ‘invisible scar’, a pathological distrust of banks and stock markets, and a morbid fear of unemployment.

My recollections of the 1990s are of a decade every bit as hopeful and every bit as screwball as the 1920s. During the nineties we were entertained by middle-aged CEOs in black poloneck sweaters trying to ‘think outside the box’; by kids in their twenties wearing toques and yellow sunglasses, backed by apparently limitless amounts of capital, throwing lavish parties in midtown lofts and talking wacky internet schemes few of us could understand – and even fewer questioned. To do so meant you ‘just didn’t get it’, one of the worst insults of the time, indicating that you were a dinosaur incapable of lateral thought. One thing I definitely didn’t get was how the internet was supposed to overcome the constraints of time and space. Sure, ordering online was easy, but then delivery took place in the real world of rising oil prices and road congestion. The internet company that made the most heroic attempt to defy this brute fact was Kozmo.com, a New York-based start-up that promised free delivery within Manhattan and about a dozen other cities within an hour. The people who paid the price for this act of folly, besides the investors, were the scores of bicycle messengers breathlessly running red lights to meet a deadline. You would see groups of these haggard youngsters outside coffee bars (with appropriate names like Jet Fuel) catching their breath. Not surprisingly the company went bankrupt, leaving behind a question asked about this and countless similar ventures: what on earth were the investors thinking?

Perhaps the right question should have been, were they thinking at all? Were investors engaged in a rational assessment of information, as many economists might – and did – argue? If not, then were they perhaps engaged in a different form of reasoning, something closer to a game theoretic calculation: ‘I know this thing is a bubble,’ they may have schemed, ‘but I’ll buy on the way up and then sell before everyone else.’ Yet when talking to people who were investing their savings in newly listed internet shares I found little evidence for either of these thought processes. Most investors I spoke to had difficulty employing anything like linear and disciplined reasoning, the excitement and boundless potential of the markets apparently being enough to validate their harebrained ideas. It was almost impossible to engage them in a reasoned discussion: history was irrelevant, statistics counted for little, and when pressed they shot off starbursts of trendy concepts like ‘convergence’, the exact meaning of which I never discerned, although I think it had something to do with everything in the world becoming the same – TVs turning into phones, cars into offices, Greek bonds yielding the same as German, and so on.

If investors who had bought into this runaway market displayed little of the thought processes described by either rational choice or game theory, they also displayed little of the behaviour implied by a more common and clichéd account – the fear and greed account of investor folly. According to this piece of folk wisdom a bull market, as it picks up steam, churns out extraordinary profits, and these cause the better judgement of investors to become warped by the distemper of greed. The implication is that investors know full well that the market is a bubble, yet greed, rather than cunning, causes them to linger before selling.

Greed certainly can and does cause investors to run with their profits too long. By itself, though, the account misses something important about bubbles like the dot.com era and perhaps the Roaring Twenties – that investors naïvely and fervently believe they are buying into the future. Cynicism and cunning are not on display. Furthermore, as a bull market starts to validate investors’ beliefs, the profits they make translate into a lot more than mere greed: they bring on powerful feelings of euphoria and omnipotence. It is at this point that traders and investors feel the bonds of terrestrial life slip from their shoulders and they begin to flex their muscles like a newborn superhero. Assessment of risk is replaced by judgements of certainty – they just know what is going to happen: extreme sports seem like child’s play, sex becomes a competitive activity. They even walk differently: more erect, more purposeful, their very bearing carrying a hint of danger: ‘Don’t mess with me,’ their bodies seem to say. ‘I can handle anything.’ Tom Wolfe nailed this delusional behaviour when he described the stars of Wall Street as ‘Masters of the Universe’.

It was this behaviour more than anything else that struck me during the dot.com era. For the undeniable fact was, people were changing. The change showed itself not only among the untrained public but also, perhaps even more, among professional traders all along Wall Street. Normally a sober and prudent lot, these traders were becoming by small steps euphoric and delusional. Their minds were frequently troubled by racing thoughts, and their personal habits were changing: they were making do with less sleep – clubbing till 4 a.m. – and seemed to be horny all the time, more than usual at any rate, judging by their lewd comments and the increased amount of porn on their computer screens. More troubling still, they were becoming overconfident in their risk-taking, placing bets of ever-increasing size and with ever worsening risk–reward trade-offs. I was later to learn that the behaviour I was witnessing showed all the symptoms of a clinical condition known as mania (but now I am getting ahead of the story).

These symptoms are not unique to Wall Street: other worlds also manifest them, politics for example. One particularly insightful account of political mania has been provided by David Owen, now Lord Owen. Owen, a former Foreign Secretary and one of the founders of the Social Democratic Party, has spent most of his life at the very top of British politics. But he is by training a neurologist, and has lately taken to writing about a personality disorder he has observed among political and business leaders, a disorder he calls the Hubris Syndrome. This syndrome is characterised by recklessness, an inattention to detail, overwhelming self-confidence and contempt for others; all of which, he observes, ‘can result in disastrous leadership and cause damage on a large scale’. The syndrome, he continues, ‘is a disorder of the possession of power, particularly power which has been associated with overwhelming success, held for a period of years and with minimal constraint on the leader’. The symptoms Owen describes sound strikingly similar to those I observed on Wall Street, and his account further suggests an important point – that the manic behaviour displayed by many traders when on a winning streak comes from more than their newly acquired wealth. It comes equally, perhaps more, from a feeling of consummate power.

During the dot.com years I was in a good position to observe this manic behaviour among traders. On the one hand I was immune to the siren call of both Silicon Valley and Silicon Alley. I never had a deep understanding of high tech, so I did not invest in it, and could watch the comedy with a sceptical eye. On the other, I understood the traders’ feelings because I had in previous years been completely caught up in one or two bull markets myself, ones you probably did not hear about unless you read the financial pages, as they were isolated in either the bond or the currency market. And during these periods I too enjoyed above-average profits, felt euphoria and a sense of omnipotence, and became the picture of cockiness. Frankly, I cringe when I think about it.

So during the dot.com bubble I knew what the traders were going through. And the point I want to make is this: the overconfidence and hubris that traders experience during a bubble or a winning streak just does not feel as if it is driven by a rational assessment of opportunities, nor by greed – it feels as if it is driven by a chemical.

When traders enjoy an extended winning streak they experience a high that is powerfully narcotic. This feeling, as overwhelming as passionate desire or wall-banging anger, is very difficult to control. Any trader knows the feeling, and we all fear its consequences. Under its influence we tend to feel invincible, and to put on such stupid trades, in such large size, that we end up losing more money on them than we made on the winning streak that kindled this feeling of omnipotence in the first place. It has to be understood that traders on a roll are traders under the influence of a drug that has the power to transform them into different people.

Perhaps this chemical, whatever it is, accounts for much of the silliness and extreme behaviour that accompany bubbles, making them unfold much like a midsummer night’s dream, with people losing themselves in ill-fated delusions, mixed identities and swapped partners, until the cold light of dawn brings the world back into focus and the laws of nature and morality reassert themselves. After the dot.com bubble burst, traders were like revellers with a hangover, heads cradled in hands, stunned that they could have blown their savings on such ridiculous schemes. The shocked disbelief that the reality sustaining them for so long had turned out to be an illusion has nowhere been better described than on the front page of the New York Times the day after the Great Crash of 1929: ‘Wall St.,’ it reported, ‘was a street of vanished hopes, of curiously silent apprehension and a sort of paralyzed hypnosis.’

IS THERE AN IRRATIONAL EXUBERANCE MOLECULE?

As I say, the overconfident behaviour I describe is one that most traders will recognise and most have experienced at one point or another in their careers. I should add, however, that in addition to the changed behaviour among traders, another remarkable fact struck me during the dot.com years – that women were relatively immune to the frenzy surrounding internet and high-tech stocks. In fact, most of the women I knew, both on Wall Street and off, were quite cynical about the excitement, and as a result were often dismissed as ‘not getting it’, or worse, resented as perennial killjoys.

I have a special reason for relating these stories of Wall Street excess. I am not presenting them as items of front-line reportage, but rather as overlooked pieces of scientific data. Scientific research often begins with fieldwork. Fieldwork turns up curious phenomena or observations that prove to be anomalies for existing theory. The behaviour I am describing constitutes precisely this sort of field data for economics, yet it is rarely recognised as such. Indeed, out of all the research devoted to explaining financial market instability, very little has involved looking at what happens physiologically to traders when caught up in a bubble or a crash. This is an extraordinary omission, comparable to studying animal behaviour without looking at an animal in the wild, or practising medicine without ever looking at a patient. I am, however, convinced we should be looking at traders’ biology. I think we should take seriously the possibility that the extreme overconfidence and risk-taking displayed by traders during a bubble may be pathological behaviour calling for biological, even clinical, study.

The 1990s were a decade ripe for such research. They gave us the folly of the dot.com bubble as well as the phrase that best described it – ‘irrational exuberance’. This term, first used by Alan Greenspan in a speech delivered in Washington in 1996 and subsequently given wide currency by the Yale economist Robert Shiller, means much the same thing as an older one, ‘animal spirits’, coined in the 1930s by Keynes when he gestured towards some ill-defined and non-rational force animating entrepreneurial and investor risk-taking. But what are animal spirits? What is exuberance?

In the nineties, one or two people did suggest that irrational exuberance might be driven by a chemical. In 1999 Randolph Nesse, a psychiatrist at the University of Michigan, bravely speculated that the dot.com bubble differed from previous ones because the brains of many traders and investors had changed – they were under the influence of now widely prescribed antidepressant drugs, such as Prozac. ‘Human nature has always given rise to booms and bubbles followed by crashes and depressions,’ he argued. ‘But if investor caution is being inhibited by psychotropic drugs, bubbles could grow larger than usual before they pop, with potentially catastrophic economic and political consequences.’ Other observers of Wall Street, following a similar line of thought, pointed the finger at another culprit: the increasing use of cocaine among bankers.

These rumours of cocaine abuse, at least among traders and asset managers, were mostly exaggerated. (Members of the sales force, especially the salesmen responsible for taking clients out to lap-dancing bars till the wee hours of the morning, may have been another matter.) As for Nesse, his comments received some humorous coverage in the media, and when he spoke at a conference organised by the New York Academy of Sciences a year later he seemed to regret making them. But I thought he was on the right track; and to me his suggestion pointed to another possibility – that traders’ bodies were producing a chemical, apparently narcotic, that was causing their manic behaviour. What was this bull-market molecule?

I came across a likely suspect purely by chance. During the later years of the dot.com era I was fortunate enough to observe some fascinating research being conducted in a neuroscience lab at Rockefeller University, a research institution hidden on the Upper East Side of Manhattan, where a friend, Linda Wilbrecht, was doing a Ph.D. I was not at Rockefeller in any formal capacity, but when the markets were slow I would jump in a taxi and run up to the lab to observe the experiments taking place, or to listen to afternoon lectures in Caspary Auditorium, a geodesic dome set in the middle of that vine-clad campus. Scientists in Linda’s lab were working on what is called ‘neurogenesis’, the growth of new neurons. Understanding neurogenesis is in some ways the Holy Grail of the brain sciences, for if neurologists could figure out how to regenerate neurons they could perhaps cure or reverse the damage of neuro-degenerative diseases such as Alzheimer’s and Parkinson’s. Many of the breakthroughs in the study of neurogenesis have taken place at Rockefeller.

There was another area of the neurosciences where Rockefeller had made a historic contribution, and that was in research on hormones, and specifically their effects on the brain. Many of the breakthroughs in this field had been made by scientists addressing very specific issues in neuroscience, but today their results may help us understand irrational exuberance, for the bull-market molecule may in fact be a hormone. And if that is the case, then by a delightful coincidence, at the very moment in the late 1990s when Wall Street was asking the question ‘What is irrational exuberance?’, uptown at Rockefeller scientists were working on the answer.

So what exactly are hormones? Hormones are chemical messengers carried by the blood from one tissue in the body to another. We have dozens of them. We have hormones that stimulate hunger and ones that tell us when we are sated; hormones that stimulate thirst and ones that tell us when it is slaked. Hormones play a central role in what is called our body’s homeostasis, the maintenance of vital signs, like blood pressure, body temperature, glucose levels, etc., within the narrow bands needed for our continued comfort and health. Most of the physiological systems that maintain our internal chemical balance operate pre-consciously, in other words without our being aware of them. For instance, we are all blissfully unaware of the Swiss-watch-like workings of the system controlling the potassium levels in our blood.

But sometimes we cannot maintain our internal balance through these silent, purely chemical reactions. Sometimes we need behaviour; sometimes we have to engage in some sort of physical activity in order to re-establish homeostasis. When glucose levels in our blood fall, for example, our bodies silently liberate glucose deposits from the liver. Soon, however, the glucose reserves burn off, and the low blood sugar communicates itself to our consciousness by means of hunger, a hormonal signal that spurs us to search for food and then to eat. Hunger, thirst, pain, oxygen debt, sodium hunger and the sensations of heat and cold, for example, have accordingly been called ‘homeostatic emotions’. They are called emotions because they are signals from the body that convey more than mere information – they also carry a motivation to do something.

It is enlightening to see our behaviour as an elaborate mechanism designed to maintain homeostasis. However, before we go too far down the path of biological reductionism, I have to point out that hormones do not cause our behaviour. They act more like lobby groups, recommending and pressuring us into certain types of activity. Take the example of ghrelin, one of the hormones regulating hunger and feeding. Produced by cells in the lining of your stomach, ghrelin molecules carry a message to your brain saying in effect, ‘On behalf of your stomach we urge you to eat.’ But your brain does not have to comply. If you are on a diet, or a religious fast, or a hunger strike, you can choose to ignore the message. You can, in other words, choose your actions, and ultimately you take responsibility for them. Nonetheless, with the passing of time the message, at first whispered, becomes more like a foghorned bellow, and can be very hard to resist. So when we look at the effects of hormones on behaviour and on risk-taking – especially financial risk-taking – we will not be contemplating anything like biological determinism. We will be engaged rather in a frank discussion of the pressures, sometimes very powerful, these chemicals bring to bear on us during extreme moments in our lives.

One group of hormones has particularly potent effects on our behaviour – steroid hormones. This group includes testosterone, oestrogen and cortisol, the main hormone of the stress response. Steroids exert particularly 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’.