The Secret Life of the Mind: How Our Brain Thinks, Feels and Decides

Monkeys played this game thousands of times, while the researchers recorded their neuronal activity as reflected by the electrical currents produced in their brains. After studying this exercise for many years, and in many variations, they revealed the three principles of Turing’s algorithm for decision-making:

(1) A group of neurons in the visual cortex receives information from the retina. The neuron’s current reflects the quantity and direction of movement in each moment, but does not accumulate a history of these observations.

(2) The sensory neurons are connected to other neurons in the parietal cortex, which amass this information over time. So the neuronal circuits of the parietal cortex codify how the predisposition towards each possible action changes over time during the course of making the decision.

(3) As information favouring one option accumulates, the parietal cortex that codifies this option increases its electrical activity. When the activity reaches a certain threshold, a circuit of neurons in structures deep in the brain – known as basal ganglia – set off the corresponding action and restart the process to make way for the next decision.

The best way to prove that the brain decides through a race in the parietal cortex is by showing that a monkey’s response can be conditioned by injecting a current into the neurons that codify evidence in favour of a certain option. Shalden and Newsome did that experiment. While one monkey was watching a cloud of dots that moved completely randomly, they used an electrode to inject an electrical current into the parietal neurons that codify movement to the right. And, despite the senses indicating that movement was tied in either direction, the monkeys always responded that they were moving to the right. This is like emulating electoral fraud, manually inserting certain votes into the ballot box.

Additionally, this series of experiments allowed for the identification of three fundamental traits of the decision-making process. What relationship is there between the clarity of the evidence and the time we take to make a decision? How are options biased by prejudices or prior knowledge? When is there enough evidence in favour of one option to call the race? The answers to these three questions are interrelated. The more incomplete the information is, the slower the accumulation of evidence will be. In the moving-dot experiment, when almost all the dots move at random, the ramp of activation in the neurons in the parietal cortex that amass the evidence is not very steep. And if the threshold of evidence needed remains the same, it will take more time to cross it; which is to say, to reach the same degree of reliability. The decision cooks over a slow flame, but eventually it will reach the same temperature.

And how is the threshold established? Or, to put it another way, how does the brain determine when enough is enough? This depends on a calculation that the brain makes in a stunningly precise way, by pondering the cost of making a mistake and the time available for the decision-making.

The brain determines that threshold in order to optimize the gains from a decision. To do so it combines neuronal circuits that codify:

(1) The value of the action.

(2) The cost of time invested.

(3) The quality of the sensory information.

(4) An endogenous urgency to respond, something that we recognize as anxiety or impatience to decide.

If, in the random-dots game, mistakes are punished severely, the players (humans or monkeys) raise the threshold, taking more time to decide and accumulating more evidence. If, on the other hand, mistakes don’t count, then the players lower that same threshold, adopting again the best strategy, which here is to respond as quickly as possible. The most notable aspect of this adaptive adjustment is that in most cases it is not conscious, and often far more optimal than we would imagine.

Consider, for example, a driver stopping at a traffic light. The driver’s brain is making a great number of estimations: the probability that the light may turn amber or red, the distance to the crossing, the speed of the car, the effectiveness of the brakes, the traffic etc. Not only this: the driver´s brain is also pondering the urgency, the consequences of an accident … In the vast majority of cases (except when something goes wrong and the monitoring system of the brain takes control) these considerations are not explicit. We are not aware of all these calculations. Yet our brains do make this sophisticated calculus, which results in a decision of when and how hard we will hit the brake pedal. This specific example reveals a general principle: decision-makers know much more than they believe they do.

In contrast with this, in some conscious deliberations (which are the only ones we do remember at the end of the day) the brain often sets a very inefficient threshold to reach a decision. We all remember having slept too long on some matters which did not require that much deliberation. For example, most of us recall deliberating ad infinitum in a restaurant between two choices even if deep inside we know we would greatly enjoy either of those two options.

Turing in the supermarket

Even though in the laboratory we study simple decisions, what we are ultimately more interested in revealing is how the brain makes everyday decisions: the driver who decides whether or not to jump an amber light; the judge who condemns or exonerates a defendant; the voter who casts a ballot for one candidate or another; the shopper who takes advantage of or falls victim to a special deal. The conjecture is that all of these decisions, despite belonging to different realms and having their own idiosyncrasies, are the result of the same decision-making mechanism.

One of the main principles of this procedure, which is at the heart of Turing’s design, consists in how one realizes when it is time to stop gathering evidence. The problem is reflected in the paradox described by a medieval philosopher, Jean Buridan: a donkey hesitates endlessly between two identical piles of hay and, as a result, ends up dying of hunger. In fact, the paradox presents a problem for Turing’s pure model. If the number of votes in favour of each alternative is identical, the cerebral race is stuck in a tie. The brain has a way of avoiding the tie: when it considers that sufficient time has passed, it invents neuronal activity that it randomly distributes among the circuits that codify each option. Since this current is random, one of the options ends up having more votes and, as such, wins the race. It’s as if the brain tossed a coin and let fate break the tie. How much time is reasonable for making a decision depends on internal states of the brain – for example, if we are more or less anxious – and on external factors that affect how the brain counts the time.

One of the ways that the brain estimates time is simply by counting pulses: steps, heartbeats, breaths, the swinging of a pendulum or music’s tempo. For example, when we exercise, we mentally estimate a minute faster than when we are at rest, because each heartbeat – and therefore each pulse of our inner clock – is quicker. The same happens with tempo in music. The clock accelerates with the rhythm and, thus, time passes more rapidly. Do these changes in our internal clock make us decide more quickly and lower our decision threshold?

Indeed, music has much more direct consequences for our decisions than we recognize. We drive, shop and walk differently depending on the music we are listening to at the time. As the musical tempo rises, our decision-making threshold lowers and as a result risk increases in almost every decision. Drivers change lanes more frequently, go through more amber lights, overtake and exceed the speed limit more while driving as the speed of the music they are listening to increases. Musical tempo also dictates the amount of time we are willing to wait patiently in a waiting room or the number of products we tend to buy in a supermarket. Many supermarket managers know that the piped-in music is a key to sales and use that to their advantage, with no need to be familiar with Turing’s work. That’s how predictable our decision-making machine is, yet we are almost completely unaware of its workings.

Another key factor that affects the decision-making machine is determining where the race begins. When there is a bias towards one of the alternatives, the neurons that accumulate information in its favour start with an initial electrical charge, which is similar to giving them a head start in the race. In some cases, biases can have a fundamental influence; for example, in the decision to donate organs.

Demographic studies of organ donation group different countries into two classes: those in which almost all the inhabitants agree to donate organs, and another in which almost no one does. It doesn’t take a master statistician to understand that what’s striking is the absence of intermediate classes. The reason turns out to be extremely simple: what ends up determining whether a person chooses to donate organs is the wording on the form. In the countries where the form says: ‘If you wish to donate organs, sign here’, no one does. On the other hand, in countries where it says: ‘If you do NOT wish to donate organs, sign here’, almost everyone donates. The explanation for both phenomena comes from an almost universal trait that has nothing to do with religion or life and death but rather just that no one fills out the form completely.

When we are offered a wide variety of options, they don’t all start running from the same point; those that are given by default begin with an advantage. If, in addition, the problem is one that is hard to resolve, meaning that evidence in favour of any of the options is scarce, the one that started out with the advantage wins. This is a very clear example of how governments can guarantee freedom of choice but, at the same time, bias – and, in practice, dictate – what we decide. But this also reveals a characteristic of human beings, be they Dutch, Mexican, Catholic, Protestant or Muslim: our decision-making mechanism collapses when faced with difficult situations. Then we merely accept what we are offered, by default.

The tell-tale heart

Until now we’ve talked about decision-making processes as if they were all of one class, governed by the same principles and carried out in the brain by similar circuits. However, we all perceive that the decisions we make belong to at least two qualitatively distinct types; some are rational and we can put forward the arguments behind them. Others are hunches, inexplicable decisions that feel as if they are dictated by our bodies. But are there really two different ways of deciding? Is it better to choose something based on our intuitions, or to carefully and rationally deliberate each decision?

In general we associate rationality with science, while the nature of our emotions seems mysterious, esoteric and essentially inexplicable. We will topple this myth with a simple experiment.

Two neuroscientists, Lionel Naccache and Stanislas Dehaene – my mentor in Paris – did an experiment in which they flashed numbers on screens so fleetingly that the participants believed they’d seen nothing. This type of presentation, which doesn’t activate consciousness, is called subliminal. Then they ask the participants to say if the number is higher or lower than five and, much to their own surprise, they answer correctly in most cases. The person making the decision perceives it as a hunch, but from the experimenter’s perspective it is clear that the decision was induced unconsciously with a mechanism very similar to that of conscious decision-making.

Which is to say that, in the brain, hunches aren’t so different from rational decisions. But the previous example doesn’t capture all the richness of the physiology of unconscious decisions. In this case, popular expressions such as ‘trust your heart’ or ‘go with your gut feelings’ turn out to be quite accurate and shed light on how intuitions are forged.

All it takes to understand this is putting a pencil between your teeth, lengthwise. Inevitably, your lips will rise in an imitation of a smile. This is obviously a mechanical effect, not a reflection of an emotion. But that doesn’t matter, it still gives a certain sense of wellbeing. The mere gesture of the smile is enough. A film scene will seem more entertaining to us if we watch it with a pencil held in our mouth that way than if we hold it between our lips, as if scowling. So, deciding whether something is fun or boring does not only originate in an evaluation of the external world, but in visceral reactions produced in our internal worlds. Crying, sweating, trembling, increasing heart rate or secreting adrenaline are not merely reactions by the body to communicate an emotion. Instead, the brain reads and identifies these bodily variables to encode and produce feelings and emotions.

That corporeal states can affect our decision-making process is a physiological and scientific demonstration of what we perceive as a hunch. When making a decision unconsciously, the cerebral cortex evaluates different alternatives and, in doing so, estimates the possible risks and benefits of each option. The result of this computation is expressed in corporeal states through which the brain can recognize risk, danger or pleasure. The body becomes a reflection and a resonating chamber of the external world.

The body in the casino and at the chessboard

The key experiment showing how decisions are based on hunches was done with two decks of cards.

As in so many board games, this experiment employs ingredients from real life decision-making: winnings, losses, uncertainty and risk. The game is simple but unpredictable. In each turn, the player merely chooses which deck to pick a card from. The number of the card chosen indicates the coins that the player wins (or loses if it’s negative). Since the cards are turned face down, the player has to evaluate, over the course of the entire experiment, which of the two decks is more profitable.

This is like someone in a casino who has to choose between two one-armed bandits just by observing how many times and how much each one pays out over a period of time. But, unlike in the casino, this game thought up by a neurobiologist, Antonio Damasio, is not purely random: there is one deck that on average pays out more than the other. If this rule is discovered, then the next step is simple: always choose the deck that pays more. Lo and behold, an infallible system.

The difficulty lies in the fact that the player has to discover this rule through pondering a long history of payouts amid large fluctuations. After much practice, almost everyone discovers the rule, is able to explain it and, naturally, starts to choose cards from the correct deck every time. But the real finding happens along the way to this discovery, among intuitions and hunches. Even before being able to articulate the rule, the players start to play well and more frequently choose cards from the correct deck. In this phase, despite playing much better than when they were choosing randomly, the players cannot explain why they opt for the correct deck (the one that pays out more in the long term). Sometimes they don’t even know they are choosing one deck more than the other. But unequivocal signs show up in their bodies. In this part of the experiment, when players are about to choose the incorrect deck, their skin conductance increases, indicating a rise in sweating, which is in turn a reflection of an emotional state. Which is to say that the players cannot explain that one of the decks gives better results than the other, but their bodies already know it.

My colleague María Julia Leone, a neuroscientist and international chess master, and I carried out this experiment on the chessboard, following the Borgesian concept of chess as a metaphor for life. Two masters face off. They have thirty minutes to make a series of decisions that will organize their armies. On the board, it is a battle to the death and emotions are running high. During the game we trace the players’ heartbeats. Heart rate – just like stress – increases over the course of the game, as time runs out and the end of the battle approaches. Their heart rates also spike when their opponent commits an error that will decide the outcome of the game.

But the most significant discovery we made was this: a few seconds before the players made a mistake, their heart rate changed. This means that in a situation with countless options, with a complexity that is similar to that of life itself, the heart panics before making a bad decision. If the players could recognize that, if they were able to listen to what their hearts are telling them, they could perhaps avoid many of their errors.

This is possible because the body and the brain hold the keys to decision-making long before we are consciously aware of those elements; the emotions expressed in our bodies function as an alarm to alert us to possible risks and mistakes. This destroys the idea that intuition belongs to the realm of magic or soothsaying. There is no conflict between hunches and science; in fact, quite the opposite: intuition functions hand in hand with reason and deliberation, fully in the realm of science.

Rational deliberation or hunches?

Once we have discovered that hunches and intuitions are unconscious deliberations we can proceed to a question of more practical relevance. When should we trust our hunches and intuitions and when not? For those questions that matter most to us, should we trust our hunches or our rational deliberations?

The answer is conclusive: it depends. A social psychologist, Ap Dijksterhuis, found, in an experiment that is still generating controversy, that the complexity of a decision is what dictates when it’s best to deliberate consciously or act intuitively. Dijksterhuis found that to be the rule both in ‘mock’ decisions in the lab and in real-life decisions.

In the laboratory, he constructed a game in which participants had to evaluate two options – for example, two cars – and choose which was preferable in terms of utility. Sometimes, the two alternatives only differed in price. In that case, the decision was simple: the cheaper one was better. Then the problem became progressively more complex, when the two cars varied not only in price, but in petrol consumption, safety, comfort, risk of theft, engine capability and pollution levels.

Dijksterhuis’s most surprising discovery was that when there are many elements in play, hunches are more effective than deliberation. The same pattern appears in decisions in the real world. This was observed in an experiment whereby people who had just bought toothpaste – undoubtedly one of life’s easier choices – were asked how they had made their decision. A month later, those who had pondered their decisions were more satisfied than those who hadn’t. On the other hand, they observed the opposite result when interviewing people who had just bought furniture (a complex decision, with many more variables such as price, size, quality, aesthetic appeal). Just like in the lab, those who thought less chose better.

The methodologies of these experiments are quite different, but the conclusion is the same. When we make a decision by carefully thinking over a small number of elements, we choose better if we take our time. Yet when the problem is complex, in general we make better choices by following our intuition than if we stew over it.

The conscious mind is fairly limited in size and can hold little information. Our unconscious, however, is vast. This explains why when making decisions with few variables in play – price, quality and size of a product, for example – we are best served by thinking it over before acting. In situations where we can mentally evaluate all the elements at the same time, the rational decision is more effective, and therefore better. We also can see why – when there are many more variables in play than our conscious mind can juggle at once – our unconscious, rapid, intuitive decisions are more effective, even when based on approximated calculations.

Sniffing out love

Perhaps the most important and complex decisions that we make are social and emotional. It may seem strange, almost absurd, to decide whom to fall in love with in a deliberate way, by some arithmetic evaluation of arguments for and against that person we feel so drawn to. That’s just not how it works. We fall in love for reasons that are generally mysterious and can only be determined sketchily after some time has passed.

At pheromone parties, each participant sniffs the clothing that’s been worn for a few days by other guests. Based on the odour print that attracts them, they decide whom to approach at the party. Choosing this way seems natural because we associate our sense of smell with intuition, like when we say that ‘something smells fishy.’ And because we all recognize how evocative the intimate and indescribable scent of our lover’s sheets is. But, at the same time, it’s weird because, obviously, our sense of smell isn’t the most precise of our senses. So it seems fairly likely that someone could be sorely disappointed by the partner their sniffing leads them to, and run off cursing their ridiculous nose.

Claus Wedekind, a Swiss biologist, made a phenomenal experiment out of this game. He had a group of men wear the same T-shirt for several days, with no deodorants or perfumes. Then a series of women smelled the shirts and articulated how pleasurable they found each scent – and, of course, he also did the reverse, having the men sniff the women’s well-worn T-shirts. Wedekind wasn’t just fishing with this experiment to see what he would find: he had based it on a hypothesis constructed from observing the behaviour of rodents and other species. He was exploring the premise that as far as scent, taste and unconscious preferences were concerned, we are very similar to our inner ‘beasts.’

Each individual has a different immune repertoire, which explains, in part, why, when exposed to the same virus, some of us get sick and others don’t. We can think of each immune system as a shield. If two shields are placed one on top of the other protecting the same space, they become redundant. However, two shields covering different, contiguous spaces can together protect a larger surface area. The same idea can be transferred – with certain drawbacks that we will ignore for the moment – to the immune repertoire: two individuals with very different immune repertoires give rise to progeny with a more effective immune system.

In rodents, who use their sense of smell much more than we do when choosing a mate, the preference largely follows a simple rule governed by this principle: they tend to choose mates with a different immune repertoire. This was the basis for Wedekind’s experiment. He measured each participant’s MHC (major histocompatibility complex), a family of genes involved in the differentiation between our own and others’ immune systems. And the extraordinary result is that when we judge by our sense of smell, we do so according to the same premise as our rodent cousins: on average, women will be more attracted to the scent of men who have a different MHC. So pheromone partiesfn2 promote diversity. At least in terms of immune repertoires.

But this rule has a notable exception. A female mouse’s scent preferences invert when she is pregnant. Then she prefers the smell of mice with MHCs that are similar to hers. The simplified, narrative version of this result is that while the search for complementariness can be beneficial when mating, once there is already a baby in the womb it makes sense to remain close to a known nest, among kin, with those who are similar.

Does the same shift in olfactory preference happen with women? It seems plausible since, in the midst of the hormonal revolution that occurs during a woman’s pregnancy, her changes in smell and taste perception are among the most distinctive effects. Wedekind studied how olfactory preference changed when a woman is taking birth control pills with steroids that stimulate a very similar hormonal state to pregnancy. Thus it was discovered that, just like in rodents, the result was turned on its head, and the smell of T-shirts worn by men with similar MHCs became more appealing.