The neuroscience of optimism – how the brain creates a rosy outlook

In 1979, a crucified Eric Idle advised movie-goers to always look on the bright side of life. It seems that he needn’t have bothered. Psychological experiments have consistently shown that as a species, our minds are awash with a pervasive optimism.

We have an innate tendency to look on the bright side of life.We expect our future successes to overpower our past ones. Compared to an imaginary Joe Bloggs, we deem ourselves likely to live longer, more likely to have a successful career and less likely to suffer divorce or ill health. Even the most cynical of minds had a tendency for making similar, overconfident predictions.

Now, Tali Sharot and colleagues form New York University have pinpointed a neural circuit in the brain that generates this glass-half-full outlook.

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Genes affect our likelihood to punish unfair play

As a species, we value fair play. We’re like it so much that we’re willing to eschew material gains in order to punish cheaters who behave unjustly. Psychological games have set these maxims in stone, but new research shows us for the first time, that this sense of justice is, to a large extent, influenced by our genes.

When it comes to demonstating our innate preference for fair play, psychologists turn to the ‘Ultimatum Game‘, where two players bargain over a pot of money. The ‘proposer’ suggests how the money should be divided and the ‘receiver’ can accept of refuse the deal. If they refuse, neither player gets anything and there is no room for negotiation. In a completely rational setting, the proposer should offer the receiver as little as possible, and the receiver should take it – after all, a very little money is better than none at all.

Of course, that’s not what happens. Receivers typically abhor unfair offers and would rather that both parties receive no money than accept a patronisingly tiny amount. Across most Western countries, proposers usually offer the receivers something between 40% and 50% of the takings. Any offers under 10% are almost always rejected.

The uniformity of responses across Western countries suggests that culture has a strong effect on how people play the game, but until now, no one had looked to see how strongly genes asserted their influence. Bjorn Wallace and colleagues from the Stockholm School of Economics decided to do just that, and they used the classic experiment for working out heritability – the twin study.

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Why are women better at food shopping than men?

Men do better than women at most tests of spatial awareness, but not all. A new study set in a farmer’s market shows that women outperform men at remembering the locations of food, particularly the most calorific ones.

Our evolutionary history makes women better at finding food in supermarkets than menWhen men and women do the grocery run, their evolutionary histories play out among the aisles of food in subtle ways. Women are more likely to remember where things are; men are better at plotting efficient paths through the smorgasbord of choice. These different abilities are the result of evolutionary adaptations that took place when we were still hunting and gathering.

The evolution of sex differences

The brains of men and women are clearly different, and rarely more so than in the realms of spatial awareness. In most tests of spatial ability, men routinely outperform women. But to Irvin Silverman and Marion Eals, this crude assertion crumbled under an evolutionary spotlight.

In 1992, the duo noted that our mental abilities were not created from a vacuum – they evolved to allow us to cope with different adaptive challenges. And for the men and women of our dim evolutionary past, these challenges were very different.

Back in the day, when we were still living as hunter-gatherers, men did most of the hunting while women excelled at gathering. And these jobs required very different spatial skills. Hunters, for example, needed to chase their prey over unfamiliar and winding routes; once they had killed, they needed to work out the quickest route home.

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Five-month-old babies prefer their own languages and shun foreign accents

Discriminating against people who do not speak your language is a big problem. A new study suggests that the preferences that lead to these problems are hard-wired at a very young age. Even five-month-old infants, who can’t speak themselves, have preferences for native speakers and native accents.

The human talent for language is one of our crowning evolutionary achievements, allowing us to easily and accurately communicate with our fellows. But as the Biblical story of the Tower of Babel relates, linguistic differences can serve to drive us apart and act as massive barriers between different social groups.

The Tower of Babel story highlights the conflicts that can arise when people don’t speak the same language.These barriers can give rise to linguistic discrimination, a far more insidious problem that it seems at first. Language-based prejudices have led to horrific acts of human abuse, and even civil wars. Genocide often finds itself paired with linguicide, since a race can be killed off more thoroughly if their language follows them.

Even today, people in a linguistic minority can find themselves denied access to healthcare, or at a disadvantage when looking for jobs. The issue cuts to the heart of several ongoing debates, from the role of second languages in education to whether immigrants must become fluent in the tongue of their host country.

Early preferences

It should therefore be unsurprising to learn that we have strong preferences for our own language and for those who speak it. But Katherine Kinzler and colleagues from Harvard University, have found that we develop these preferences from an incredibly young age, before we can speak ourselves, and well before we can even hope to understand the social issues at stake.

Kinzler tested 24 infants, aged 5 to 6 months, from households that only spoke English, to see if they had any linguistic preferences. Each toddler watched videos of two women, one speaking English and the other, Spanish. The women were all bilinguals and swapped the language they used in different trials to make sure that the babies weren’t showing preferences for physical traits like skin colour.

The babies were then shown the two women side by side, but no longer speaking. They strongly expressed their preference for the English speakers by gazing at their screen for a longer time (measuring gaze time like this is a standard test used by child psychologists).

Once developed in early infancy, these preferences stick around into childhood, and most probably well beyond that. In very similar experiments, Kinzler found that older infants (10 months or so) prefer to accept toys from a woman who spoke their native language.

Even young infants can discriminate between their language and others.The babies, from either Boston or Paris, were shown alternating films of an English or French-speaking woman, who spoke for a while and then silently offered the child a toy. Two real toys then appeared on the table in front of the infant, and they were twice as likely to pick the one in front of the native speaker.

So even though the offering of the toy involved no spoken words, the infants still gravitated towards the woman who had spoken earlier in their familiar tongue.

Different accents

Infants can even pick up on subtle differences in dialect. Even when two speakers are talking in the same language, 5-month old infants will prefer someone who speaks with a native accent to someone who speaks with a foreign twang. Older children (5 years or so) will similarly prefer to befriend another child who speaks with the same accent.

At that age, children will have barely any understanding of the social circumstances that leads to different groups of people speaking the same language in different ways. And it’s unlikely that their parents had much influences, since even the 5-month-old toddlers had these preferences.

These early preferences can act as the foundations for more destructive behaviours and conflicts later on in life. But we must be very careful – an instinctive basis for a behaviour does not in any way justify it.

Instead, by telling us about the basis of linguistic prejudices, these results suggest that we must work even harder to overcome them. If they are hard-wired from an early age, then education from an early age seems like a sensible first step.

Perhaps, exposure to multiple languages early in life can soften these preferences, and it would be fascinating to see if the same results hold for babies from bilingual households.

More on languages, child development, and social conflicts:
Babies can tell apart different languages with visual cues alone
Experience tunes a part of the brain to the shapes of words
In conflicts over beliefs and values, symbolic gestures matter more than reason or money

Reference: Kinzler, Dupoux & Spelke. 2007. The native language of social cognition. PNAS 104: 12577-12580

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Are women more talkative than men?

In 2006, a best-selling book claimed that women are over three times more talkative than men. But a new study, the first to actually measure how many words men and women say in natural conversations, has resigned this statistic to the urban myth bin.

In ‘The Female Brain’, author Louann Brizendine stated that women use about 20,000 words a day while men speak a mere 7,000. Predictably, the media loved the story and through widespread reporting, this statistic has almost reached the status of urban myth.

Women and men are just as chatty as each other.The success of Brizendine’s statistic as a meme is surely helped by the fact that it ‘sounds about right’, much like the infamous myth that Inuits have multiple words for snow. In this case, our stereotyped view of gender says that women are better at expressing themselves than men, who are content to grunt and repress their way through emotional experiences.

In the light of this common wisdom, Brizendine’s ‘fact’ seems like pointing out the obvious, and she helped matters along by providing a vague explanation.

As testosterone moulds the developing brain of male embryos, it slows the development of areas of the brain involved in emotion and communication. As adults, men pay the price for this and struggle to express themselves.

But scientists were not impressed. The journal Nature said that, “despite the author’s extensive academic credentials, The Female Brain disappointingly fails to meet even the most basic standards of scientific accuracy and balance.”

As it happens, Brizendine didn’t really have any data to go on. Until now, no studies have recorded the natural conversations of large groups of people over long periods of time, which means that the statistic in the book is a guess at best.

Evidence at last

For hard evidence, we can now turn to Matthias Mehl from the University of Arizona, and colleagues from the Universities of St Louis and Texas. They had a wealth of data to study. Over the past decade, they have been running experiments which involved unobtrusively recording natural conversations.

Their recorder is an electronic device, delightfully called the EAR (electronically activated recorder). The wearer keeps the EAR on for several days and every 12.5 minutes, it records a thirty-second snippet of sound. The researchers transcribe any conversations captured by the device, and use this to estimate the total number of words spoken throughout the day.

Men may have difficulty expressing themselves but that doesn’t mean that they’re any less talkative than women.Between 1998 and 2004, the group amassed recordings from over 210 women and 186 men. When they did a word count of the recordings, the results were very clear – both men and women use about 16,000 words a day.

Women used about 215 words more than average and men used 331 less, but this difference was not statistically significant. Neither gender was more verbose than the other.

Mehl admits that there are certain limitations to their data. For a start, all the people in the studies were university students between the ages of 17 and 29. It may be that larger differences would show up in people from lower educational background.

But not according to Brizendine’s theory – she suggested that women are more talkative because of fundamental biological differences that happen in the womb. If she was right, you wouldn’t expect these differences to be so completely masked in any socioeconomic group.

The final caveat is that only American and Mexican students were tested. In other countries, where gender equality is a much more troubling issue, there may be starker differences.

But in North America at least, women are not more talkative than men. Indeed, there may well be much larger differences between different men and women than there are between the two genders.

The moral of this story is that repeating a statistic doesn’t transform it into fact – we need experiments and good, hard data for that.

Reference: Mehl, Vazire, Esparza, Slatcher & Pennebaker. 2007. Are women really more talkative than men? Science

Related posts on gender issues and psychology:
Opinion: Women in science or “Why those at the top should mind what they say”
In conflicts over beliefs and values, symbolic gestures matter more than reason or money
Opinion: Discovery of ‘fat gene’ highlights stigma against obese people

The evolution of animal personalities – they’re a fact of life

Animals have distinct personalities and temperaments, but why would evolution favour these over more flexible and adaptible mindsets? New game theory models show that animal personalities are a natural progression from the choices they make over hwo to live and reproduce.

Any pet owner, wildlife photographer or zookeeper will tell you that animals have distinct personalities. Some are aggressive, others are docile; some are bold, others are timid.

An animal’s reproductive decisions can determine if it is a hawk…In some circles, ascribing personalities to animals is still a cardinal sin of biology and warrants being branded with a scarlet A (for anthropomorphism). Nonetheless, scientists have consistently found evidence of personality traits in species as closely related to us as chimpanzees, and as distant as squid, ants and spiders.

These traits may exist, but they pose an evolutionary puzzle because consistent behaviour is not always a good thing. The consistently bold animal could well become a meal if it stands up to the wrong predator, or seriously injured if it confronts a stronger rival. The ideal animal is a flexible one that can continuously adjust its behaviour in the face of new situations.

And yet, not only do personality types exist but certain traits are related across the entire animal kingdom. Aggression and boldness toward predators are part of a general ‘risk-taking’ personality that scientists have found in fish, birds and mammals.

Life decisions affect personality

Max Wolf and colleagues from The University of Groningen, Netherlands, have found a way to explain this discrepancy. Using game theory models, they have shown that personalities arise because of the way animals live their lives and decide when to reproduce.

For an animal, success is measured achieved through living long enough to reproduce, and individuals constantly gamble their current success against their future one. They could reproduce now, or defer it to a later time when resources are more abundant.

The crux of Wolf’s theory is that those with a stable, assured future have more to lose by gambling, and are likely to be more risk-averse. Those with little to lose can afford to live fast and die young.

A model personality

Wolf tested this idea by using a mathematical model to simulate these choices and their consequences. The protagonist of his model is a fictional animal that lives in an area with many territories, some rich in food and others lacking it.

The animal can choose how thoroughly it wants to explore its habitat. If it is adventurous, it could find a lush and bountiful territory, but it will have less energy to raise young, and must postpone this to the following year. That may not be so bad – its new home will give it a ripe, long life and it will have many opportunities for breeding.

or a dove.He found that simulated animals picked one of two stable strategies. Some decided to explore thoroughly and hope for greater reproductive success in the future. Others decided to stay put, have young now and make the best of things, poor resources be damned.

Wolf then modelled how these two groups would react to decisions about risk, in a classic hawk-dove experiment. When faced with a predator or a rival, the animal could run away or back down (dove), which takes time and could lose it feeding opportunities or its territory. If it stood and fight (hawk), the likelihood of death or injury was greater but so were the rewards.

Sure enough, the explorers who were investing on future success, consistently evolved to be docile, timid and risk-averse, while those who reproduced immediately consistently became bold and aggressive. These patterns held up under a wide range of simulated conditions. Over time, they gave rise to stable individual differences and behaviour traits that were consistently linked with each other, the foundations of personality.


In New Scientist’s coverage of this story, Judy Stamp from the University of California, Davis, criticises Wolf’s work for only explaining extremes of personality. Obviously, animals are not always black hawks or white doves, but many shades in-between.

But Wolf’s study answers this too. In the most advanced version of his model, he accounted for the fact that behaviours are governed by many heritable genes. This generated a much more realistic and continuous spectrum of personalities. Even with this more plausible model, the same principle applied – the more an animal had to lose, the fewer risks it was prepared to take.

Wolf is now keen to see his theory tested in the field. He suggests that many other behaviour traits could be linked to aggression or boldness. Individuals that invest heavily in the present may be more likely to guard nests, care for their young or woo mates with conspicuous and costly displays.


Reference: Wolf, van Doorn, Leimar & Weissing. 2007. Life-history trade-offs favour the evolution of animal personalities. Nature 447: 581-584.

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Impulsive minds are primed for drug addiction

Impulsive rats are improving our understanding of human drug addiction. Because of differences in the way their brains process dopamine, these animals are predisposed to addiction, even before they’ve touched a drug.

We’ve all acted impulsively before, and we have the horrendous clothes, echoing bank accounts and hilarious memories to show for it. But science is beginning to show that impulsive people may be particularly vulnerable to drug addiction, and there is little funny or harmless about that.

Millions of people around the world are addicted to drugs like nicotine, cocaine, heroin and alcohol.According to Government statistics, half a million people in the UK are addicted to class A drugs like cocaine, heroin and amphetamines.

All too often, drug addiction and other compulsive disorders like obesity are dismissed as issues of ‘willpower’ and those who succumb to temptation are labelled as ‘weak’.

But this attitude is at best wrong, and at worst stigmatising and self-righteous. And it provides no clues for ways of helping people with these problems.

In fact, the evidence suggests that drug addiction is linked to certain personality traits. Being impulsive is possibly one of them, and being keen to seek out new sensations (often described as “living life to the full”) is another.

But do these traits drive people towards drug addiction, or are they a result of the drugs themselves?

Some scientists have suggested that long-term drug use impairs our prefrontal cortex, a part of our brain that helps to suppress our basic urges, and is essential for appropriate social behaviour. It’s the mental equivalent of the angel on our shoulders. By relieving us of this restraining effect, drug use could lead to impulsive, reckless and anti-social behaviour.

Impulsive people are more likely to become addicted to drugs like cocaine.But a new animal study suggests that it works the other way round too. Innate differences in personality traits can predispose individuals to addictive drugs, even before a single molecule has entered their system.

Jeffrey Dalley, Trevor Robbins and colleagues at the University of Cambridge studied a dozen rats, who were cocaine virgins at the start of the experiment. The rats were trained to associate a light with the arrival of food; when it came on, the animals received food if they waited and pressed a button.

Some of the rats were twice as likely to prematurely press the button than others, allowing Dalley to separate them into an ‘impulsive’ and a ‘non-impulsive’ group. A brain scan revealed key differences in the brains of the two groups, particularly in the ventral striatum, a part of the brain involved in reward, pleasure and addiction.

In this region, the impulsive rats had lower levels of D2 and D3 receptors – molecules that interact with dopamine, a multi-purpose signalling molecule involved in feelings of pleasure.

Lab rats are telling us about how drug addiction happens in the brain.Dalley’s rats were given access to cocaine using a set-up that allowed them to give themselves a hit via a catheter. Sure enough, the impulsive rats gave themselves many more drug infusions than the non-impulsive ones.

So in rats at least, an individual’s impulsiveness, as indicated by the levels of D2 and D3 receptors in their ventral striatum, signposts an inbuilt vulnerability to drug abuse.

Dalley’s work support earlier studies in which mutant rats without any D2 receptors altogether became quickly and strongly addicted to cocaine. In rats, these receptors may act as a molecular conscience, limiting excessive reactions to addictive substances.

And once drug use begins, it triggers other changes in the way the striatum reacts to dopamine. Studies in monkeys have found that as the animals start getting hooked on cocaine, the levels of D2 receptors in their dorsal striatum – next to the ventral part – start to fall, and stay that way for years after they come off the drug.

These results provide a behind-the-scenes look at the molecular changes that turn an impulsive urge to take a drug to a compulsive urge to continue taking it.

It is likely that the receptors play a similar role in our own brains, and their levels are probably controlled by genetic variations. Finding the genes responsible could provide valuable clues for identifying ways of treating addiction, or preventing successful quitters for relapse.

And while cocaine was the drug of choice in this study, Dalley’s results could have implications for other drugs like nicotine (which is equally addictive), or possibly even non-pharmacological addictions like gambling.


Reference: Dalley, Fryer, Brichard, Robinson, Theobald, Laane, Pena, Murphy, Shah, Probst, Abakumova, Aigbirhio, Richards, Hong, Baron, Everitt & Robbins. 2007. Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. Science 315: 1267-1269.

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Brain parasite drives human culture

The brain parasite, Toxoplasma gondii, is spread by cats and affects a huge proportion of the world’s population. It’s effects on our behaviour make it a potent driving force of human culture.

Toxoplasma, a brain parasite that drives human cultureWe like to think that we are masters of our own fates. The thought that others might be instead controlling our actions makes us uneasy. We rail against nanny states, we react badly to media hype and we are appalled at the idea of brainwashing.

But words and images are not the only things that can affect our brains and thoughts. Other animals – parasites – can do this too.

Now, Kevin Lafferty from the University of California, Santa Barbara, has found startling evidence that a common brain parasite, Toxoplasma gondii, could be influencing human culture across the globe.

Toxoplasma gondii is a single-celled brain parasite spread by cats. Our feline companions are its preferred home and only there can it mature and reproduce. So like most parasites, T.gondii has a complex life cycle designed to get it into its final host.

If it finds itself in another animal, it travels to the brain and changes the host’s behaviour to maximise its chances of ending up in a cat. For rodents, this means being eaten and infected individuals are less fearful of cats and more active, making them easier prey.

Humans can become infected with Toxoplasma after contact with cats. Humans can also contract the parasite, through contact with soil contaminated by the faeces of carriers or through eating infected meat. But since cats are very unlikely to eat humans, in our bodies, T.gondii reaches a cul-de-sac. Still, there is nothing to stop the parasite, evolutionarily speaking, from trying out the strategies that work so well in other hosts.

In rare cases, T.gondii infection causes a disease called toxoplasmosis that produces mild flu-like symptoms and only really threatens foetuses and those with weak immune systems. In most instances, the parasite acts more subtly.

Carriers tend to show long-term personality changes. Women tend to be more intelligent, affectionate, social and more likely to stick to rules. Men on the other hand tend to be less intelligent, but are more loyal, frugal and mild-tempered. The one trait that carriers of both genders share is a higher level of neuroticism – they are more prone to guilt, self-doubt and insecurity.

In individuals cases, these effects may seem quirky or even charming but across populations, they can have a global power. T.gondii infection is extremely common and rates vary greatly from country to country.

While only 7% of Brits carry the parasite, a much larger 67% of Brazilians are infected. Given that the parasite alters behaviour, infection on this scale could lead to sizeable differences in the general personalities of people of different nationalities. This is exactly what Lafferty found.

Neuroticism is one of the most widely-studied of all psychological traits and Lafferty found that levels in different countries correlated well with the levels of T.gondii infection. The parasites’ presence was also related to aspects of culture associated with neuroticism.

Countries where infection was common were more likely to have ‘masculine sex roles’, characterized by greater differences between the sexes and their part in society and a stronger focus on work, ambition and money rather than people and relationships. Strongly infected societies were also more likely to avoid risk and embrace strict rules and regulations.

Obviously, different countries are also not just uniform populations, and increasing rates of migration mean that many countries are very ethnically and culturally mixed. However, this works in favour of Lafferty’s theory as any mixing would serve to mask the link between infection and culture. If anything, the link is stronger than seen in this study.

It would be imprudent to suggest that T.gondii is the major driver of human culture. It is just one of a number of influences that include genes, our physical environment and our histories. And Lafferty himself is quick to point out caveats to his own results.

For a start, they do not imply that the parasite is causing these personality types; it could be that people with these traits are more likely to become infected. To establish the true direction of causality, Lafferty will need to find out how the parasite manipulates the mind. The general idea is that infection alters levels of the immune system’s communication chemicals – the cytokines – which in turn alter levels of neurotransmitters like dopamine. But the details remain a mystery.

Nonetheless, the results are striking and they suggest that climate could have a larger effect on culture than previously thought. Toxoplasma gondii’s eggs live longer in humid, low regions so variations in climate could influence the global distribution of cultural traits. Perhaps, this could explain why men and women perform more distinct roles in society in countries in warmer climates. Other factors can also affect the risk of infection, including cat ownership and national cuisines that include undercooked meat.

We like to think of culture as something governed by the collective actions of free-thinking and free-acting humans. But Lafferty’s analysis shows us that if environmental factors like parasites can affect our thoughts and actions, no matter how subtly, they can have a strong effect on national cultures.

In many cases, these effects could be much stronger than the agents that we normally believe to drive cultural trends. After all, more people around the world are infected with Toxoplasma than are connected to the internet.

Reference: Lafferty. 2006. Proc Roy Soc B 273: 2749 – 2755.

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Related posts on other parasites:

Worms track us down with a chemical trail
Genetically-modified mosquitoes fight malaria by outcompeting normal ones

Parasites can change the balance of entire communities

Viruses evolve to be more infectious in a well-connected population
The secret of drug-resistant bubonic plague