Ever tried showing a porn film to someone who is lying in a brain scanner? It’s not easy. First, the scanner contains a powerful magnet that will drag anything that’s metallic and not properly bolted down – including bits of TVs – into it at high speed. Even if that doesn’t happen, the magnetic force might play havoc with the electronics. Then there’s the noise. MRI scanners aren’t exactly quiet. The intrusive humming and banging noises would undoubtedly be a distraction to anyone trying to get in the mood. To make matters worse, the volunteer has to lie perfectly motionless for you to be able to get a clear image of their brain. All in all, it’s not conducive to a happy viewing experience.


But at Northwestern University in Illinois, they have managed to overcome these practical difficulties. The erotic movies, downloaded from the internet or on DVD, are played onto a screen behind the scanner from a projector that’s outside the room. The volunteer can watch the X-rated action using a mirror just above their eyes. To block out the din of the scanner, the volunteers wear headphones and the sounds they need to hear are relayed through those.

But the problems don’t end there. “In general we know that men are more interested in visual erotica,” says Adam Safron, a research consultant at the university. “It’s a more difficult task finding stimuli that women like to the same degree.”



These are the challenges faced by neurologists at Northwestern who are trying to understand what goes on in the brains of men and women when we have feelings of Lust. Their research is certainly unusual and reveals that we’re hard-wired to sin. The scans show that in both sexes, the evolutionarily ancient limbic system, buried deep inside our brains, fires up when we are watching something we take a fancy to. Structures like the nucleus accumbens, involved in pleasure and craving, are at the heart of that system. It’s the enjoyable face of sin. And there’s an obvious reason why we’d be hard-wired for lust – to pass on our genes. It’s in Mother Nature’s interest to encourage us to, erm… take an active interest in procreation.

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The reward circuitry in our brains also lights up when we eat. “We find these things rewarding because of the evolutionary logic – you want organisms to reproduce, you want them to eat.” But eating itself isn’t a bad thing. It’s only a problem when sustenance turns to gluttony. And even here it seems that we have nature to blame. “In the environment that we evolved in, food was more scarce – there were no cheesecakes and no hamburgers,” says Safron. “Throughout most of our history, life was very difficult and these were the conditions that shaped our brains – set the dials for how much we want these things or how rewarding we find them.”

So what was once a dial setting for self-preservation is now a dial setting for sin – and it’s more of a problem for some than others.

“Some people have their dials set to overdrive,” Safron continues. “They are too motivated to achieve certain things and it ends up being unhealthy in a modern lifestyle. That same biological predisposition would have made them well adapted organisms in the past.” Many of us, it seems, have been born a few centuries too late – that irresistible cheesecake-devouring impulse would have stood us in good stead in 4000BC.



Safron also believes sloth – or the tendency to do absolutely nothing – has its roots in our evolutionary past. “You never knew when your next big meal would be coming, so if you could, you’d rest. The calories you don’t burn in activity, you could use for growth processes or to repair your body.” So that’s it. Mother Nature has wired our brains for certain things to be pleasurable to maximise the chances we’ll pass on our genes.

But not all sins are pleasurable. Take envy for instance. Whether it’s a work colleague who has just won a promotion or a team-mate who has made it into the first team ahead of us, no-one actually enjoys that feeling.



But at the National Institute of Radiological Sciences in Japan, they’ve been deliberately provoking the green-eyed monster. A group of male volunteers were presented with descriptions of three people. One of them was a success: highly intelligent, they were flying through university and had the same goals in life as the volunteers. To really rub salt into the wounds, they were a real hit with the ladies and had a very attractive girlfriend. The second person was female – also intelligent and popular with the boys, but not really having the same goals in life as the volunteer. The third person, again a girl, was something of a loser – a mediocre, unpopular student. The same descriptions were handed to the female volunteers, although the sexes of the students described were reversed.

As they read these descriptions, the volunteers were hooked up to a brain scanner to show where most blood was flowing in their grey matter and thus which region was the most active. In all the volunteers, without exception, reading about the high-flier with the attractive partner provoked a reaction in the brain region known as the anterior cingulate cortex (ACC).

“This area of the brain is also involved in the processing of physical pain, so envy is a painful emotion,” says Hidehiko Takahashi, one of the researchers involved in last year’s study. So if envy hurts, why would Mother Nature be so cruel as to wire it into all our brains? The important message from the study, says Takahashi, is that there was the biggest response in the ACC when the volunteers and the students they were reading about had the same aims. “There’s a positive or constructive element to envy: it motivates us to improve our own performance. Or, if it’s difficult to beat your rival, another strategy is to change your goal or interests.” But envy does have a dark side. “It could also make us want something bad to happen to the other person. So it can induce immoral behaviour or even a criminal act.”



Pride too, it seems, has its positive side. At Montclair State University just outside New York City, they have been temporarily knocking out certain parts of the brain using transcranial magnetic stimulation (TMS). The idea is simple. 3 3 If you can stop a certain portion of the brain from working, you can find out what it does. So a magnetic coil is placed near the volunteer’s head, disrupting the firing of the brain cells, or neurons. Volunteers wear something that resembles a swimming cap with markings on it so a specific spot in their grey matter can be targeted.

Aim the coil around the forehead, so that the magnetic field hits the medial prefrontal cortex (MPC) at the front of the brain, and something interesting happens. “What we normally see, at least in your everyday American subjects, is a small sense of enhancement,” says Professor Julian Paul Keenan, director of Montclair’s neuroimaging lab. They think they are a little bit better than they are.” But TMS can switch that self-enhancement off. The words the participants use to describe themselves and their friends suddenly change. “Without brain stimulation, they are more likely to say, ‘I’m intelligent and my best friend is not.’” But with the coil switched on, pride is switched off – the vocabulary people use to describe themselves is much less flattering.

“We’ve just finished studying a phenomenon known as ‘over-claiming’, where people pretend to know things they don’t. I’ll give them a made-up word like ‘trianic’. They really think they know this term, even though it’s not a real one. They say ‘Oh yeah, I’ve seen that word before, it’s something to do with biology.”

Again, a little zap with the coil stops this in its tracks. Interestingly, Keenan’s work shows that self-deprecation originates in the same area, so it looks like it’s just arrogance – or pride – in disguise. “They’re just different sides of the same coin,” he says.

The research has moved on at Montclair. They are currently testing whether removing that pride by knocking out the MPC makes the volunteers a little more depressed – they simply fill out a depression score before and after the test. So far, it’s too early for results. “Others have found that people who don’t have this self-enhancement tend to be clinically depressed. So if you realise how fat you really are, it’s going to drag you down. If you see yourself as others see you, it tends not to be a good thing, so a little bit of ego is pretty good.”

Again we’re back to that same idea – moderation. “It’s a common theme in biology – not too much, not too little,” says Safron. But some people’s dial settings are set too high – at least for the modern world.

It would make sense then for us, the ‘civilised’ species on this planet, to have developed some kind of self-control to keep our most basic of instincts in check. In one experiment at the University of Montreal in Canada, male volunteers watched clips of erotic films as their brains were scanned. And the clips produced responses in the deep, primitive parts of the brain such as the amygdala – no surprises there, then. But when they were asked to mentally suppress their sexual arousal, two different parts of the brain sprang into life – their right superior frontal gyrus and the right anterior cingulate gyrus. These are both found in the frontal lobes, the part of the brain that makes humans human, leading to, among other things, self-awareness.



Studies of wrath paint a similar picture. Some rather brave scientists at the University of New South Wales in Australia hurled abuse at volunteers in a brain scanner to see what would happen when they got angry. In those who were brooding types, rather than those with a short fuse, the medial prefrontal cortex (again part of the frontal lobes) quickly fired into action. It’s a region involved in moderating behaviour.

“Some people are better at inhibiting their impulses than others,” says Safron. “Some people may have the same drive towards a particular kind of behaviour, but less frontal inhibition.” So in some of us, it seems, the primitive beast within is more likely to win out.

The choices we make in life are often the result of this conversation between the advanced and primitive regions of the brain. “These evolutionarily ancient parts of the brain are constantly interacting with the cortex – which has expanded more recently – to produce behaviour.” But, says Safron, the emotional part of the brain – the limbic system – and the advanced cortex need each other to work. “If you sever the connections, it becomes difficult for someone to regulate their behaviour.”

Nowhere has this been spelled out more clearly than in a study of psychopaths carried out at King’s College London. Last year, researchers used a powerful new scanning technique, diffusion tensor magnetic resonance imaging, to study the brain structure of nine criminals with convictions that included attempted murder, manslaughter and multiple rape with strangulation. It was found that the psychopaths had poorer connections between their amygdala (in the emotional, limbic part of the brain) and their prefrontal cortex than others of a similar age and IQ.



But haven’t we forgotten something here? Isn’t the way we behave supposed to be the result of nature and nurture – the influences that shape us as we grow up? Unfortunately, when it comes to greed, there are no brain studies to provide us with the answers. “The mechanics of greed may be more complicated,” says Safron. “Gluttony and lust – if anything could be influenced by biological predispositions, they are. We know for instance, there are neurochemicals that increase or decrease your libido. But there are some things that are universal, which aren’t necessarily innate, and greed may be one of those things. There could be an innate basis for greed, but because it seems to be more complex, it is probably more likely to be shaped by learning.”


So the degree to which it’s nature – the shaping hand of evolution – or nurture that encourages us to be bad depends on the sin. But when it comes to the simplest of desires – to eat and have sex – there’s no doubting what’s at the heart of them. “I heard it said that emotions are evolution’s executioners – they are what natural selection uses to make organisms successful at propagating their genes,” says Safron. We’re nature’s puppets – dancing to a pre-ordained tune that’s been reinforced through the generations. Now that’s a great excuse to demolish a cream cake if ever there was one.


Andy is a Senior Lecturer in Science Communication at the University of the West of England in Bristol, Programme Leader of the MSc in Science Communication and an award-winning journalist