Scientists have begun to look in a different way at how the brain creates the convictions that mould our relationships and inform our behaviour. Alok Jha reports

Belief can make people do the strangest things. At one level, it provides a moral framework, sets preferences and steers relationships. On another, it can be devastating. Belief can manifest itself as prejudice or persuade someone to blow up themselves and others in the name of a political cause.

"Belief has been a most powerful component of human nature that has somewhat been neglected," says Peter Halligan, a psychologist at Cardiff University. "But it has been capitalised on by marketing agents, politics and religion for the best part of two millennia."

That is changing. Once the preserve of philosophers alone, belief is quickly becoming the subject of choice for many psychologists and neuroscientists. Their goal is to create a neurological model of how beliefs are formed, how they affect people and what can manipulate them.

And the latest steps in the research might just help to understand a little more about why the world is so fraught with political and social tension. Matthew Lieberman, a psychologist at the University of California, recently showed how beliefs help people's brains categorise others and view objects as good or bad, largely unconsciously. He demonstrated that beliefs (in this case prejudice or fear) are most likely to be learned from the prevailing culture.

When Lieberman showed a group of people photographs of expressionless black faces, he was surprised to find that the amygdala - the brain's panic button - was triggered in almost two-thirds of cases. There was no difference in the response between black and white people.

The amygdala is responsible for the body's fight or flight response, setting off a chain of biological changes that prepare the body to respond to danger well before the brain is conscious of any threat. Lieberman suggests that people are likely to pick up on stereotypes, regardless of whether their family or community agrees with them.

The work, published last month in Nature Neuroscience, is the latest in a rapidly growing field of research called "social neuroscience", a wide arena which draws together psychologists, neuroscientists and anthropologists all studying the neural basis for the social interaction between humans.

Traditionally, cognitive neuroscientists focused on scanning the brains of people doing specific tasks such as eating or listening to music, while social psychologists and social scientists concentrated on groups of people and the interactions between them. To understand how the brain makes sense of the world, it was inevitable that these two groups would have to get together.

"In the West, most of our physical needs are provided for. We have a level of luxury and civilisation that is pretty much unparalleled," says Kathleen Taylor, a neuroscientist at Oxford University. "That leaves us with a lot more leisure and more space in our heads for thinking."

Beliefs and ideas therefore become our currency, says Taylor. Society is no longer a question of simple survival; it is about choice of companions and views, pressures, ideas, options and preferences.

"It is quite an exciting development but for people outside the field, a very obvious one," says Halligan.

Understanding belief is not a trivial task, even for the seemingly simplest of human interactions. Take a conversation between two people. When one talks, the other's brain is processing information through their auditory system at a phenomenal rate. That person's beliefs act as filters for the deluge of sensory information and guide the brain's response.

Lieberman's recent work echoed parts of earlier research by Joel Winston of the University of London's Wellcome Department of Imaging Neuroscience. Winston found that when he presented people with pictures of faces and asked them to rate the trustworthiness of each, the amygdalas showed a greater response to pictures of people who were specifically chosen to represent untrustworthiness. And it did not matter what each person actually said about the pictured faces.

"Even people who believe to their core that they do not have prejudices may still have negative associations that are not conscious," says Lieberman.

Beliefs also provide stability. When a new piece of sensory information comes in, it is assessed against these knowledge units before the brain works out whether or not it should be incorporated. People do it when they test the credibility of a politician or hear about a paranormal event.

Physically speaking, then, how does a belief exist in the brain? "My own position is to think of beliefs and memories as very similar," says Taylor. Memories are formed in the brain as networks of neurons that fire when stimulated by an event. The more times the network is employed, the more it fires and the stronger the memory becomes.

Halligan says that belief takes the concept of memory a step further. "A belief is a mental architecture of how we interpret the world," he says. "We have lots of fluid things moving by - perceptions and so forth - but at the level of who our friends are and so on, those things are consolidated in crystallised knowledge units. If we did not have those, every time we woke up, how would we know who we are?"

These knowledge units help to assess threats - via the amygdala - based on experience. Ralph Adolphs, a neurologist at the University of Iowa, found that if the amygdala was damaged, the ability of a person to recognise expressions of fear was impaired. A separate study by Adolphs with Simon Baron-Cohen at Cambridge University showed that amygdala damage had a bigger negative impact on the brain's ability to recognise social emotions, while more basic emotions seemed unaffected.

This work on the amygdala shows it is a key part of the threat-assessment response and, in no small part, in the formation of beliefs. Damage to this alarm bell - and subsequent inability to judge when a situation might be dangerous - can be life-threatening. In hunter-gatherer days, beliefs may have been fundamental to human survival.

Neuroscientists have long looked at brains that do not function properly to understand how healthy ones work. Researchers of belief formation do the same thing, albeit with a twist. "You look at people who have delusions," says Halligan. "The assumption is that a delusion is a false belief. That is saying that the content of it is wrong, but it still has the construct of a belief."

In people suffering from prosopagnosia, for example, parts of the brain are damaged so that the person can no longer recognise faces. In the Cotard delusion, people believe they are dead. Fregoli delusion is the belief that the sufferer is constantly being followed around by people in disguise. Capgras' delusion, named after its discoverer, the French psychiatrist Jean Marie Joseph Capgras, is a belief that someone emotionally close has been replaced by an identical impostor.

Until recently, these conditions were regarded as psychiatric problems. But closer study reveals that, in the case of Capgras' delusion for example, a significant proportion of sufferers had lesions in their brain, typically in the right hemisphere.

"There are studies indicating that some people who have suffered brain damage retain some of their religious or political beliefs," says Halligan. "That's interesting because whatever beliefs are, they must be held in memory."

Another route to understanding how beliefs form is to look at how they can be manipulated. In her book on the history of brainwashing, Taylor describes how everyone from the Chinese thought reform camps of the last century to religious cults have used systematic methods to persuade people to change their ideas, sometimes radically.

The first step is to isolate a person and control what information they receive. Their former beliefs need to be challenged by creating uncertainty. New messages need to be repeated endlessly. And the whole thing needs to be done in a pressured, emotional environment.

"Beliefs are mental objects in the sense that they are embedded in the brain," says Taylor. "If you challenge them by contradiction, or just by cutting them off from the stimuli that make you think about them, then they are going to weaken slightly. If that is combined with very strong reinforcement of new beliefs, then you're going to get a shift in emphasis from one to the other."

The mechanism Taylor describes is similar to the way the brain learns normally. In brainwashing though, the new beliefs are inserted through a much more intensified version of that process.

This manipulation of belief happens every day. Politics is a fertile arena, especially in times of anxiety.

"Stress affects the brain such that it makes people more likely to fall back on things they know well - stereotypes and simple ways of thinking," says Taylor.

"It is very easy to want to do that when everything you hold dear is being challenged. In a sense, it was after 9/11."

The stress of the terror attacks on the US in 2001 changed the way many Americans viewed the world, and Taylor argues that it left the population open to tricks of belief manipulation. A recent survey, for example, found that more than half of Americans thought Iraqis were involved in the attacks, despite the fact that nobody had come out and said it.

This method of association uses the brain against itself. If an event stimulates two sets of neurons, then the links between them get stronger. If one of them activates, it is more likely that the second set will also fire. In the real world, those two memories may have little to do with each other, but in the brain, they get associated.

Taylor cites an example from a recent manifesto by the British National Party, which argues that asylum seekers have been dumped on Britain and that they should be made to clear up rubbish from the streets. "What they are trying to do is to link the notion of asylum seekers with all the negative emotions you get from reading about garbage, [but] they are not actually coming out and saying asylum seekers are garbage," she says.

The 9/11 attacks highlight another extreme in the power of beliefs. "Belief could drive people to agree to premeditate something like that in the full knowledge that they would all die," says Halligan of the hijacker pilots.

It is unlikely that beliefs as wide-ranging as justice, religion, prejudice or politics are simply waiting to be found in the brain as discrete networks of neurons, each encoding for something different. "There's probably a whole combination of things that go together," says Halligan.

And depending on the level of significance of a belief, there could be several networks at play. Someone with strong religious beliefs, for example, might find that they are more emotionally drawn into certain discussions because they have a large number of neural networks feeding into that belief.

"If you happen to have a predisposition, racism for example, then it may be that you see things in a certain way and you will explain it in a certain way," says Halligan.

He argues that the reductionist approach of social neuroscience will alter the way people study society. "If you are brain scanning, what are the implications for privacy in terms of knowing another's thoughts? And being able to use those, as some governments are implying, in terms of being able to detect terrorists and things like that," he says. "If you move down the line in terms of potential uses for these things, you have potential uses for education and for treatments being used as cognitive enhancers."

So far, social neuroscience has provided more questions than answers. Ralph Adolphs of the University of Iowa looked to the future in a review paper for Nature. "How can causal networks explain the many correlations between brain and behaviour that we are discovering? Can large-scale social behaviour, as studied by political science and economics, be understood by studying social cognition in individual subjects? Finally, what power will insights from cognitive neuroscience give us to influence social behaviour, and hence society? And to what extent would such pursuit be morally defensible?"

The answers to those questions may well shape people's understanding of what it really means to believe.