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Talk of icy stares and dirty minds might be closer to the mark than we thought, says Jim Giles

“WILL these hands ne’er be clean?” asks Lady Macbeth, as she obsessively tries to wash away the guilt she feels for her role in the murder of King Duncan. Her feelings of self-disgust, we are led to believe, have manifested themselves as a sensation of physical dirtiness.

It is not only in the language of playwrights such as Shakespeare that complex emotions like guilt, grief or loneliness are compared to physical sensations. These metaphors crop up in everyday phrases, too, in many languages. In English, for example, we talk of being “left out in the cold” when we feel socially excluded, a sentiment echoed in the Japanese saying “one kind word can warm three winter months”.

At face value, these connections seem purely symbolic. In real life, loneliness doesn’t really send us shivering, and guilt doesn’t really make us feel dirty. Or do they? Recent research has found that these physical sensations can often accompany our emotions. It works the other way too – by provoking a feeling of disgust, a scene from the film shaped the way subjects in an experiment made moral judgements.

Many now believe that this reflects the way complex emotions arose in our evolutionary past. As our brain evolved to process more and more complex emotions, the theory goes, there was no need for new neural machinery: our emotions simply piggybacked onto the circuits that handle basic sensory perceptions. Here are some of the most striking experiments linking physical sensations with emotions and behaviour.

Cold shoulders and warm receptions

DURING the autumn of 2006, a series of volunteers arrived at Yale University’s psychology building. Each was greeted in the lobby by a researcher, who accompanied them up to the fourth floor. In the elevator, the researcher casually asked the volunteer to hold the drink she was carrying while she noted down their name. The subjects did not know it, but the experiment began the moment they took the cup.

Once in the lab, the 40 or so volunteers read a description of a fictitious person and then answered questions about the character. Those who had held an iced coffee, rather than a hot one, rated the imaginary figure as less warm and friendly, even though each volunteer had read the same description. Answers to other questions about the figure, such as whether the character appeared honest, were unaffected by the type of drink ( Science , vol 322, p 606 ).

The experiment, run by Lawrence Williams of the University of Colorado at Boulder and John Bargh of Yale, is not the only study to link physical and psychological warmth. Just thinking about being socially excluded, for example, can make the room feel around 3 °C cooler ( Psychological Science , vol 19, p 838 ). This may explain some aspects of how we socialise. For example, it is more common to offer a hot drink rather than a cold one when we welcome someone into our home.

“Certain behaviours people engage in during interpersonal relationships reflect an understanding of the link between physical and psychological warmth,” says Williams.

The insular cortex, which lies deep within one of the folds that line the surface of the brain, is probably at the root of these results. Brain imaging shows that this area is active when people are experiencing both physical and psychological warmth. The connection is probably present at birth and strengthened during early life, when babies learn to associate the physical warmth of their parents with nourishment and protection, says Williams.

Cleanliness and godliness

“TRULY Allah loveth those who turn unto Him, and loveth those who have a care for cleanness,” says the Koran. Islam is not alone in linking hygiene to moral purity. Christians cleanse the body and soul through baptism, and cleanliness is likewise important to Hindus.

This connection, which is entrenched in the orbitofrontal cortex of the brain, can have a profound and unexpected influence on our behaviour. In one recent study, Simone Schnall at the University of Plymouth, UK, and colleagues showed half their volunteers a neutral film and the other half the toilet scene from the film Trainspotting . (The uninitiated need only use their imagination here: the clip features what is described as the “worst toilet in Scotland”.) Those who viewed the Trainspotting clip subsequently made more severe judgements about unethical acts such as cannibalism than volunteers who had viewed the neutral scene. Exposing subjects to a fart smell and placing them in a filthy room had a similar effect (Personality and Social Psychology Bulletin , vol 34, p 1096 ).

And as Lady Macbeth’s obsessive hand-washing suggests, a feeling of guilt can leave us reaching for a bar of soap. Chen-Bo Zhong of the University of Toronto in Canada and Katie Liljenquist, now at Brigham Young University in Provo, Utah, asked volunteers to read a first-person account of either an ethical act or an act of sabotage. They then had to rate the desirability of various household objects, including soap, toothpaste, CD cases and chocolate bars. Those who had read the sabotage story showed a greater preference for the cleaning products (Science vol 313, p 1451 ) than those who had not.

A simplistic conclusion from these experiments would be that a cleaner environment makes us more tolerant of the misdemeanours of others. Yet the act of physical cleansing does not necessarily encourage us to act more morally ourselves, as religious ceremonies might have us believe. In another part of their study, Zhong’s team asked volunteers to recall an unethical deed from their past. Under the guise of a health and safety precaution, he then gave half the subjects antiseptic wipes to clean their hands. The participants were then asked if they would take part in another experiment, this time to help out a desperate graduate student. Only 40 per cent of the subjects who had cleaned their hands volunteered, compared with almost three-quarters of those who hadn’t.

Other experiments have shown that feelings of moral disgust can spur people to help others. By allowing people to wash away these feelings, say Zhong and Liljenquist, we may be giving licence to ungenerous behaviour.

The sting of rejection

CAST your mind back to your schooldays. Do you remember how it hurt when you were left out of a game? Or how you felt when you weren’t invited to a party? The pain of exclusion may seem tangible, but can it ever resemble the sensation of a physical wound?

To probe the neural link between physical and emotional pain, Naomi Eisenberger at the University of California, Los Angeles, and colleagues asked volunteers to play a virtual ball game. Each volunteer believed that their teammates were in other labs, but in fact these “people” were generated by the software, which was also programmed to gradually exclude the human player. All the while an fMRI scanner recorded the subject’s neural activity.

The scans revealed that the feelings of social exclusion increased activity in the dorsal anterior cingulate cortex (dACC), an area of the brain also involved in the feelings of distress that accompany physical pain. The dACC also lit up when people thought about the death of a loved one (Science , vol 323, p 890 ).

This might explain why some people in deep emotional pain turn to drugs like alcohol or heroin, which numb physical pain. Yet according to an unpublished study by Nathan DeWall at the University of Kentucky in Lexington, less potent drugs could also do the trick, without side effects.

DeWall asked around 60 college students to take either paracetamol (acetaminophen) or a placebo in the morning and evening for three weeks. The students also answered daily questions about their emotional state. DeWall found that those who took the painkiller reported fewer hurt feelings.

In another experiment, DeWall gave paracetamol or a placebo to volunteers playing the virtual ball game. The result was as expected: the painkiller reduced activity in the dACC that was associated with the emotionally painful feelings of exclusion. He now wants to test the drug on people with clinical symptoms of depression or anxiety. “Anxious people are constantly concerned about negative evaluation,” he says. “Perhaps Tylenol [paracetamol] can help them.” It remains a long shot, and not something to be recommended right now, but if the results pan out it will be an interesting avenue to explore for the future. ■

Jim Giles is a writer based in San Francisco

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