Try not to think about Freud - or polar bears

Our inability to suppress unwanted thoughts makes parties social minefields, and dooms our New Year's resolutions to failure.

A female polar bear (R) and her two two-year cubs stand at Cape Blossom on the Isle of Vrangel in this 2002 archive picture. Russia's polar bears are adapting their behaviour to overcome the "catastrophic effects" of global warming, but new migration routes are pushing them dangerously close to humans, a leading researcher said.  Picture taken in 2002.   REUTERS/International Fund for Animal Wellfare/Nikita Ovsyanikov  (RUSSIA ANIMALS ENVIRONMENT) NO SALES. NO ARCHIVES. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS *** Local Caption ***  MOS11_CLIMATE-RUSSI_1209_11.JPG

Here is a task for you. While reading this article, on no account think of your mother-in-law. If you do not have a mother-in-law, or actually enjoy thinking of your mother-in-law, substitute an object of disaffection: your boss, perhaps. The main thing is, whoever you choose, exclude them from your mind. Totally. Just do not think about them. Pretend they do not exist. Chances are you will fail, and that persona non grata will pop up on your mental doorstep. Suppressing unwanted thoughts is a strangely difficult thing to do, as Fyodor Dostoevsky trenchantly observed in his Winter Notes on Summer Impressions. "Try not to think of a polar bear," he challenged his readers, "and you will see that the cursed thing will come to mind every minute."

More alarmingly, the same goes for actions. Remind yourself not to tell the widow at the wake that you are dying for a drink, and as like as not, you will. Try not to spill the longed-for glass of camel's milk on that nice carpet: oops, there it goes. The harder you try to stop making a fool of yourself, the more likely it is that you will. It is as if a mischievous inner demon were constantly whispering to us to fulfil our worst desires - an imp dubbed "the counter will" by Sigmund Freud.

Spurred on by the observations of Dostoevsky and others, the Harvard psychologist Dan Wegner has spent considerable time investigating such "ironic" mental processes. "It was the kind of literary observation that turns into very good psychology," he says. He has a theory as to how ironic slips arise: they are the result of occasional errors in our sophisticated systems of mental control. It works like this. Say we have given up chocolate or cigarettes, and want to block all thoughts of them. We do this by filling our conscious mind with distracting thoughts - anything but chocolate or cigarettes. At the same time, though, our unconscious mind remains alert for any signs of the unwanted thought, the better to help us chase it away. "Some part of the mind has to know what it is we don't want to think about and to monitor for that," says Dr Wegner.

But the monitoring process also stores those unwanted thoughts as references in our unconscious, and that can come back to haunt us when our mind is under strain. That is because the conscious search for distractions involves a lot more mental effort than the unconscious monitoring process, making it much more prone to disruption by an extra mental load - when we are asked to multitask, for example, or when we simply try too hard to suppress an irksome thought (incidentally, you are really trying not to think of your mother-in-law, are you not?) That gives the unconscious thought the space to pop into our awareness with a vengeance. It is almost as if we have set a trigger for them, says Dr Wegner. "They become hyperaccessible."

A neat idea, but is there any evidence for it? In experiments in the 1990s, with Ralph Erber of DePaul University in Chicago, Dr Wegner tested the interplay of mental load and thought suppression. They found that undergraduates asked not to blurt out the word "house" while playing a word-association game involving related words, such as "home", performed significantly worse under time pressure. Think of the word "aunt" for a moment. You now have 10 seconds to name me 10 other sorts of familial relationship. Go!

The idea ties in, too, with the results of research by Thomas Pyszczynski of the University of Colorado and others into how we block out the most unwanted thought of all: death. Various suppression strategies - for example, clinging more strongly to things that seem to give life meaning, such as children or religious beliefs - seem to work well as long as our minds are not under stress. Add an extra mental load, however, and the naked fact of our own mortality starts to creep back in.

So what lessons can we take into the holiday season from this research? First, that it is a mental war zone. As the density of fraught social interactions increases, so does our mental load and our propensity for the social faux pas. Try thinking of one embarrassing thing you really ought not to say when visiting family and see how long it takes before it just slips out. The worst of it is that the more taboo a thought is, the more store we set by suppressing it and the more difficult it consequently becomes to contain. No surprise, then, that things get really messy when we are batting down our carnal desires. You might want to experiment with this on a friend - wait for an inappropriate moment, instruct them to keep their thoughts virtuous, then sit back and wait for their blushes, or a slap. * New Scientist