Pain is obviously one of the most important symptoms with which doctors deal, but measuring its severity objectively is difficult. Some people turn a twinge into agony, while others raise not a murmur in the last extremities of torture. And it is universally accepted that a person’s psychological state or disposition has a profound effect on his perception of pain.

Philosophers, indeed, have used the phenomenon of pain to debate what seemed to them an important question, namely whether there were such things as private languages or inner states inaccessible to others.

Clever experiments reported in a recent issue of the New England Journal of Medicine offer the hope, perhaps illusory, that brain imaging techniques might one day distinguish between real and severe pain on the one hand from exaggerated or false pain on the other (people may exaggerate or lie about pain for a variety of reasons).