Expectation of pain replicates the effect of pain in a hand laterality recognition task: bias in information processing toward the painful side?

BACKGROUND People in pain, or expecting pain, sometimes bias their attention towards pain-relevant cues. Perhaps they also bias their attention towards the body part in question. AIM To determine if experimentally induced pain, and the expectation of pain, involve an information processing bias towards the hand in question. METHODS Seventeen asymptomatic subjects performed a hand laterality recognition task during three conditions: control, during hand pain induced by intramuscular injection of hypertonic saline (pain), and during expectation of hand pain, induced by isotonic saline injection (expectation). Mean response time (RT) was determined for three 45 s epochs within each condition and RT was compared between hands, conditions and epochs using a 2 x 3 x 3 repeated measures multivariate analysis of variance. RESULTS There was a hand x condition interaction and a hand x condition x epoch interaction (p<0.05 for both). RT to recognise the opposite hand was approximately 600 ms longer during epochs when subjects were in pain or expected pain than during control trials. During those epochs, RT to recognise the opposite hand was approximately 600 ms longer than RT to recognise the injected hand, which was consistent across conditions and across epochs. CONCLUSIONS Both pain and the expectation of pain increased RT to recognise the opposite hand. The findings are consistent with a bias in information processing toward the painful or impending painful hand.