W Gandhi1, S Becker, P Schweinhardt. 1. Alan Edwards Centre for Research on Pain (AECRP), McGill University, Montreal, Canada. wiebke.tiede@mail.mcgill.ca
Abstract
BACKGROUND: Pain and reward have been suggested to interact, and some evidence is provided by a rodent study showing that acutely injured animals are more motivated to reach a food reward while they do not increase food consumption, pointing at unaltered reward liking. Since no data exist in humans, we conducted a psychophysical experiment to test the effects of experimentally induced tonic pain on (1) the motivation to receive reward and (2) hedonic responses when being rewarded. METHODS: Forty healthy participants underwent two experimental sessions: in one, painful heat stimulation was continuously applied while participants played a monetary reward task; in the other, participants experienced non-painful warm stimulation while playing the task. In the task, participants needed to react quickly enough to a target cue to win the money associated with the particular trial ($0.04, $1 or $4). Reaction time to the target cue served as measure of motivation. Ratings after each trial on how much the participant liked the trial's outcome served as a measure of hedonic responses. RESULTS: Pain increased the motivation to obtain reward when the incentive was high, indexed by decreased reaction times (repeated-measures analysis of variance, interaction pain × incentive; p = 0.009). In contrast to motivational drive, hedonic ratings of the rewarding stimuli were not influenced by pain. CONCLUSION: Similar to existing rodent data, our results suggest a pain-induced mismatch of increased motivational drive with a lack of increased hedonic responses. This mismatch is discussed as perhaps reflecting a failed coping attempt, which is potentially relevant for chronic pain patients.
BACKGROUND:Pain and reward have been suggested to interact, and some evidence is provided by a rodent study showing that acutely injured animals are more motivated to reach a food reward while they do not increase food consumption, pointing at unaltered reward liking. Since no data exist in humans, we conducted a psychophysical experiment to test the effects of experimentally induced tonic pain on (1) the motivation to receive reward and (2) hedonic responses when being rewarded. METHODS: Forty healthy participants underwent two experimental sessions: in one, painful heat stimulation was continuously applied while participants played a monetary reward task; in the other, participants experienced non-painful warm stimulation while playing the task. In the task, participants needed to react quickly enough to a target cue to win the money associated with the particular trial ($0.04, $1 or $4). Reaction time to the target cue served as measure of motivation. Ratings after each trial on how much the participant liked the trial's outcome served as a measure of hedonic responses. RESULTS:Pain increased the motivation to obtain reward when the incentive was high, indexed by decreased reaction times (repeated-measures analysis of variance, interaction pain × incentive; p = 0.009). In contrast to motivational drive, hedonic ratings of the rewarding stimuli were not influenced by pain. CONCLUSION: Similar to existing rodent data, our results suggest a pain-induced mismatch of increased motivational drive with a lack of increased hedonic responses. This mismatch is discussed as perhaps reflecting a failed coping attempt, which is potentially relevant for chronic painpatients.