Introduction: Although the motivation to avoid injury and pain is central to human and animal behavior, this goal compete priority with other homeostatic goals. Animal studies have shown that competing motivational states, such as thirst, reduce pain. However, such states may also induce negative mood, which in humans has been found to increase pain. These opposing effects complicate study of the effects of motivational states in humans.
Objectives: To evaluate concurrent effects of motivational state competition and mood on pain ratings.
Methods: We compared a thirst challenge against a control group and measured thirst and mood as potential mediators. Pain induced through contact heat stimulation on the left forearm and was tested at 3 time points: before group randomization, after thirst induction, and after rehydration.
Results: Overall, the thirst group reported more pain when thirsty compared with baseline and controls. Mediation analyses showed evidence for two opposing effects. First, the thirst challenge increased negative mood and thirstiness, which was related to increased pain. Second, the thirst challenge produced a direct, pain-reducing effect.
Conclusion: Competing motivational states reduce pain but also induce concurrent mood changes that can mask motivational state-related effects.
Competition for prioritization between basic motivational states, such as pain and thirst, is thought to inhibit the currently nonprioritized state. We show that thirst can reduce pain in humans, whereas at the same time enhance pain through increased negative mood.
aInstitute of Cognitive Science, University of Colorado Boulder, Boulder, CO, USA
bDepartment of Psychology and Neuroscience, University of Colorado Boulder, Boulder, CO, USA
Corresponding author. Address: Institute of Cognitive Science, University of Colorado Boulder, Boulder, CO, 80309. Tel.: +1 (303) 492-4299. E-mail address: email@example.com (S. Geuter).
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Received June 13, 2016
Received in revised form August 27, 2016
Accepted September 07, 2016