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Neuropsychopharmacology. 2017 Mar;42(4):801-810. doi: 10.1038/npp.2016.191. Epub 2016 Sep 13.

Lipopolysaccharide Alters Motivated Behavior in a Monetary Reward Task: a Randomized Trial.

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Division for Psychology, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
Stress Research Institute, Stockholm University, Stockholm, Sweden.
Institute of Medical Psychology and Behavioral Immunobiology, Universitätsklinikum Essen, Essen, Germany.
Department of Psychology, Emory University, Atlanta, GA, USA.
Division of Internal Medicine, Department of Symptom Research, The University of Texas, MD Anderson Cancer Center, Houston, TX, USA.
Department of Clinical Sciences, Danderyd Hospital, Karolinska Institutet, Stockholm, Sweden.
Osher Center for Integrative Medicine, Karolinska Institutet, Stockholm, Sweden.


Inflammation-induced sickness is associated with a large set of behavioral alterations; however, its motivational aspects remain poorly explored in humans. The present study assessed the effect of lipopolysaccharide (LPS) administration at a dose of 2 ng/kg of body weight on motivation in 21 healthy human subjects in a double-blinded, placebo (saline)-controlled, cross-over design. Incentive motivation and reward sensitivity were measured using the Effort Expenditure for Rewards Task (EEfRT), in which motivation for high-effort/high-reward trials vs low-effort/low-reward trials are manipulated by variations in reward magnitude and probability to win. Because of the strong interactions between sleepiness and motivation, the role of sleepiness was also determined. As expected, the probability to win predicted the choice to engage in high-effort/high-reward trials; however, this occurred at a greater extent after LPS than after saline administration. This effect was related to the level of sleepiness. Sleepiness increased motivation to choose the high-effort/high-reward mode of response, but only when the probability to win was the highest. LPS had no effect on reward sensitivity either directly or via sleepiness. These results indicate that systemic inflammation induced by LPS administration causes motivational changes in young healthy subjects, which are associated with sleepiness. Thus, despite its association with energy-saving behaviors, sickness allows increased incentive motivation when the effort is deemed worthwhile.

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