Stress makes us work harder for pleasurable rewards, but doesn't make us appreciate them more

 A new study from researchers at the University of Geneva suggests that while stress can cause us to work very, very hard to achieve rewards, being stressed out doesn't help us enjoy those rewards.
Specifically, the study helps shed light on why stress can often lead to binge-eating, relapses in alcoholism and drug addiction, or gambling.
"Most of us have experienced stress that increases our craving for rewarding experiences, such as eating a tasty bar of chocolate, and it can make us invest considerable effort in obtaining the object of our desire, such as running to a convenience store in the middle of the night," said the study's lead author Eva Pool, MS, a doctoral student at the University of Geneva. "But while stress increases our desire to indulge in rewards, it does not necessarily increase the enjoyment we experience."
From the study announcement:

Stress prompted chocolate lovers in an experiment to exert three times as much effort to smell chocolate than unstressed chocolate lovers, but both groups reported about the same level of enjoyment when they got a whiff of the pleasing aroma, according to the study, published in APA's Journal of Experimental Psychology: Animal Learning and Cognition.
For the experiment, researchers recruited 36 university students, of whom 19 were men, who said they love chocolate. To induce stress, the researchers asked students to keep one hand in ice-cold water while being observed and videotaped. Another group immersed a hand in lukewarm water. Ten minutes before and 30 minutes after the task, researchers collected samples of the participants' saliva and tested them for levels of cortisol, a hormone involved in stress response. Following the stress conditioning, all participants had to press a handgrip for the chance to smell chocolate when they saw a certain symbol. The researchers measured the amount of effort participants invested for a chance to smell the chocolate, and asked participants how pleasant they found the odor.
"Stress plays a critical role in many psychological disorders and is one of the most important factors determining relapses in addiction, gambling and binge eating," said another author, Tobias Brosch, PhD, also of the University of Geneva. "Stress seems to flip a switch in our functioning: If a stressed person encounters an image or a sound associated with a pleasant object, this may drive them to invest an inordinate amount of effort to obtain it."

Here's the summary from the report:

Stress can increase reward pursuits: This has traditionally been seen as an attempt to relieve negative affect through the hedonic properties of a reward. However, reward pursuit is not always proportional to the pleasure experienced, because reward processing involves distinct components, including the motivation to obtain a reward (i.e., wanting) and the hedonic pleasure during the reward consumption (i.e., liking). Research conducted on rodents demonstrates that stress might directly amplify the cue-triggered wanting, suggesting that under stress wanting can be independent from liking. Here, we aimed to test whether a similar mechanism exists in humans. We used analog of a Pavlovian-Instrumental Transfer test (PIT) with an olfactory reward to measure the cue triggered wanting for a reward but also the sensory hedonic liking felt during the consumption of the same reward. The analog of a PIT procedure, in which participants learned to associate a neutral image and an instrumental action with a chocolate odor, was combined with either a stress-inducing or stress-free behavioral procedure. Results showed that compared with participants in the stress-free condition, those in the stress condition mobilized more effort in instrumental action when the reward-associated cue was displayed, even though they did not report the reward as being more pleasurable. These findings suggest that, in humans, stress selectively increases cue-triggered wanting, independently of the hedonic properties of the reward. Such a mechanism supports the novel explanation proposed by animal research as to why stress often produces cue-triggered bursts of binge eating, relapses in drug addiction, or gambling.

PDF: Stress Increases Cue-Triggered “Wanting” for Sweet Reward in Humans