Particularly Exciting Experiments in Psychology

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February 26, 2015

How Does Stress Influence Behavior?

illustration of man pulling out his hairIn a recent poll of 2,500 Americans from across the country, 49% said that they had "a major stressful event or experience in the past year". Stress can contribute to health problems such as headaches, high blood pressure, heart problems, and skin conditions. Stress may also influence cognitive processes because it is associated with elevated levels of cortisol, a hormone that can influence brain functioning.

Of course, experimenters can't recreate real-life stressors in the lab. Instead, they induce a laboratory analog such as cold pressor stress (CPS) where participants submerge their non-dominant arm in ice-cold water. This causes a painful sensation and elevates cortisol levels. Control participants submerge their arm in warm water, which does not produce these effects.

Hupbach and Dorskind (2014, Behavioral Neuroscience) (PDF, 118KB) used CPS to test effects of stress on reactivated memories.

In Session 1, participants saw alternating pictures of animals and objects, and were told to remember the objects. The same pictures were shown 6 times in a pseudo-random order, such that a particular object always followed a particular animal (e.g., dog was always presented before bike).

In Session 2, participants made land/water judgments about a series of animal images. Critically, some of the animal images were the same as those shown in Session 1, and were therefore expected to reactivate memory for the associated object (e.g., dog should reactivate bike). Next, participants were exposed to CPS or the control treatment.

In Session 3, participants listed all the objects they could remember from Session 1.

In the control group, reactivated objects were remembered better than objects that were not reactivated. However, this benefit for reactivated items was absent in the stress group. Moreover, the stress and control groups differed in memory for reactivated objects, but did not differ in memory for non-reactivated objects, suggesting that stress selectively impaired memory for reactivated items.

Hupbach and Dorskind found that stress influenced cognitive processing over which participants did not have conscious control. But stress may also change overt behavior. For example, Pool and colleagues (2015, Journal of Experimental Psychology: Animal Learning and Cognition) (PDF, 260KB) examined the influence of stress on reward pursuit.

In Phase 1, geometric shapes were presented one at a time. Participants were told that squeezing a handgrip during "special" 1-second windows would trigger a chocolate odor. They could choose when to squeeze the handgrip, and were encouraged to rely on their intuition.

In Phase 2, one of the geometric shapes was associated with the chocolate odor via Pavlovian conditioning. After Phase 2, stress was induced in half the participants via CPS.

In Phase 3, the Phase 1 task was repeated.

All participants squeezed the handgrip more when the shape associated with the chocolate odor in Phase 2 was presented. However, this effect was larger in the stress group. That is, participants in the stress group made more squeezes to the stimulus associated with the chocolate odor than control participants, suggesting greater desire for the reward. Interestingly, the groups did not differ in their ratings of perceived pleasantness of the chocolate odor at the end of the experiment.

Thus, stressed participants worked harder to obtain the chocolate odor reward (i.e., greater wanting), even though they did not enjoy it more (i.e., equal liking). This dissociation of wanting and liking parallels a common observation after extended exposure to drugs of abuse.

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