The Hidden Costs of Stress on Your Memory

New research shows how the experience of stress can erode your memory.

Posted Sep 10, 2019

When you’re stressed, it can be difficult to focus on the task at hand. All you can think about is how far behind you are in your work, how poorly your relationship is going, or whether you’ll be able to pay your utility bill or not. You spend your days preoccupied with the feeling of being overwhelmed by the challenges that face you. Stress begets stress as your inability to concentrate means that you’re more likely to make mistakes, further worsening the actual situation in which you find yourself. 

Theories of stress and coping emphasize the cognitive components of the negative emotions that can stymie you in overcoming the challenges you face. Stress, in this view, is in the mind of the beholder. It’s that belief in your inability to conquer challenges that leads to the negative emotions of anxiety and worry. If you can perceive the threatening situation as a challenge (“I’ll be able to pay that bill by cutting expenses elsewhere”) then the stress will dissipate and positive emotions will replace it.

All of this takes a great deal of mental effort, which theoretically can detract from your ability to perform cognitively challenging tasks. However, according to University of Greifswald (Germany) psychologist Janine Wirker and colleagues (2019), there may be ways in which your memory can actually be enhanced in tasks that tap your ability to recall emotionally-arousing stimuli. Frightening events trigger a rise in the activity of the amygdala, the fear-sensing part of the brain. The amygdala, Wirker and co-authors note, is “the center of a widespread salience network”—meaning that once fired up, it promotes “hypervigilance towards potentially threatening stimuli” (p. 93). Your increased attention to these emotionally arousing events leads to enhanced memory in the all-important encoding stage that registers new information.

If, perhaps, acute stress helps your memory for emotionally arousing stimuli, what happens when the stress is constant? You might notice, and therefore remember, emotionally jolting events, but can your preoccupation with the problems in your life drain your mental resources for the ordinary details required for performing more mundane everyday tasks?

Wirker et al. note that the findings are not clear-cut with regard to the effects of chronic stress on memory in humans. Lab studies with rats clearly show that there are detrimental long-term effects of being placed under experimentally-induced chronic stress. These effects include actual degeneration of neurons in the brain region responsible for memory and a slower rate of recovery from that damage. Researchers who study stress and long-term memory in humans assume that there are similar effects, but as Wirker et al. note, the results are less consistent.

Rather than induce chronic stress in their human participants, the German researchers measured levels of existing stress by examining the amount of cortisol in the hair, a hormone that lodges in your follicles, registering exposure to stress over the past six months. Wirker and her colleagues then exposed their participants to photographs found in previous research to evoke strong emotional reactions. The positively arousing pictures included erotic couples and adventure; negatively arousing photos showed scenes involving attack and mutilation. As control, other photos of a neutral emotional quality included images of nature and objects.

The authors predicted that participants with high levels of cortisol in their hair would be more likely to attend to the emotionally-laden pictures due to their heightened state of alertness to any potential threats. The sample consisted of 20 healthy women with an average age of 21, screened for history of psychological disorders, current or chronic medical conditions, and familiarity with the actual stimulus materials. In addition to testing their memory for the pictures, the research team also took electrophysiological measurements consisting of what is called a “late positive potential (LPP),” which provides an indication of attentiveness and is tied to functioning of that fear-sensing amygdala.

In evaluating memory, the authors used a measure of recognition memory, in which participants stated whether they had seen the photograph or not (i.e. “Yes-No”). Recognition memory tests offer the distinct advantage for this type of study by providing researchers with an indication of whether participants are trying to improve their scores with “false alarm” responses in which they hedge their bets on getting the answer right by saying “yes” even when a stimulus was not actually shown to them. This rate, when compared with the “hit” rate (a “yes” response to an actual stimulus) allows researchers to test memory accuracy, or ability to discriminate the photos in the actual stimulus set. You can imagine that people primed to over-react to emotion-arousing pictures would probably have a high false alarm rate because they are just not that good at attending to details when their internal stress signals become triggered.

As the authors expected, those with high cortisol levels were especially likely to show greater LPP’s, hence brain activation, when confronted with emotional stimuli compared to neutral controls. Thus, people under chronic stress become hypervigilant to any new stimulus that has emotional significance.

You can probably relate to this experience if you’ve ever felt particularly stressed for a period of time and have become chronically edgy. You’re sitting outside in the fresh air trying to relax and get your mind off of work. All of a sudden, you catch sight of a car going down the street at what you think is an excessive rate of speed. You feel your blood pressure rise as you worry that the car is going to hit a pedestrian. As it turns out, the car just goes by, but you remain quite rattled.

Turning now to memory, you might think that the heightened attention the stressed participants paid to emotional stimuli would actually help them solidify their memory for the stimuli they saw in the lab. However, supporting animal models of stress and memory, the participants with higher stress levels performed less accurately when tested on emotional stimuli. They also had higher false alarm rates.

Thus, people under chronic stress may pay undue attention to new stimuli but then become primed to believe they saw images that were never presented to them. The anxiety that can accompany these constant shocks to the system could contribute, as the authors suggest, to the development of the stress-related psychological disorders involving alterations in mood and anxiety as well as to poorer memory overall.

To sum up, the German study shows the value of recognizing the potential for constantly high stress levels to impair not only your mental health but also your ability to function cognitively in the world. Working that cortisol out of your hair as well as your body’s inner functioning can help you retain both your memory and your peace of mind.

References

Wirkner, J., Ventura-Bort, C., Schwabe, L., Hamm, A. O., & Weymar, M. (2019). Chronic stress and emotion: Differential effects on attentional processing and recognition memory. Psychoneuroendocrinology, 107, 93–97. doi: 10.1016/j.psyneuen.2019.05.008