By Althea Need Kaminske

Cover image by Mizuno K from Pexels

Recently, Cindy talked about how the Yerkes-Dodson Law (or performance-arousal) is less of a law and more of a nice story about how stress influences performance. The performance-arousal curve is a handy explanation for a lot of different patterns and, on the surface, it seems to tell an interesting story about how stress affects our performance. Further complicating the story, the label of Yerkes-Dodson Law itself is incorrect. The performance arousal curve was developed independently of the results of the Yerkes-Dodson experiments, some 50 years later. This curve that is typically shown when talking about Yerkes-Dodson later conflated with Yerkes-Dodson and could more appropriately be called the Hebbian performance-arousal curve (1).

This is a lot to take in. Reader, I was shocked. I was shook. I have taught this “law” as part of my classes for the last decade. I was also more than a little embarrassed and slightly horrified that I had passed on bad information to my students without question. But, one of the joys of science is being wrong! If something is important enough for me to examine and think critically about, then I have to be open to being wrong about it. As uncomfortable as it is to find out you were wrong, I ultimately believe that it’s better to care enough to find out, than to not. (The ability to be ok with being wrong is, as it turns out, an important component of critical thinking (2)). And, ultimately, this led to a series of other questions for me to investigate. One of which was “Well, then how does stress affect memory?”

“Fight-or-flight”

When we are presented with a stressful event, a variety of hormones, neurotransmitters, and peptides are released in our brains. All of these things work to activate systems to help us cope with the stressor. This initial response is typically referred to as the “fight-or-flight” response. If you were walking in the woods and actually saw three bears your fight-or-flight response would put your system on high-alert. Your body diverts resources from less-pressing matters, like digestion, and focuses on giving you superhuman strength and speed. Your heart rate goes up as blood is pumped to muscles, your blood sugar goes up as your body creates more fuel, and your breathing rate increases as you burn that fuel. Your muscle tension is increased and your pupils dilate so you can take in more visual information. You’re primed and ready to fight or take flight (Note: The U.S. National Parks Service does not advise fighting bears. Nor do they advise running away from bears. You should calmly identify yourself, pick up any small children, and back away slowly  https://www.nps.gov/subjects/bears/safety.htm ). This response is not always useful. 

While your body is being primed to fight or flee, your mind is being primed to assess and remember. Your attention for emotionally-salient information is increased and stressor-irrelevant information is decreased, making you laser-focused on the stressor (3). Afterwards, you are primed to store stressor-relevant information to improve coping with something similar in the future (1,3). If you come across three bears on your hike you’re probably not going to remember much about the hike that was not directly relevant to those bears. And you’re going to remember MUCH more about those bears than if you had encountered them under different circumstances, like at a zoo. Your brain helps to keep you alive by doing everything in its power to say “We might die. Let’s pay close attention and make sure we don’t do THAT again.”

Similar to how our “fight-or-flight” response diverts energy and resources from some body functions (i.e. digestion), there is evidence that a similar phenomenon happens with cognitive functions. We rely less on reflective, “cognitive” based systems and rely more on reflexive, “habit” based systems. When we are stressed it is easier to fall back on habits and routines, and harder to engage in critical thinking and developing new thought patterns.

Taken as a whole this paints a more nuanced picture of how stress affects memory. When we experience a stressful event our memory is improved for whatever was stressing us out. So in this way our memory is improved. However, we are less able to pay attention to and remember other aspects of the event, and have difficulty with critical thinking and learning new thought patterns. So, our learning for things that are not the stressful event are impaired. In the case of truly life-threatening scenarios, this is an adaptive response. If I encounter bears on my morning walk with my dog I will certainly avoid that area in the future! However, in the case of our more day-to-day experiences this may end up being maladaptive for us. This tendency can contribute to more extreme stress responses as is the case in post-traumatic stress disorder (PTSD) or anxiety disorders (1,4). In these cases our heightened memory for stressful events impairs our ability to function by forcing us to remember a traumatic event, or causing us to fall back on old habits.

References:

1. Diamond, D. M., Campbell, A. M., Park, C. R., Halonen, J., & Zoladz, P. R. (2007). The temporal dynamics model of emotional memory processing: A synthesis on the neurobiological basis of stress-induced amnesia, flashbulb and traumatic memories, and the Yerkes-Dodson law. Neural Plasticity. https://doi.org/10.1155/2007/60803

2. Halpern, D. F. (2014). Thought and knowledge: An introduction to critical thinking (5th ed.). Psychology Press.

3. Schwabe, L., Hermans, E. J., Joels, M., & Roozendaal, B. (2022). Mechanisms of memory under stress, Neuron, 110,1450-1464. https://doi.org/10.1016/j.neuron.2022.02.020 

4. Pitman, R. K., Rasmusson, A. M., Koenen, K. C., Shin, L. M., Orr, S. P., Gilbertson, M. W., Milad, M. R., & Liberson, I. (2012). Biological studies of post-traumatic stress disorder. Nature Reviews Neuroscience, 13, 769-787. https://doi.org/10.1038/nrn3339