To Worry or Not To Worry: How Stress Strengthens Memories

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Stress is a common experience that often garners a negative reputation. Most of us associate stress with lowering our abilities to perform everyday tasks and increasing our chance of errors. Previous neuroscience research generally agrees that stress negatively impacts our cognitive abilities, such as learning and memory, which are associated with a critical brain region called the hippocampus. However, these studies have also discovered an interesting conundrum: we seem to remember emotionally charged memories better under stressful conditions. “A lot of previous research has instead focused on the ways in which stress-related emotional memory enhancements can be explained by other brain regions, such as the amygdala,” said Brynn E. Sherman GSAS ’22, a Yale PhD graduate in psychology. 

A recent study by Sherman and colleagues shed light on the underlying mechanisms within the hippocampus that enable stress to enhance memories involving emotional information. In the experiments, participants were given either a placebo or hydrocortisone pill, the latter of which contained cortisol, a key hormone involved in stress. Subsequently, participants were shown pictures of household (neutral) or alcohol-related (emotional) objects on various backgrounds while in an MRI scanner, which recorded brain activity using functional magnetic resonance imaging (fMRI). The next day, participants were tested on their memories of the objects and object-background pairings. “One notable thing about this study is that we used a double-blind, placebo-controlled design… meaning that neither the participants nor the experimenter knew which pill was which,” Sherman said. This design allowed the study to randomize the order of administering cortisol and strictly control for potential confounding effects that may arise in similar investigations.

The findings were telling: cortisol significantly increased connectivity within subareas of the hippocampus compared to the placebo. Moreover, such connectivity led to enhancements in emotional memories under cortisol. “This enhancement was specific to the hippocampal circuit; amygdala-hippocampal connectivity was not altered by hydrocortisone,” the researchers concluded in their paper. “A lot of previous research has focused on how stress hurts the hippocampus. In the current study, though, we show that stress can have positive effects on the hippocampus, which can explain some of the benefits for emotional memory under stress,” Sherman said. Additionally, alcohol-related images, which can induce both positive and negative emotions, allowed the researchers to hypothesize that positive emotions can strengthen memories, not just negative ones that have been extensively examined by prior studies.  

Looking ahead, there are still many questions to be answered before we can fully understand the relationship between stress and memory. “The hippocampus is typically thought of as supporting episodic memory, which is our ability to form a distinct memory for a unique experience. But the hippocampus also supports a few other kinds of memory, including a type of memory called statistical learning, which is our ability to form links across related memories,” Sherman said. “I’m really interested in extending this out and understanding how stress impacts different kinds of memory that are supported by the hippocampus.”