Yale scientists discover how stress changes the brain to make memories stronger
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Stress does more than influence how we feel. It can also change what we remember, particularly when an experience is emotionally intense or personally meaningful. Scientists have long known that cortisol, a hormone released during stressful situations, can strengthen emotional memories. What has been less clear is exactly how this happens inside the brain.
Researchers at Yale University have now uncovered important clues. Their study reveals that cortisol strengthens emotional memories by changing how brain networks involved in emotion and memory function and communicate with one another. The findings offer a deeper understanding of why certain experiences leave such powerful impressions while others quickly fade.
“We all experience stress, and my lab is interested in understanding how stress can be helpful,” said corresponding author Elizabeth Goldfarb, an assistant professor of psychiatry at Yale School of Medicine and of psychology in the Faculty of Arts and Sciences.
The findings were published in the journal Science Advances.
How Stress Hormones Influence Memory
Previous research involving both humans and rodents has shown that stress and cortisol can improve memory for emotional events. Scientists also know that certain brain regions, including the amygdala, play an essential role in this process. The amygdala is particularly important for processing emotions and identifying experiences that may be significant.
However, understanding precisely how cortisol strengthens memories has been challenging. Many brain regions participate in several mental functions, making it difficult to determine whether the hormone is influencing emotional responses, memory formation, or both.
“Forming memories for emotional experiences involves different processes in the brain: first, perceiving an experience as emotional or intense, and second, encoding that experience into long-term memory,” said Goldfarb, who is also a member of Yale’s Wu Tsai Institute, an interdisciplinary research initiative that explores cognition.
The researchers wanted to examine these processes separately to determine how cortisol affects the brain’s ability to recognize emotional significance and preserve an experience as a lasting memory.
Watching the Brain Form Emotional Memories
To investigate, the Yale team conducted an experiment in which participants took a pill containing either hydrocortisone, a form of cortisol, or an inactive placebo. They then viewed a series of pictures while undergoing functional MRI (fMRI) scanning.
This imaging technique measures changes in blood flow and oxygen levels associated with brain activity, allowing researchers to identify which areas of the brain are more active during different tasks.
As participants examined the pictures, they reported their emotional reactions to each image. The following day, researchers tested how well they remembered what they had seen.
Each person completed the experiment twice, once after receiving hydrocortisone and once after receiving the placebo. The study used a double blind design, meaning neither the participants nor the experimenter knew which substance had been administered during a particular session.
This approach allowed the scientists to compare how the same person’s brain responded with and without the additional cortisol.
A Five-Second Look at Brain Network Activity
One of the study’s most important advances came from the way researchers analyzed the brain scans.
Scientists often study a measurement called functional connectivity, which describes how closely activity in different parts of the brain fluctuates together. When two regions show synchronized patterns of activity, it can indicate that they are participating in related processes.
Traditionally, examining these relationships requires several minutes of brain imaging data. The Yale team instead analyzed functional connectivity during individual trials lasting only around five seconds.
Using these brief snapshots, the researchers tested whether patterns of brain activity could predict two different outcomes: how emotionally intense participants found a picture and whether they would remember that picture the following day.
The approach worked for both. By identifying patterns associated with emotional intensity and memory formation separately, the scientists were able to examine how cortisol influenced each network and the interactions between them.
This gave the researchers a more detailed picture of the changing brain activity associated with emotional memory formation.
Cortisol Changes How Brain Networks Work Together
The results revealed two major effects.
First, cortisol improved participants’ ability to remember emotionally significant experiences, confirming what earlier research had suggested.
Second, and more importantly, the hormone strengthened emotional memory through distinct changes in the brain networks responsible for processing emotion and forming memories.
In networks associated with emotion, cortisol produced more consistent patterns of activity and increased their engagement. This suggests that the hormone helped the brain respond more strongly and reliably to the emotional significance of an experience.
In memory networks, cortisol had a different effect. It made their activity patterns more specialized for emotional information, suggesting that the brain was adjusting how it encoded emotionally meaningful experiences.
The hormone also increased coordination between the networks involved in emotion and memory. In other words, cortisol appeared to help these different brain systems work together more effectively when processing experiences that carried emotional weight.
Together, these findings suggest that stress strengthens emotional memories through several interacting brain mechanisms rather than through a single region or process.
Why Emotional Experiences Can Be So Memorable
The results help explain why stress does not necessarily improve memory for everything. Instead, its benefits appear to be selective, making experiences that feel particularly intense or meaningful more likely to be remembered.
The researchers believe this reflects the brain’s ability to adapt to stressful situations by prioritizing information that may be important.
“Stress responses are fundamentally adaptive and can help you form strong memories — but this is specific to experiences that you find to be emotionally intense or meaningful,” Goldfarb said. “This is in part related to your brain increasing engagement of networks that track emotional intensity. So, if you are stressed out and trying to learn something new, it might help to think about exciting elements or strong feelings connected to what you are learning.”
The findings also point to a potentially useful insight about learning. Connecting information to something exciting, personally important, or emotionally engaging could make it easier to remember, particularly during stressful situations.
Rather than simply disrupting memory, stress can sometimes help the brain identify which experiences deserve special attention and strengthen the networks involved in preserving them.
Other Yale researchers involved in the study include Rajita Sinha, the Foundations Fund Endowed Professor in Psychiatry and professor in the Child Study Center and of neuroscience at Yale School of Medicine (YSM), and Todd Constable, the Elizabeth Mears and House Jameson Professor of Radiology and Biomedical Imaging and professor of neurosurgery at YSM.
The research was supported by grants from the National Institutes of Health.
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