Stress is often blamed for making people forget things, but Yale University researchers have discovered that its effects on memory are more complicated.
In an experiment involving 27 participants, scientists found that the stress hormone cortisol improved recognition of emotionally significant information approximately 24 hours later. The findings offer insight into how the brain prioritizes certain experiences during memory formation. They also challenge the assumption that stress affects every memory equally.
Published in Science Advances in December 2025 and highlighted again in October 2026, the study examined how cortisol changes communication between brain networks involved in emotional processing and memory.
The central discovery is that cortisol can strengthen emotional memory by influencing how these brain networks function together.
Yale Researchers Identify How Cortisol Influences Memory
The study found that cortisol improved memory for emotionally significant information under controlled conditions, not overall memory.
Elizabeth Goldfarb, an assistant professor of psychiatry and psychology at Yale at the time, investigated how stress hormones influence memory formation. “We all experience stress, and my lab is interested in understanding how stress can be helpful,” Goldfarb said in a Yale University announcement.
Scientists had previously established that cortisol, a hormone involved in the body’s stress response, could strengthen emotional memories. However, the precise brain mechanisms supporting this effect remained unclear.
The Yale team focused on how cortisol influences the networks that process emotional intensity and form memories.
Their findings suggest that the hormone changes how these systems operate and communicate, offering a more detailed explanation of emotional memory formation.
Inside the Experiment That Revealed the Effect
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Researchers compared participants’ memory performance and brain activity after administering hydrocortisone or an inactive placebo.
The experiment involved 27 people who completed two scanning sessions. Researchers excluded one participant from the final analysis because of a technical problem, leaving 26 participants. During each session, participants received either 20 milligrams of hydrocortisone, a form of cortisol, or a placebo before viewing pictures inside a functional magnetic resonance imaging scanner.
The experiment used a double-blind design, meaning neither participants nor experimenters knew which treatment was administered during a particular session. Participants rated their emotional reactions while viewing combinations of objects and scenes. About 24 hours later, they completed a recognition test to measure how well they remembered the material they had viewed.
Researchers analyzed 52 scanning sessions containing 4,160 experimental trials. These were repeated observations from the same participants, not thousands of separate individuals. The results showed that hydrocortisone improved recognition of emotionally arousing material.
The brain scans provided additional evidence about the activity patterns associated with this effect, allowing researchers to investigate what changed when the hormone was administered.
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How Stress Changes Communication Between Brain Networks
The researchers discovered that cortisol affected emotional processing and memory formation networks differently while increasing coordination between them.
Using a technique called dynamic connectome-based predictive modeling, the team examined brain connectivity during individual experimental trials lasting about five seconds.
This approach let them identify activity patterns linked to participants’ emotional ratings and separate patterns that predicted whether information would be remembered the following day. Under hydrocortisone, networks involved in processing emotional intensity became more consistently engaged.
Meanwhile, memory-related networks developed more specialized activity patterns associated with emotional information.
The researchers also observed greater coordination between these systems. These findings suggest that cortisol influences memory through interactions between multiple brain networks, rather than simply increasing activity in one region.
The discovery offers a clearer understanding of why emotionally significant information can be favored during memory formation.
What the Discovery Means for Understanding Emotional Experiences
The findings show how emotional intensity can influence memory, but they do not establish that everyday stress improves learning.
The research highlights an important distinction between remembering emotionally significant information and remembering every detail of an experience. Cortisol’s effects were selective, meaning the experiment did not demonstrate a general improvement in memory performance.
The findings could help inform future investigations into emotional engagement and learning, although the researchers did not test classroom techniques or workplace training. Consequently, the experiment provides no basis for recommending deliberate stress as a strategy for improving memory.
Instead, it identifies biological processes that may help scientists better understand how emotionally important experiences are encoded.
What Scientists Still Don’t Know About Lasting Memories
The experiment measured recognition about 24 hours later, leaving questions about long-term memory unanswered.
Researchers did not establish whether the observed memory advantage would persist for months or years. The study also involved controlled hormone administration rather than naturally occurring chronic stress or traumatic experiences.
Its relatively small sample limits how confidently the findings can be generalized to wider populations.
Another unresolved issue concerns accuracy. Recognizing previously viewed information does not demonstrate that someone can accurately recall every detail of a complicated emotional experience. Therefore, the findings should not be interpreted as proof that stressful experiences always produce stronger or more reliable memories.
Yale researchers established something more specific: cortisol can alter communication between brain networks in ways associated with better recognition of emotional information.
The discovery adds another piece to our understanding of human memory: an experience’s significance can matter as much as the experience itself.
What makes certain emotional experiences remain vivid in your memory while ordinary moments gradually fade?
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