Researchers at Yale University have discovered an important clue. Their study found that cortisol enhances emotional memory by changing how brain networks involved in emotion and memory function and communicate with one another. The findings offer new insight into why some experiences leave powerful, lasting impressions while others quickly fade.

“We all experience stress, and my lab is interested in understanding how stress helps us,” said corresponding author Elizabeth Goldfarb, assistant professor of psychology in the Yale School of Medicine’s Department of Psychiatry and Humanities.

The research was published in the journal Science Advances.

How stress hormones affect emotional memory

Previous studies in humans and rodents have shown that stress and cortisol can improve memory for emotional events. Scientists also know that several brain regions, including the amygdala, play important roles in this process. The amygdala is especially involved in processing emotions and identifying potentially significant experiences.

However, it has been difficult to determine exactly how cortisol enhances memory. Because many brain regions contribute to multiple mental functions, researchers have struggled to establish whether hormones influence emotional responses, memory formation, or both.

“Forming a memory of an emotional experience involves a variety of processes in the brain: first recognizing the experience as emotional or intense, and then encoding that experience into long-term memory,” said Goldfarb, who is also a member of Yale University’s Wu Tsai Institute, an interdisciplinary research initiative focused on cognition.

The researchers set out to examine these processes separately. Their goal was to determine how cortisol affects the brain’s ability to recognize emotional significance and store experiences as lasting memories.

How researchers studied the brain’s emotional memory system

To investigate, the Yale team conducted an experiment in which participants took pills containing either hydrocortisone, a form of cortisol, or an inert placebo. They then viewed a series of photographs while undergoing functional magnetic resonance imaging, or fMRI.

fMRI measures changes in blood flow and oxygen levels associated with brain activity. This allows researchers to identify which brain areas become more active during specific tasks.

As participants viewed the photographs, they reported their emotional reactions to each image. The following day, researchers tested how well they remembered what they had seen.

Each participant completed the experiment twice: once after receiving hydrocortisone and once after receiving the placebo. The study used a double-blind design, meaning that neither the participants nor the experimenter knew which substance had been administered during a particular session.

This design allowed the scientists to compare how the same person’s brain responded with and without added cortisol.

Brain activity can reveal emotional responses in about five seconds

One of the study’s key advances involved the way the researchers analyzed the brain scans.

Scientists often examine a measure called functional connectivity, which describes how closely activity in different brain regions fluctuates together. When two regions show synchronized activity patterns, they may be involved in related processes.

Traditionally, studying these relationships has required several minutes of brain-imaging data. Instead, the Yale team analyzed functional connectivity during individual trials lasting about five seconds.

The researchers used these brief snapshots to determine whether patterns of brain activity could predict two separate outcomes: how emotionally arousing participants found each photograph and whether they remembered it the next day.

The approach successfully predicted both outcomes. By identifying patterns associated with emotional intensity and memory formation separately, the researchers could examine how cortisol affected each network and the communication between them.

This provided a more detailed view of the brain activity involved in forming emotional memories.

Cortisol changes how emotion and memory networks communicate

The results revealed two major effects.

First, cortisol improved participants’ ability to remember emotionally significant experiences, confirming findings from earlier research.

Second, and more importantly, cortisol strengthened emotional memory through distinct changes in the brain networks responsible for emotional processing and memory formation.

In emotion-related networks, cortisol produced more consistent activity patterns and increased emotional engagement. This suggests that the hormone helped the brain respond more strongly and reliably to the emotional significance of an experience.

Cortisol had different effects on memory networks. Their activity patterns appeared to be specialized for emotional information, helping regulate how the brain encoded experiences with emotional meaning.

The hormone also improved coordination between networks involved in emotion and memory. In other words, cortisol appears to help these brain systems work together more effectively when processing emotionally important experiences.

Taken together, the findings suggest that stress strengthens emotional memory through several interacting brain mechanisms rather than through a single brain region or process.

Why stressful and emotional experiences can be easier to remember

The findings help explain why stress does not improve everyone’s memory for everything. Instead, the benefit appears to be selective: experiences perceived as especially intense or meaningful are more likely to be remembered.

Researchers believe this reflects the brain’s ability to adapt to stressful situations by prioritizing information it considers important.

“The stress response is fundamentally adaptive and helps form strong memories, which are specific to emotionally intense or meaningful experiences,” Goldfarb said. “This is partly related to increased engagement in brain networks that track emotional intensity. So if you’re feeling stressed and trying to learn something new, it may be helpful to think about the exciting elements and strong emotions associated with what you’re learning.”

The findings may also offer useful insights into learning. When information is associated with something exciting, personally important, or emotionally appealing, it may be more likely to be remembered, particularly in stressful situations.

Rather than simply disrupting memory, stress may help the brain identify which experiences deserve special attention and strengthen the networks that store them.

Other Yale researchers involved in the study include Endowed Professor of Psychiatry Rajita Sinha of the Yale School of Medicine’s Child Research Center and professor of neuroscience; Professor Todd Constable; Professor Elizabeth Mears, House Jameson Professor of Radiology and Biomedical Imaging; and Yale School of Medicine Professor of Neurosurgery.

The research was supported by a grant from the National Institutes of Health.