Research has shown that one of the key elements of our acute stress response (a hormone called cortisol) can impair the part of the brain (the hippocampus) that is involved in encoding memories. Now, a new study shows that stress’ effect on memory is not quite that simple. We actually create stronger memories when we are under stress, with cortisol helping to enhance the brain structure making them, researchers have discovered.
Elizabeth Goldfarb, PhD, assistant professor of psychiatry, is interested in why people remember their experiences the way they do and how stress changes the way we remember. In her latest study, her team found that while cortisol can impair memory signals in the hippocampus as a whole, it also increases connectivity inside this portion of the brain. It explains why we remember emotional experiences better even when our acute stress response is activated. The team published its findings in the Journal of Neuroscience on October 9.
This idea of harnessing the benefits of stress is something that’s very exciting for me.
Elizabeth Goldfarb, PhD
“This is the first time we’ve shown how cortisol can help the hippocampus function better in order to support emotional memory in humans,” says Goldfarb, who was the principal investigator of the study.
How is the brain encoding memory?
This new publication is based on a double-blind, placebo-controlled high-resolution functional magnetic resonance imaging (fMRI) (a type of MRI scan that allows researchers to observe brain function) study involving 27 participants. Individuals were given visually identical pills that either were placebos or contained cortisol. After waiting an hour for their pills to be metabolized, participants viewed a series of images of objects and scenes in an fMRI scanner. The researchers asked them to picture the object and the scene together, and how imagining them interacting made them feel.
The objects shown to the participants were based on prior research that found images of household objects tended to elicit neutral responses, while images of alcoholic beverages often created an emotional response. “If you’re looking at a picture of piña colada and a picture of a beach and imaging them interacting, in general, people are more likely to report feeling happy,” Goldfarb explains.
The next day, participants returned to the lab, where the team tested their memory for the object-scene pairs. About a week later, they repeated the experiment after taking the other pill—if they received a pill with cortisol the first time, for instance, they took the placebo the next week.
What is cortisol’s role in amplifying emotional memory?
The study supported that memory becomes stronger under cortisol. In the placebo group, when participants viewed an object that elicited an emotional response, they were less likely to remember its scene pair. This is because under normal conditions, we tend to focus our attention on objects that draw an emotional response from us. But with cortisol, the greater the emotional response elicited, the more successful participants were at remembering the scene.
They also showed how the brain can help make these memories better. The hippocampus is not a monolith—it is made up of different subparts that vary in their connectivity and cortisol receptors. Using a new high-resolution fMRI approach, the researchers were able to take a closer look at these different regions. “We didn’t want to see the response of the hippocampus as a whole, but rather how it talks to itself,” says Goldfarb.
Their findings revealed that cortisol actually increased connectivity within the hippocampus. “We discovered this pathway where cortisol is helping the hippocampus talk to itself, and that helps people remember emotional experiences better,” says Goldfarb.
This study calls into question the dominant narrative about stress being bad for hippocampal function. Instead, it supports that stress is an adaptive signal with evolutionary benefit for humans. “This idea of harnessing the benefits of stress is something that’s very exciting for me,” says Goldfarb.